Pathogen profile of Klebsiella pneumoniae:

BY: SHAILY SHARMA (MSIWM041)

Klebsiella pneumoniae is the pathogen that causes pneumonia and septicemia (blood infections) which is usually found in the normal flora of the mouth skin and the intestines. It may also cause meningitis and bacteremia.

Normally when they occur in the intestines, the organism is harmless. However, the spreading of the organism to other parts pf the body and under certain conditions causes diseases in humans.

Clinically, it is one of the most significant members of the genus Klebsiella of the Enterobacteriaceae. In the recent years, one of the most important pathogens of the nosocomial infections, involving the urinary and the pulmonary systems, has been the Klebsiella species. 

Naturally, it occurs in the soil and about 30 percent of the strains of Klebsiella show nitrogen fixing abilities under anaerobic conditions.

• Microscopic morphology: 

• It is a gram-negative organism that occurs in the encapsulated form.
• It is a straight rod-shaped organism around 1 to 2 micrometers in length.
• It is a non-motile organism which is facultatively anaerobic.
• On MacConkey agar medium it appears as a mucoid lactose fermenter.

• Habitat:

• It is usually found in the mouth, skin and intestines of humans as normal flora.

• Virulence factors:

• The bacterium possesses a thick polysaccharide capsule which prevents the ingestion of the organism by the hosts phagocytes and somatic antigen from being detected by the host’s antibodies.
• The bacterium also shows the presence of a thick lipopolysaccharide capsule which makes the serum complement activation more difficult for the host’s immune system.
• K. pneumoniae protects itself and avoids damage by the host’s complement proteins by the extreme length of the molecules comprising the capsule and allows the membrane attack complex (MAC) to form away from the membrane. This helps in the prevention of opsonization and insertion of the MAC.
• The bacterium uses the host’s ferric-siderophore receptors to activate its own Enterobactin-mediated iron-sequestering system.

• Primary infections/disease:

• Most commonly, Klebsiella causes pneumonia. Typically, in the form of bronchopneumonia and bronchitis. 
• The organism is transmitted when a person is directly exposed to the bacteria. The bacteria must enter either directly enter the respiratory tract to cause pneumoniae or the blood stream to cause a bloodstream infection.
• These patients have a higher tendency to develop other complications like lung abscess, cavitation, empyema and pleural adhesions.
• Apart from or in addition to pneumonia, Klebsiella causes other infections like infections of the lower biliary tract, urinary tract and also infection of and around surgical wound sites. 
• The range of these clinical infections include diseases like cholecystitis, diarrhea, upper respiratory tract infection, meningitis, sepsis etc. 
• The bacterium can also enter the blood post sepsis and septic shock.
• In most cases, patients suffering from Klebsiella pneumoniae cough up a characteristic sputum in addition to fever, nausea, tachycardia, and vomiting.
• If a person acquires the infection in a community setting, like in a mall, community-acquired pneumonia occurs.
• A urinary tract infection (UTI) may also be caused by the pathogen if it enters one’s urinary tract. It typically occurs in older women.
• The pathogen may also cause wound infections like cellulitis, necrotizing fasciitis and myositis if it enters through a break in the skin and affects the soft tissue.

• Diagnosis:

• Susceptibility testing for (ESBL) Extended spectrum β-Lactamase.

• Other tests that can be done for the diagnosis of K. pneumoniae include:

1. CBC or complete blood count.
2. Sputum culturing of the patient.
3. Radiography of the chest to check for lung abnormalities visually.
4. CT scans.

• Treatment:

• The treatment for Klebsiella pneumoniae infections mainly depends upon the patient’s health conditions, medical history and the level of severity of the disease. 
• Treatment is by antibiotics like aminoglycosides and cephalosporins.

Sources: 

 Ryan, KJ; Ray, CG, eds. (2004). Sherris Medical Microbiology (4th ed.). McGraw Hill. ISBN 978-0-8385-8529-0.

 “Klebsiella species – GOV.UK”. www.gov.uk