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
TypesExample
MonococciMonococcus
DiplococciStreptococcus pneumonia
StaphylococciStaphylococcus aureus
StreptococciStreptococcus pyogenes
TetradMicrococcus
Octardsarcinae
  • Bacilli: rod shaped, classified on the basis of arrangement
TypesExample
DiplobacilliMoraxella bovis
StreptobacilliStreptobacillus moniliformis
PalisadesCorynebacterium diphtheria
Chinese-letter formCorynebacterium glutamicum
CoccobacilliGardnerella 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:
TypeExample
CapsulateStreptococcus pneumonia
Non-capsulateViridans streptococci
  • Flagellate:
TypeExample
MonotrichousVibrio cholerae
LophotrichousPseudomonas fluorescens
Amphitrichousrhodospirillum rubrum
PeritrichousE. coli
  • Aflagellate: shigella spp.
  • Spore:
TypeExample
Spore-formingBacillus spp.
Non-sporingEscherichia coli

Classification Based On Staining:

  • Gram’s stain:
TypesExample
Gram-positive cocciStaphylococcus aureus
Gram-negative cocciNesseria gonorrhoeae
Gram-positive rodsClostridium
Gram-negative rodsEnterobacteriaceae
  • Acid-fast stain:
TypesExample
Acid-fast bacilliMycobacterium tuberculosis
Non acid-fast bacilliSalmonella typhi

Classification Based Of Cultural Characteristics:

  • Extra growth factors requirements:
TypeExample
FastidiousHemophilus influenza
Non-fastidiousEsherichia coli
  • Hemolysis on sheep blood agar:
TypesExample
Alpha-hemolysisStreptococcus pneumonia
Beta-hemolysisStreptococcus pyogenes
Gamma-hemolysisStaphylococcus saprophyticus
Alpha-prime hemolysisStreptococcus pyogenes
  • Utilization of carbohydrates:
TypesExample
OxidativeMicrococcus
FermentativeEscherichia coli
  • Growth rate:
TypesExample
Rapid growersVibrio cholera
Slow growersMycobacterium tuberculosis
  • Pigment production:
TypesExample
Pigment producerStaphylococcus aureus
Pigment non-producerEscherichia coli

Classification Based On Environmental Factors:

  • Temperature:
TypesExample
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:
TypesExample
AerobeStreptococcus spp.
Obligate aerobesPseudomonas aeruginosa
MicroaerophilicCampylobacter jejuni
Facultative anaerobeE. coli
Obligate anaerobeClostridium
CapnophilicN. gonorrhoeae
AerotolerantStreptococcus
  • pH:
TypesExample
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

TypesExample
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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