BY: K. Sai Manogna (MSIWM014)

The potential for spreading through drinking water is the emerging pathogenic bacteria of concern outlined here, but they do not correlate with the existence of E. Coli or with other measures of the consistency of drinking water widely used such as coliform bacteria. There are no satisfactory microbiological markers of their existence in most cases. To understand the real nature and dimension of the diseases caused by water polluted with these bacteria and the ecology of these pathogens, further studies are required.

Mycobacterium Avium Complex (Mac):

The complex Mycobacterium avium (Mac) consists of 28 serovars of two species: Mycobacterium avium and Mycobacterium intracellular. With the discovery of disseminated infection in immunocompromised individuals, especially people with HIV and AIDS, the Mac species’ significance was recognized. MAC members are deemed to be opportunistic human pathogens. A wide range of environmental sources, including coastal waters, rivers, lakes, streams, wetlands, springs, soil, piped water supplies, plants, and house dust, have defined Mac species. Mac species have been isolated from the delivery systems of natural water and drinking water in the USA. The ubiquitous existence of Mac organisms stems from their ability under varied conditions to thrive and evolve. Mac species can proliferate at temperatures up to 51°C in water and expand over a broad pH range in natural waters. These mycobacteria are incredibly resistant to the use of chlorine and other chemical disinfectants in drinking water care. Standard drinking-water treatments may not remove Mac species but may substantially reduce the numbers present in the source water to a level that poses a negligible risk to the general public if it is running satisfactorily. In delivery systems, the entryway for these mycobacteria is through leaks. For their continued presence in distribution systems, the growth of Mac organisms in biofilms is probably significant.

Slow-growing mycobacteria can be present in the surface biofilm at densities higher than 4,000 per cm2, producing a potentially high exposure level. The signs of Mac infections result from either respiratory or gastrointestinal colonization, potentially spreading to other places in the body. Exposure to Mac species may occur through the consumption of contaminated foodstuffs, the inhalation of air containing contaminated soil particles, or through touch or ingestion, aspiration or aerosolization of the organisms containing drinking water.  Unlike gastrointestinal pathogens, where E. No appropriate indicators have been identified to signal increasing Mac species concentrations in water systems, and coli can suggest possible presence.

Helicobacter pylori:

As a significant etiologic agent for gastritis, Helicobacter pylori has been cited and has been involved in the pathogenesis of duodenal ulcer and peptic disease and gastric carcinoma. Most people who are infected by this pathogen, however, remain asymptomatic. Using methods based on history, H. There has been no isolation of pylori from environmental sources, including water. Molecular methods have, on the other hand, been useful in detecting the pathogen.

Fluorescence in situ hybridization (FISH) has been successfully used to detect this pathogen in drinking water delivery systems and other water bodies. To detect the presence of H, a polymerase chain reaction was also used. Pylori DNA in drinking water, especially biofilm-associated. In biofilms for drinking-water, H. Pylori cells lose culturability rapidly and enter a viable but non-culturable state. Cells persist for more than one month in these biofilms, with densities exceeding 106 cells per square cm. It remains unclear how the organism is transmitted. Nevertheless, the fact that it has been oral-oral or fecal-oral transmission is demonstrated by recuperation from saliva, dental plaques, stomach, and fecal samples. Water and food tend to be of less immediate significance, but they can still play a significant role in improper sanitation and hygiene.

Aeromonas Hydrophyla:

Over the past years, A. Hydrophila has received attention as an opportunistic pathogen for public health. The elderly, children under the age of five, and immunosuppressed persons may play a significant role in intestinal disorders. Gram-negative, non-spore-forming, rod-shaped, facultative anaerobic bacilli belonging to the Aeromonadaceae family are Aeromonas hydrophila. Even though the dominant species is typically hydrophila, whereas other aeromonads, such as A.Sobria, and A.Caviae were isolated from human feces and water sources. Species of Aeromonas, including A. Hydrophila, in the field, are ubiquitous. It is also segregated from food, potable water, and aquatic ecosystems. Concentrations of Aeromonas spp. in safe rivers and lakes Typically, 102 colony-forming units (CFU)/mL are around. In general, groundwater contains less than 1 CFU/mL. It was noticed that drinking water immediately leaving the treatment plant contained between 0 and 102 CFU/mL. Drinking water can show higher concentrations of Aeromonas in delivery systems due to the growth of biofilms. With Aeromonas spp. growth was observed between 5° – 45° C.

A. Hydrophila is immune to standard treatments with chlorine and is likely to live within biofilms. Ingestion of infected water or food or touch of the organism with a break in the skin are the typical routes of infection suggested for Aeromonas. A potential source of pollution for human beings may be drinking or natural mineral water. There was no recorded person-to-person transmission.

Nitrogen Fixation

BY- K. Sai Manogna (MSIWM014)

Any natural or industrial process that allows free nitrogen (N2), a relatively inert gas abundant in the air, chemically combines with other components to form more reactive nitrogen compounds, such as ammonia, nitrates, or nitrites. 

Nitrogen does not react with other elements under ordinary conditions. However, in all fertile soils, in all living organisms, in many foodstuffs, in coal, and such naturally occurring chemicals as sodium nitrate and ammonia, nitrogenous compounds are contained. As DNA, nitrogen is also present in each living cell’s nucleus. 

 Role of nitrogen in nature: 

The growth of all organisms is dependent on the availability of mineral nutrients, and none is more crucial than nitrogen, which, as an integral component of proteins, nucleic acids, and other cellular constituents, is required in large quantities. In the earth’s atmosphere, there is an ample supply of nitrogen – approximately 79 percent in the form of N2 gas. However, since there is a triple bond between the two nitrogen atoms, N2 is unavailable for most species, rendering the molecule virtually inert. It must be ‘fixed’ (combined) in the form of ammonium (NH4) or nitrate (NO3) ions for nitrogen to be used for growth. The weathering of rocks releases these ions so slowly that fixed nitrogen availability has a marginal effect. Therefore, nitrogen is always the limiting factor for the growth and development of biomass in all habitats where there are an adequate climate and water availability to sustain life. 

