CLASSIFICATION OF BACTERIA

Content:

• Classification based on morphology of bacteria
• Anatomical Based Classification
• Classification Based On Staining
• Classification Based Of Cultural Characteristics
• Classification Based On Environmental Factors

• Largest bacteria- Thiomargarita namibiensis
• Longest bacteria- Epulopiscium fishelsoni
• smallest bacteria- Mycoplasma genitalium

Classification Based On Morphology Of Bacteria:

• Cocci: spherical shape, classified on the basis of arrangement

Types	Example
Monococci	Monococcus
Diplococci	Streptococcus pneumonia
Staphylococci	Staphylococcus aureus
Streptococci	Streptococcus pyogenes
Tetrad	Micrococcus
Octard	sarcinae

• Bacilli: rod shaped, classified on the basis of arrangement

Types	Example
Diplobacilli	Moraxella bovis
Streptobacilli	Streptobacillus moniliformis
Palisades	Corynebacterium diphtheria
Chinese-letter form	Corynebacterium glutamicum
Coccobacilli	Gardnerella vaginalis

• Actinomycetes: they are bacteria but resemble fungi by exhibiting branching

Example: Actinomyces israeli

• Spirochetes: these are spiral shaped long, slender, non- branched microorganism.

Example: Borrelia burgdorferi

• Mycoplasma: lack rigid cell wall and are highly pleomorphic.

Example: ‎Mycoplasma pneumonia

• Rickettsiae and Chlamydiae: they are small and obligate parasite.

Example: Chlamydiae psittaci, Rickettsia rickettsii

Anatomical Based Classification:

• Capsule:

Type	Example
Capsulate	Streptococcus pneumonia
Non-capsulate	Viridans streptococci

• Flagellate:

Type	Example
Monotrichous	Vibrio cholerae
Lophotrichous	Pseudomonas fluorescens
Amphitrichous	rhodospirillum rubrum
Peritrichous	E. coli

• Aflagellate: shigella spp.
• Spore:

Type	Example
Spore-forming	Bacillus spp.
Non-sporing	Escherichia coli

Classification Based On Staining:

• Gram’s stain:

Types	Example
Gram-positive cocci	Staphylococcus aureus
Gram-negative cocci	Nesseria gonorrhoeae
Gram-positive rods	Clostridium
Gram-negative rods	Enterobacteriaceae

• Acid-fast stain:

Types	Example
Acid-fast bacilli	Mycobacterium tuberculosis
Non acid-fast bacilli	Salmonella typhi

Classification Based Of Cultural Characteristics:

• Extra growth factors requirements:

Type	Example
Fastidious	Hemophilus influenza
Non-fastidious	Esherichia coli

• Hemolysis on sheep blood agar:

Types	Example
Alpha-hemolysis	Streptococcus pneumonia
Beta-hemolysis	Streptococcus pyogenes
Gamma-hemolysis	Staphylococcus saprophyticus
Alpha-prime hemolysis	Streptococcus pyogenes

• Utilization of carbohydrates:

Types	Example
Oxidative	Micrococcus
Fermentative	Escherichia coli

• Growth rate:

Types	Example
Rapid growers	Vibrio cholera
Slow growers	Mycobacterium tuberculosis

• Pigment production:

Types	Example
Pigment producer	Staphylococcus aureus
Pigment non-producer	Escherichia coli

Classification Based On Environmental Factors:

• Temperature:

Types	Example
Psychrophiles(15-20o C)	Pseudomonas fluorescens
Mesophiles (20-40o C)	Salmonella enterica
Thermopiles (50-60o C)	Bacillus stearothermophillus
Extremely thermophiles (as high as 250o C)	Pyrococcus furiosus

• Oxygen:

Types	Example
Aerobe	Streptococcus spp.
Obligate aerobes	Pseudomonas aeruginosa
Microaerophilic	Campylobacter jejuni
Facultative anaerobe	E. coli
Obligate anaerobe	Clostridium
Capnophilic	N. gonorrhoeae
Aerotolerant	Streptococcus

• pH:

Types	Example
Acidophiles (pH less than 3)	Lactobacillus acidophilus
Alkaliphiles (pH roughly 8.5-11)	Vibrio
Neutralophiles (pH 6.5-8)	Pseudomonas aeruginosa

• Salt concentration:

Non-halophiles: cannot grow in high salt concentration

Example: E. coli

Halotolerant: Can tolerate low level upto 8% of salt concentration

Example:

Halophiles: can grow in high salt concentration

Types	Example
Slightly halophilic (require 0.5-3% concentration)	Vibrio, pseudomonas
Moderately halophilic (requires 3-15% conc)	Bacillus
Extremely halophilic (requires 15-30% conc)	halococcus

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