In nearly all aspects of the availability of nitrogen and thus for life support on earth, microorganisms play a central role: 

Some bacteria can turn N2 into ammonia; they are either free-living or in symbiotic relationships with plants or other species (e.g., termites, protozoa). Other bacteria cause ammonia transformations to nitrate, and many bacteria and fungi degrade organic matter from nitrate to N2 or other nitrogen gases, releasing fixed nitrogen for reuse. These processes also lead to the cycle of nitrogen. 

Examples of nitrogen fixing bacteria

Biological Nitrogen Fixation Process 

Nitrogen cycle: The cycle of nitrogen is a repeating cycle process in which nitrogen travels through the soil, atmosphere, water, plants, animals, and bacteria, both living and non-living things. Nitrogen must change types in order to pass through the various parts of the cycle. Nitrogen occurs as a gas (N2) in the atmosphere, but it exists as nitrogen oxide, NO and nitrogen dioxide, NO2, in the soils and can be present in other forms when used as a fertilizer, such as ammonia, NH3, which can be further converted into another fertilizer, ammonium nitrate or NH4NO3. 

nitrogen cycle

The nitrogen cycle occurs in five steps: 

  1. Nitrogen fixation, 
  2. Mineralization, 
  3. Nitrification, 
  4. Immobilization, and 
  5. Denitrification. 

Microbes in the soil convert nitrogen gas (N2) into volatile ammonia (NH3) in this picture, so the volatilization is called the fixation process. Leaching is when specific nitrogen sources (such as nitrate or NO3) are dissolved in water, escaping from the soil and potentially polluting waterways. 


In this process, nitrogen moves into the soil from the atmosphere. A massive reservoir of nitrogen gas is in the earth’s atmosphere (N2). However, this nitrogen is not ‘available to plants because without transforming, the gaseous form cannot be used directly by plants. N2 must be converted by a mechanism called nitrogen fixation in order to be used by plants. 

1. In the atmosphere, fixation transforms nitrogen into which plants can absorb through their root systems.

2. When lightning gives the energy required for N2 to react with oxygen, creating nitrogen oxide, NO and nitrogen dioxide, NO2, a small amount of nitrogen can be fixed via rain or snow; these sources of nitrogen then enter the soil. 

3. By the industrial process that produces fertilizer, nitrogen may also be fixed. 

4. This method of fixation takes place under high pressure and heat, during which nitrogen(atmospheric) and hydrogen, combined to form ammonia (NH3); which can then be further processed for the development of ammonium nitrate (NH4NO3), a form of nitrogen which can be applied to the soil and used by plants. 

5. The majority of nitrogen fixation occurs naturally by bacteria in the soil. 

6. Some bacteria bind to plant roots and have a relationship with the symbiotic plant.

7. Through photosynthesis, the bacteria get energy, and in exchange, they fix nitrogen in a form that requires the plant. The fixed nitrogen is then transferred to other parts of the plant and used to shape the plant’s tissues to expand. 

8. Other bacteria live freely in soil or water, without this symbiotic relationship, and can fix nitrogen. These bacteria can also produce sources of nitrogen that species can use. 


This process occurs in the soil from organic sources, such as manure or plant materials, nitrogen transfers to an inorganic source of nitrogen used by plants. The plant’s nutrients are gradually used up, and the plant dies and decomposes. In this stage of the nitrogen cycle, this becomes true. 

1. Mineralization occurs when bacteria, such as animal manure or decomposing plant or animal waste, operate on organic material, and begin to transform it into a nitrogen source that plants can use. 

2. All plants under cultivation, except legumes, obtain the nitrogen they need from the soil. 

3. Legumes get nitrogen through fixation that happens in their root nodules. 

4. NH3 is ammonia, the first source of nitrogen formed by the mineralization process. The NH3 in the soil then reacts to form ammonium, NH4, with water. 

5. This ammonium is kept in the soils and is accessible via the symbiotic nitrogen-fixing relationship mentioned above for use by plants that do not get nitrogen. 


1. The third step, nitrification, also takes place in the soil. The ammonia formed during mineralization in the soils is converted into nitrites, NO2- and NO3-nitrates during nitrification. 

2. The plants and animals consuming the plants will use nitrates. 

3. In the soil, some bacteria can convert ammonia into nitrites. 

4. While nitrite is not usable by plants and animals directly, other bacteria may convert nitrites into nitrates, a form that is usable by plants and animals. 

5. For the bacteria involved in this process, this reaction provides energy. 

Nitrosomonas and Nitrobacter are the bacteria that help in fixing nitrogen. Nitrobacter transforms nitrites into nitrates; Nitrosomonas converts nitrites to ammonia. Only in the presence of oxygen can both forms of bacteria function. For plants, the nitrification process is essential as it creates an additional stash of usable nitrogen that can be consumed by the plants via their root systems. 


Immobilization, often defined as the reverse of mineralization, is the fourth stage of the nitrogen cycle. Together these two processes regulate the amount of nitrogen in the soil. Microorganisms living in the soil, just like plants, require nitrogen as an energy source. 

1. When the residues of decomposing plants do not contain enough nitrogen, these soil microorganisms pull nitrogen from the soil. 

2. These nitrogen sources are no longer available to plants when microorganisms take in ammonium (NH4+) and nitrate (NO3−) and can cause nitrogen deficiency or a lack of nitrogen. 

3. Therefore, immobilization binds up nitrogen in microorganisms. 

4. Immobilization, however, is essential because it helps to regulate and balance the amount of nitrogen in microorganisms in the soils by binding it up or immobilizing the nitrogen. 


1. Nitrogen returns to the air in the fifth stage of the nitrogen cycle when bacteria transform nitrates to atmospheric nitrogen (N2) via denitrification. 

2. As the gaseous form of nitrogen travels into the atmosphere, it results in an overall loss of nitrogen from soils.

Not enough nitrogen in the soils makes plants hungry, while too much of a good thing can be harmful: plants and even livestock can be contaminated by excess nitrogen! The contamination of our water supplies by excess nitrogen and other nutrients is a significant concern, as the decomposition of dead algae blooms is suffocating marine life. Farmers and communities need to increase crop absorption of added nutrients and adequately manage the excess of animal manure.


BY: Reddy Sailaja M (MSIWM031)


  • Microorganisms have the ability to adapt themselves to the changing conditions prevailing in the environment. Factors that influence microorganism’s survival could be physical, chemical or environmental.
  • Some microorganisms go in search of favorable conditions for survival, while some will become dormant till the favorable conditions arrive.
  •  One such mechanism adapted by certain gram-positive bacteria is the development of ‘endospores.  Gram positive bacteria, especially genera, Bacillus and Clostridium have the ability to form endospores in response to harsh conditions, nutrient deprivation in particular.
  •  When there is starvation due to nutrient deprivation, these bacteria produce most resistant and dormant ‘endospore ‘structures that preserve cell’s genetic composition to with stand the harsh assaults like high temperature, desiccation, UV radiation, chemical and enzymatic damage.
  •  Moreover, endospores are the most resistant form of “spores” or “cysts” produced by many bacteria and are resistant to most of the antibiotics. Altogether, endospores are resistant and dormant structures of life survival forms of bacteria and fight against harsh environments.



Formation of endospore

Figure 1: Development of Endospore

  • Bacillus subtilis is the model organism used to study and understand the development of endospore during the process is called sporulation.
  •  It takes many hours to complete endospore formation. Morphological changes that occur during this process are used as markers to classify stages of endospore development. Stage I is that when the bacterial cell is under favorable conditions.
  • Under unfavorable conditions, bacterial cell initiates endospores formation by asymmetric cell division and is called Stage II. Asymmetric cell division results in the formation of a larger mother cell and a smaller forespore (or pre-spore) with septum in between them.
  • Even though, these two cell types in stage II has varied developmental fates, intercellular communication system harmonize cell specific gene regulation by influencing specialized sigma factors in the cells.
  •  In stage III, peptidoglycan present in the septum gets dissolved and the mother cell engulfs forespore, which becomes a cell within a cell.
  • In the stages IV+V, cortex and the spore coat layers are formed around the forespore, leading to the production of endospore specific compounds.
  •  In the stages VI+VII, further dehydration and the maturation of the endospore happens. Finally, the mother cell dies by apoptosis (also called programmed cell death) and the endospore is release into the environment and remains dormant until favorable conditions prevail.

Endospore structure

Endospore structure comprises of multiple layers of coats that resist against harsh surrounds. The following table details various layers (from outer to inner), their compositions and functions.

Endospore layerCompositionFunction
ExosporiumCarbohydrates, proteins  and lipidsGives hydrophobic character to the endospore and is responsible for endospore pathogenicity
Spore coatCoat proteins cross-linked with disulfide bondsActs as primary permeability barrier and allows only smaller molecules like germinants
Outer membraneNot known
CortexPeptidoglycan without teichoic acids with low cross linkingStructural differences in the peptidoglycan of cortex and germ cell wall allow selective degradation of outer protection, germination of endospore and transformation of germ cell wall into vegetative cell.
Germ cell wallPeptidoglycan
Inner membraneSimilar to cell membrane composition. Germinant receptorsVaried fluidity and permeability and decreased mobility of the membrane lipids make the structure highly impermeable to the molecules including water, protecting core. Germinant receptors allow binding of germinants and begin germination and vegetative growth.
CoreBacterial DNA, RNA, ribosomes, essential enzymes, small acid-soluble spore proteins (SASPs), Dipicolinic acidDehydrated state protects enzymes and heat resistance. SASPs protect DNA from destructive chemicals and enzymes by forming shield. SASPs also function as carbon and energy source during germination into vegetative cell. Dipicolinic acid also protects endospore’s DNA against harsh environment.

Figure 2: Structure of endospore

Mechanism of sporulation

  • Sporulation of endospores is under the control of five kinases, namely KinA, KinB, KinC, KinD and KinE that act under phosphorelay signal transduction mechanism.
  • Each of these kinases gets activated based on specific environmental stimuli. Under a specific kind of environmental stimulus, one of the five sensor kinases undergoes autophosphorylation at conserved histidine residue by an ATP dependent reaction through a protein called Spo0F. Then the Spo0F transfers the phosphate to Spo0B, that act as a mediator and delivers signal to Spo0A.
  •  Spo0A further positively regulate genes necessary for sporulation and negatively regulate genes required for vegetative growth.

Figure 3: Mechanism of sporulation

Functions of endospores

  • Endospores mainly resist harsh conditions like high temperatures, disinfectants, radiation, etc.
  •  Endospores are reported to survive for millions of years. For example, viable endospores were isolated from gastrointestinal tract of a bee that was embedded in amber around 25-40 years ago.
  • Dipicolinic acid and SASPs are crucial in protecting core of the endospore that contains genetic material.

Infectious diseases caused by endospores

In spite of defensive mechanism, endospores also transmit some infectious diseases as follows:

i)Anthrax – caused by Bacillus anthracis endospores when inhaled, ingested will germinate under suitable conditions and spread the infection

ii)Botulism – Caused by Clostridium botulinum. Spreads through unprocessed food and infect

iii) Tetanus – caused by Clostridium tetani. Spread through anaerobic wounds and cause infection.

 Other infectious diseases like gas gangrene and pseudomembranous colitis are also popular.



Introduction :

Any disease caused by bacteria involves bacterial diseases. Bacteria, which are small types of life that can only be seen through a microscope, are microorganisms. Viruses, some fungi, and some parasites include other types of microorganisms. Millions of bacteria usually reside in the skin, intestines, and genitals. The vast majority of bacteria cause no disease, and many bacteria are beneficial and even required for good health. Often, these bacteria are referred to as good bacteria or healthy bacteria. 

Pathogenic bacteria are considered dangerous bacteria that cause bacterial infections and illnesses. When these invade the body and begin to replicate and crowd out healthy bacteria or develop in typically sterile tissues, bacterial diseases occur. Toxins that damage harmful bacteria can also release the body.

Typhoid :

An infectious, potentially life-threatening bacterial infection is typhoid fever, also called enteric fever. Typhoid fever is caused by the Salmonella enteric serotype Typhi bacterium (also known as Salmonella Typhi), carried into the blood and digestive tract by infected humans and spreads by food drinking water contaminated with infected feces to others. Typhoid fever signs include fever, rash, and pain in the abdomen. 

Fortunately, typhoid fever, particularly in its early stages, is treatable, and if one chooses to live in or fly to high-risk areas of the world, a vaccine is available to help prevent the disease.

Incubation Period :

Typhoid and paratyphoid infections have an incubation period of 6-30 days. With steadily rising exhaustion and a fever that rises daily from low-grade to as high as 102 ° F to 104 ° F ( 38 ° C to 40 ° C) by the third to the fourth day of illness, the onset of illness is insidious. In the morning, fever is usually the lowest, peaking in the late afternoon or evening. 

Pathophysiology :

1. When present in the gut, all pathogenic Salmonella species are swallowed up by phagocytic cells, moving them through the mucosa and presenting them to the lamina propria macrophages. 

2. Across the distal ileum and colon, nontyphoidal salmonellae are phagocytized. Macrophages identify pathogen-associated molecular patterns (PAMPs) such as flagella and lipopolysaccharides with the toll-like receptor (TLR)-5 and TLR-4 / MD2 / CD-14 complex. 

3. Macrophages and intestinal epithelial cells are then attracts the interleukin 8 (IL-8) T cells and neutrophils, inducing inflammation and suppressing the infection. 

4. Unlike the nontyphoidal salmonellae, S typhi and paratyphi penetrate mainly via the distal ileum into the host system. They have specialized fimbriae that bind to the epithelium over lymphoid tissue clusters in the ileum, the critical point of relay for macrophages moving into the lymphatic system from the stomach. 

5. The bacteria then attract more macrophages by activating their host macrophages.

6. Typhoidal salmonella co-opts the cellular machinery of the macrophages for their reproduction, as they are transported to the thoracic duct and lymphatics to the mesenteric lymph nodes and then to the reticuloendothelial tissues of the spleen, bone marrow, liver, and lymph nodes. 

7. Once there, until some critical density is reached, they pause and begin to multiply. Afterward, to reach the rest of the body, the bacteria cause macrophage apoptosis, breaking out into the bloodstream. 

8. By either bacteria or direct extension of infected bile, the bacteria then invade the gallbladder. The effect is that in the bile, the organism re-enters the gastrointestinal tract and reinfects patches of Peyer. 

9. Usually, bacteria that do not reinfect the host are shed in the stool and are then available for other hosts to invade.

Epidemiology :

The International 

Worldwide, typhoid fever occurs mostly in developing countries where sanitary conditions are low. In Asia, Latin America, Africa, the Caribbean, and Oceania, typhoid fever is endemic, but 80 percent of cases originate from Bangladesh, China, India, Indonesia, Laos, Nepal, Pakistan, or Vietnam. In underdeveloped countries, typhoid fever is the most common. About 21.6 million people are infected by typhoid fever (incidence of 3.6 per 1,000 population), and an estimated 200,000 people are killed every year. 

Most cases of typhoid fever occur among foreign travelers in the United States. The average annual incidence of typhoid fever by county or area of departure per million travelers from 1999-2006 was as follows:

Outside Canada / United States, Western Hemisphere-1.3 

Africa-7.6 Africa 


India-89 (in 2006 122) 

Complete (except for Canada / United States, for all countries)-2.2 

Morbidity / Mortality :

Typically, typhoid fever is a short-term febrile condition with timely and effective antibiotic care, requiring a median of 6 days of hospitalization. It has long-term sequelae and a 0.2 percent mortality risk when treated. Untreated typhoid fever is a life-threatening disease that lasts many weeks, frequently affecting the central nervous system, with long-term morbidity. In the pre-antibiotic age, the case fatality rate in the United States was 9 -13%.

Sex : 

Fifty-four percent of cases of typhoid fever recorded between 1999 and 2006 in the United States included males. Moreover, race has no predilection. 

Age : 

Many confirmed cases of typhoid fever include children of school age and young adults. The true incidence is, however, thought to be higher among very young children and babies. The presentations may be atypical, that ranges from a mild febrile disease to severe convulsions, and the infection of S.typhi may go unrecognized. In the literature, this could account for contradictory reports that this category has very high or very low morbidity and mortality rate.

Symptoms :

Typhoid fever symptoms typically occur five to 21 days after food or water infected with Salmonella Typhi bacteria is consumed and can last up to a month or longer. Typical Typhoid Fever signs include: 

i. Pressure in the abdomen and tenderness 

ii. Perplexity 

iii. Fatigue and Weakness 

iv. Trouble focusing 

v. Constipation or diarrhea

vi. Headaches 

vii. The Nosebleeds 

viii. A dry cough 

ix. Impoverished appetite 

x. Rash (small, flat, red rashes that are also known as rose spots on the belly and chest) 

xi. Lethargy 

xii. Swollen lymph ganglions 

xiii. Chills and Fever. With typhoid fever, persistent fever of 104 degrees Fahrenheit is not rare. 

Symptoms: life-threatening 

Typhoid fever, including intestinal bleeding, kidney failure, and peritonitis, may lead to life-threatening complications. If they are with anyone who has any of these signs, seek urgent medical attention : 

Bloody stools or severe rectal bleeding 

A shift in consciousness or alertness level 

Confusion, delirium, disorientation, or hallucinations 

Unexplained or chronic dizziness 

Dry, broken lips, tongue, or mouth 

Unresponsiveness or lethargy 

Not urinating tiny quantities of tea-colored urine or urinating it. 

Extreme pain in the abdomen 

Extreme diarrhea in patients 

Extreme signs in infants include sunken fontanel (soft spot) at the top of the head, lethargy, no weeping tears, little or no wet diapers, and diarrhea. Infants two months of age or younger, be especially concerned about fever.

Causes :

The Salmonella Enteric Serotype Typhi (Salmonella Typhi) bacterium is responsible for typhoid fever. Via ingestion of infected food and water, Salmonella Typhi can enter and infect the body. By being washed in polluted water or being touched by an infected person with unwashed hands, food can become contaminated with the bacteria. Drinking water can become infected with untreated Salmonella Typhi-containing sewage.

Risk factors :

A variety of variables improves the chances of contracting typhoid fever. In developing, non-industrialized countries, typhoid fever is a significant health threat, although rare in the United States, Canada, and other industrialized countries. Factors of vulnerability include: 

i. Near contact with individuals infected or recently infected 

ii. Travel to areas with more frequent and widespread outbreaks of typhoid fever, such as India, Southeast Asia, Africa, and South America

iii. Avoiding contact with a person who has or has signs of typhoid fever, such as abdominal pain, headache, and fever

iv. Residence in a developing world or continent with inadequate treatment facilities for water and sewage or poor hygiene practices 

v. Due to diseases such as HIV / AIDS or drugs such as corticosteroids, the compromised immune system 

vi. Do not eat fruits and vegetables that are unable to peel. Eating fully cooked, hot, and still steaming foods. Unless it is made from distilled water, drinking only bottled water and not using ice 

vii. Before visiting high-risk areas, having vaccinated against typhoid fever 

viii. During and after contact with an individual who has typhoid fever or with an individual who has signs of typhoid fever, such as abdominal pain, headache, rash, and fever, washing hands regularly with soap and water for 15 seconds 

ix. Washing hands regularly for at least 15 seconds with soap and water, particularly before handling food and after using the toilet, touching feces, and changing diapers

Diagnosis :

1. Salmonella bacteria infiltrate the small intestine following the ingestion of infected food or drink and temporarily enter the bloodstream. 

2. The bacteria are transported into the liver, spleen, and bone marrow by white blood cells, replicating and re-enter the bloodstream. 

3. At this point, people develop symptoms, including fever. Bacteria invade the biliary system, gallbladder, and the intestinal lymphatic tissue. 

4. Here, in high numbers, they multiply. In the digestive tract, the bacteria move and can be found in stool samples. 

5. Blood or urine samples will be used to diagnose if a test result is not exact.

Treatment :

Typhoid fever is a treatable condition, and a complete course of antibiotics, such as ampicillin, trimethoprim-sulfamethoxazole, or ciprofloxacin, may also be used to cure it. Treatment can include rehydration with intravenous fluids and electrolyte replacement therapy in some severe cases. Usually, with care, symptoms improve within two to four weeks. If they have not been treated completely, symptoms may return. One needs to take the antibiotics for as long as needed to treat typhoid fever and follow up with the doctor for a series of blood and stool tests to ensure that they are no longer infectious. 

Few people infected with Salmonella Typhi become carriers, which indicates that the bacteria are present in the intestines and bloodstream and are shed in the stool even after they no longer have disease symptoms. Because of the carrier effect, it is essential to understand that they might still transmit the disease by contaminating food and water even after receiving treatment for typhoid fever. Before traveling outside developed regions, such as the United States, Canada, northern Europe, Australia, New Zealand, and Japan, it is vital to avoid the disease by getting vaccinated. During epidemic outbreaks, immunizations are also recommended, although the vaccination is not successful.

Prevention :

A larger number of typhoid cases usually occur in countries with less access to clean water and washing facilities. 

Immunization :

Vaccination is advised while traveling to a region where typhoids are prevalent. 

It is recommended to get vaccinated against typhoid fever before traveling to a high-risk area. 

Oral treatment or a one-off injection can be done : 

Oral: an attenuated, live vaccine. It consists of 4 tablets, one of which is taken every other day, the last of which is taken one week before departure. 

Shoot, the inactivated vaccine, was given two weeks before the ride. 

Vaccines are not 100 percent successful, and when eating and drinking, caution should always be exercised. 

Two forms of typhoid vaccine are available, but a more potent vaccine is still required. The vaccine’s live, oral form is the strongest of the two. It also protects individuals from infection 73 percent of the time after three years. This vaccine has more side effects, however. If the person is currently ill or if he or she is under the age of 6 years, vaccination should not begin. The live oral dose should not be taken by someone who has HIV. There may be adverse effects of a vaccine. One in every 100 people is going to feel a fever. There may be stomach complications following the oral vaccine, nausea, and headache. For any vaccine, however, serious side effects are uncommon. 

Typhoid removal :

Even if typhoid symptoms have passed, it is still possible to bear the bacteria, making it impossible to stamp out the disease because when washing food or communicating with others, carriers whose symptoms have terminated may be less vigilant. 

Prevention of Infection :

Via touch and ingestion of contaminated human waste, typhoid is propagated. This can happen through a source of water that is tainted or when food is treated. 

Some general rules to obey while traveling to help reduce the risk of typhoid infection are the following: 

i. Drink water, preferably carbonated, in glasses. 

ii. Do not have ice for drinks. Stop raw fruit and vegetables, cut the fruit, and not eat the cut on your own. Eat only food that is still hot, and avoid eating at street food stands.

iii. If it is impossible to acquire bottled water, ensure the water is heated for at least one minute on a rolling boil before consumption. 

iv. Be wary of eating something that anyone else has dealt with. 

Related Disorders :

There may be similar symptoms of the following conditions to those of typhoid fever. For a differential diagnosis, similarities may be helpful: 

Salmonella Poisoning :

In foodborne diseases, this is the most common cause of disease. These bacteria can contaminate meat, dairy, and vegetable products. In warm weather and children under the age of seven, outbreaks are more prevalent. The most common initial symptoms are nausea, vomiting, and chills. These are accompanied by stomach pain, diarrhea, and fever that can last for several weeks to five days. Intoxication with salmonella is a type of gastroenteritis. The CDC reports about 2 to 4 million salmonellosis cases per year in the United States. 

Cholera :

Cholera is a bacterial infection characterized by extreme diarrhea and vomiting that affects the whole small intestine. A toxin produced by the bacteria Vibrio cholerae is the source of the symptoms. The disease is transmitted by drinking water or consuming fish, vegetables, and other foods contaminated with Cholera’s excrement.

Botulism :

Botulism is also a form of gastroenteritis caused by a bacterial toxin. A neuromuscular poison is this toxin. In three types, it occurs foodborne, wound, and infantile botulism. The foodborne type is the most popular. Besides nausea, vomiting, diarrhea, and stomach pain, the patient can feel exhaustion, fatigue, headache, and dizziness.

Ptomaine Poisoning in the United States’ fourth most prevalent cause of bacterial foodborne disease. It is caused by the enterotoxin protein released after consuming foods that are contaminated, usually meat products. Extreme stomach cramps and diarrhea are characteristics of the disease. Nausea also happens sometimes. Vomiting and fever are rare. 

Isolation And Culturing Of Microbes From Food


  • Microorganisms are abundant and found in food stuff as well.
  • The microbes found on food can be pathogenic in nature and may cause various diseases.
  • The identification of such microbes is necessary to study and research on infectious agent.
  • Primary culture from food stuff is a mix culture of various microbes which has to be isolate form each other and identify for research.
  • The procedure below is used to isolate and cultivate pure culture form food stuffs.


  • Nutrient agar plate
  • Food sample
  • Spreader
  • Micropipette
  • Test tube


  • Take nutrient agar plate and well label them.
  • In one test tube take 4.5 ml autoclaved water and add small quantity of food sample in it
  • Mix thoroughly, after that with the help of micropipette take 100 microliter of the mixture and spread onto the petri plate with a spreader.
  • Finally put the petri plates in the incubator for 18-24 hours at 37o C.
  • After the incubation period mark the different colonies with marker.
  • Now pick each single colony with an inoculating loop and streak on nutrient agar plate.
  • Put the petri plates inside the incubator for 18- 24 hours at 37o C.


  • After 18-24 hours examine the plates for bacterial growth.


  • Record the result of isolated colonies in tabular form.



Food Spoilage:

It refers to change in Physical and Chemical property of food, making food unfit for Consumption. Invasion of microorganisms like bacteria and fungi usually causes spoilage of food.


Food spoilage generally occurs due to Physical, Chemical or Biological agents that changes colour, flavour, appearance, odour and other properties of food. Shelf life of most of the natural foods is very less and is perishable, for example, meat, fish and bread can spoil easily. Decomposition of food generally involves 3 processes: Putrefaction (chemical breakdown of food or decay of organic matter), Fermentation (chemical breakdown of substances by action of microorganisms, yeast), Rancidity ( refers to oxidation of fats).

Natural Contamination:

It refers to contamination of food when microorganisms themselves attaches to food in its growing stages and this kind of contact is essential for certain kinds of food. For example, Yeasts contaminates fruit for carbohydrates fermentation.

Artificial Contamination:

This type of contamination occurs during handling of food when food is under various stages of production like, packaging, storage, etc. Improper handling of food during this stages results in contamination of food by microorganisms.

Intrinsic factors of food like pH, redox potential, H2o activity determines the type of microflora growing on the food. This final composition of microflora is responsible for food spoilage.

Types of Food Spoilage:

1.Microbial Spoilage:

Microorganisms associated with food are:

Bacteria, Filamentous Fungi, Viruses, Yeasts, and animal parasites.


They are associated with both plant and animal foods. Bacteria are associated with food intoxication and spreading of food borne diseases.


Acenatobacter Gram negative- present in raw and prepared foods like beef and poultry carcasses.

Aero monas: gram negative, responsible for spoilage of fish.

Alkaligans: gram negative, responsible for spoilage of egg and dairy products.

Citrobacter: gram negative, it is responsible for spoilage of vegetables and fresh meat.

Corynebacterium: gram positive, involved in spoilage of vegetables and  meat.

Filamentous Fungi:

When food is left for one or more day covered, tangled mass of furry growth appears on food which is called fungi or mould. Fungi are responsible for spoilage of Grains, nuts, and fruits as they have low pH and H20 activity.


Mucor: Zygomycotena-common contaminant of fruits, berries and nuts.

Rhizopus: Zygomycotena- known commonly as bread mould. It is more prevalent in fermented and stored foods.

Claviceps: Ascomycotena-  produces toxic alkaloids in cereals, when consumed can cause Hallucinations.


Contamination by yeasts results in Souring of milk.


Candida: most common contaminant of dairy products, fresh fruits, and alcoholic beverages.

Saccharomyces: spoilage of fruits and fruit products.

Torulopsis: responsible for spoilage of beef, creamed butter, condensed milk, etc.


viruses found in food are termed as enteric or intrinsic viruses.


Enterovirus, Adenovirus, Reovirus, Hepatitis A virus.

Animal Parasites:

They belong to 3 distinct groups:

Protozoa: Giardia, Entamoeba Hystolytica

Flatworms: Taenia, Fasciola

Roundworms: Ascaris

2. Physical Spoilage:

Physical Spoilage refers to damaging of food during Harvesting, Processing or distribution of food. During such processes there are high chances of food spoilage if proper measures are not followed. The damage increases the chance of spoilage as the outer layer is completely broken or bruised. For example- Canned foods gets spoiler easily if the cans are not properly packed with lid or are contaminated during processing.

3. Chemical Spoilage:

Chemical reactions in food are responsible for change of colour, texture and taste of the food products. Generally foods are fresh especially vegetables and animal food, but after harvesting and slaughtering, chemical changes begin automatically in the food and the quality of food becomes deteriorated.

4. Enzymic Spoilage:

Enzymes acts as biological catalyst to carry out biological reactions in cell and play an important role in biochemical reactions. After death of cells or tissues, enzymes play a role in its decomposition by a process called Autolysis( self destruction )

Example: In tomatoes, some enzymes helps it for ripening, but at the same time there are certain enzymes which are responsible for its decay. Once enzymic Spoilage is underway, it damages the outer skin of tomato and exposes it to mould growth and decay.

Factors Affecting Food Spoilage:

  1. Water Content: Amount of water holding capacity in foods is referred to as it’s water activity.(WA). Water activity of most of the fresh fruits is approximately 0.99, which makes them more susceptible to microbial growth.
  2. Environmental Conditions: Environmental influence on food is the major concern. When food is exposed to intrinsic conditions like temperature, air, or even small amount of moisture, can result in growth of Micro-organisms. Changing environmental conditions can help to prevent spoilage. For example- storing food at lower temperature can prevent it from spoiling.
  • Packaging and storage: Packaging of foods is after processing is very vital as it protects food from harmful contaminants and also from various other factors like environment, temperature, etc. The type of packaging plays a key factor in ensuring the safety and preventing spoilage. Food packed in jars, cans ensures safety and prevents food from dust, moisture, air and harmful microbes.

Sources of Micro-organisms for Food Spoilage:

Micro-organisms are present everywhere. General source of Micro-organisms include air, water, sewage, soil and animal wastes. Foods grown in ground have higher risk of spoilage due to micro-organisms.  Foods like fish, meat are contaminated by presence of bacteria in their  internal organs like skin and feet. Meat has higher tendency of contamination as raw meat attracts lot of microbes, so it is advisable to store raw meet immediately after chopping.

Ways to Prevent Food Spoilage:

  • Ensure proper packaging is available to the food cans and jars after processing.
  •  Don’t leave the food in open air for more than 15min, to avoid contact with microbes.
  •  Ensure that your refrigerators are operating at correct temperatures.
  •  Food must be protected from light and must be stored in amber colour or transparent containers.
  • Low temperature is a key as it retards microbial growth.
  • Avoid placing food where there is more humidity, as high humidity attracts more growths of microbes and moulds. Placing food in dry places is most appropriate.


bacteria: reproduction and gene transfer


  • Binary fission
  • Transformation
  • Transduction
  • Conjugation

Reproduction and growth:

  • In unicellular organism cell growth and reproduction are two tightly linked processes unlike multicellular organism.
  • After gaining a fixed size bacteria reproduce through binary fission, budding and fragmentation.
  • Bacteria in optimum condition grow and divide rapidly and double its population in every 9.8 minutes.

Binary fission:

  • It is the most common mode of cell division and growth cycle of bacterial population.
  • In binary fission single cell divides into two identical cells with development of transverse septum (cross wall).
  • Two daughter cells contains nucleus of its own which is identical to the parent cell.
  • Cytoplasm divides leads to production of two equal sized cells.

Process of binary fission:

  • Before the division DNA in the bacterial cell is tightly coiled
  • DNA is then uncoiled and duplicated.
  • Each copy of the DNA is pulled to the separate poles.
  • Synthesis of new cell wall begins
  • Once the new cell wall is synthesised fully it results in complete split of bacterium.
  • New daughter cells now have tightly coiled DNA, plasmids and ribosomes.
Types of binary fissionExample

Gene transfer:

  • Gene transfer means movement of genetic information in organisms.
  • There are two types of gene transfer method one is vertical in which gene is transferred from parents to offspring and another one is horizontal in which gene is transferred in between two organisms.
  • In prokaryotes vertical gene transfer is by the means of binary fission and horizontal gene transfer method consist of three process i.e. transformation, transduction and conjugation.


  • In 1928 Fred Griffith discovered this method of horizontal gene transfer.
  • In this process naked DNA molecule or fragment from surrounding environment is uptake by the recipient and incorporated in its chromosome.
  • It is of two types natural and artificial, natural transformation is very rare event and observed in both gram negative and gram positive bacteria.
  • Ability of bacteria to uptake DNA fragment and get transformed is known as competence.

Process of transformation:

  • Competent bacteria naturally pull DNA fragment into their cell from the environment.
  • These DNA fragment naturally released in the environment after a bacterial cell die.
  • Ds DNA once crosses the membrane in cytoplasm the 3’ end is leading.
  • The translocated strand interested in the chromosome of recipient bacteria by homologous recombination.
  • Now the recipient bacteria undergoes replication and the cells acquired new phenotype are said to be transformed.


  • In transduction, DNA is transfer from donor bacteria to recipient bacteria by bacteriophage (functions as vector).
  • It was discovered by Lederberg and Zinder in 1951.
  • Bacteriophage due to high specificity of surface receptors has narrowest host range.
  • Transduction has one advantage over conjugation is that it doesn’t require physical contact of donor to recipient cell.
  • Transduction process is resistant to the DNase enzyme.


  • The phage infects the host and inserts its phage DNA into the cytoplasm of the host.
  • During lytic cycle the phage DNA along with the bacterial chromosome is broken down into pieces
  • Bacterial chromosome packed into the viral capsid is released by the lysis of the bacterium.
  • Now the transducing phage with bacterial chromosome is ready to infect another bacterium in this way donor’s DNA enters into the cytoplasm of second bacterium.
  • Host recombinase recA is present in the cell due to which donor DNA recombines with homologous bacterial DNA and produces transductants.


  • The process of transfer of plasmid or other transmissible DNA element from donor to recipient via sex pilus or conjugation tube.
  • Recipient of conjugation is known as transconjugants.
  • Is can transfer DNA regions of hundreds to thousands of kilobases and has board host range fro DNA transfer.
  • Occur in between many species of gram negative and gram positive bacteria even occurs between plants and bacteria.
  • Conjugation involves F plasmid is most common.


  • F+ structure contains tra locus which has pilin gene with some regulatory proteins responsible for the formation of pili on surface.
  • Proteins present on pili attach to the F- cell surface and responsible for making contact between them but doesn’t transfer plasmid.
  • The traD enzyme on the base of the pili makes the membrane to fuse.
  • After the conjugation initiated the enzyme relaxes attached to the conjugative plasmid and make  a nick at oriT.
  • The nicked strand is now transferred to the recipient cell
  • F+ cell carry such integrated F element is known as Hfr cell.
  • The F element of Hfr cell is replicated along with the bacterial chromosome and in this way transmitted from one to next generation.



  • Bacteria (singular bacterium) are unicellular microorganism which are of microscopic size and cannot be seen with unaided eyes.
  • Constitute large domain-prokaryotes.
  • They are among the first life form evolve on the earth and present in most of the habitat.
  • Bacteria inhabit normal to the extreme habitat like air, water, soil, radioactive waste, hot springs, deep seas, even in human gut, etc.
  • Also live in symbiotic and parasitic relationship with plants and animals. Example rhizobium associate with leguminous plants.
  • Length of bacteria ranges in few micrometres. E.coli (1.0-2.0 micrometre long and 0.5 micrometre in radius), Mycobacterium tuberculosis (2-4 micrometre long and 0.2-0.5 micrometre width), V cholerae (1-3 micrometre long and 0.5-0.8 micrometre radius).
  • The study of this discipline of microbiology is called bacteriology.
  • Bacteria are beneficial for human and other animals in a way that they produce various kind of vitamins, enzyme and food products. Example- vitamin B12, lactic acid, alcohol.
  • They are key components of our biosphere playing important role in biogeochemical cycles, removal of toxic substance and decomposition of waste materials.
  • Involve in nitrogen fixation hence improve soil fertility.
  • With beneficial characteristics several bacteria are pathogenic and cause various kind of disease in human, plants and animals. Example- cholera, tuberculosis, syphilis, anthrax, and more.
  • In industries bacteria are useful in waste water treatment and industrial fermentation for cheese and yogurt production.


  • Bacteria is a prokaryotic organism their body lacks nucleus and cellular components.
  • Bacteria are covered by a membrane called cell wall chiefly made up peptidoglycan (murein layer).
  • Peptidoglycan layer mainly constitute of polysaccharide which are cross linked by peptide bonds.
  • Peptidoglycan layer is made up of two glucose derivative N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) chain. The chain is linked with tertapeptide bonds
  • Four protein in tetrapeptide bond are L-alanine, D-alanine, L-lysine or meso-diaminopimelic acid (DPA) and D-glutamine.
  • Cell wall contributes to the survival of the bacteria, protection from harsh environment and antibiotics.
  • Peptidoglycan layer in gram positive bacteria is 20-80 nm thick in contrast gran negative bacteria contain 2-7 nm thick layer.
  • Gram negative bacteria contain acidic substance known as teichoic acids which provide rigidity to the cell wall.

Outer Membrane

  • Over the cell wall gram negative bacterium contain an external layer called outer membrane it contain lipopolysaccharide, phospholipids, lipoprotein and proteins.


  • It’s the carbohydrate enriched layer that covers the outside of the bacteria.
  • It provides protection against host
  • This glycocalyx layer associate with the pathogenic property to the bacteria.
  • Glycoclayx in a tightly packed form is called as capsule, in contrast in loose packing it is called as slime layer.

Surface Auxiliary


  • Hairlike structure, attach on the surface of the cell, main function is to provide mobility to the bacteria
  • Both gram positive and gram negative bacteria contain flagella. Consist of three parts filament, hook and basal body.


  • Thin hairlike structure on the surface of gram negative bacteria
  • Play an Important role in conjugation process


  • Present on both kind of cells gram negative an gran positive
  • Helps in attachment to the surface


  • Shape
Bacillus (Rod-Shaped)Escherichia coli (E. coli)
Coccus (Sphere)Streptococcus pneumoniae
Vibrio (Comma Shaped)Vibrio cholerae
Spirilla or spirochete (Spiral)Spirillum volutans
  • Mode of Nutrition
Autotrophic BacteriaPurple bacteria
Heterotrophic BacteriaAll disease-causing bacteria
  • Cell Wall
Gram positiveStaphylococcus aureus
Gram negativeEnterobacteriaceae
  • Mode of Respiration
AerobicPsuedomonas aeruginosa


  • The mode of replication in bacterium is binary fission.
  • In this process the parent bacterial cell divided into two identical daughter cells.
  • Replication of DNA starts in the parent cell and each copy is transfer into the daughter cell.
  • Rate of reproduction is depend on the conditions like temperature, nutrient availability, moisture this is called favourable condition. E.coli generation rate is 2 million bacteria in 7 hrs.
  • In some rare cases they undergo sexual reproduction by conjugation, transduction and transformation. Helps in genetic modification in bacteria which results in the antibiotic resistant property.