High-Yield Levinson: Bacterial Classification & Normal Flora (MBBS)

Bacteria classification



1. Classification by morphology or shape
a. Cocci
i. Round/spherical
ii. Diplococci (pairs)
iii. Streptococci (chains)
iv. Grapelike clusters (staphylococci)
b. Bacilli
i. Rod shaped
c. Spirochetes:
i. Spiral-shaped
d. Pleomorphic:
i. Variable shape
2. Classification by gram staining:
a. Gram positive
i. Thick, multilayered peptidoglycan cell wall
ii. Stain blue/purple
b. Gram negative
i. Thin peptidoglycan layer
ii. Outer lipid rich membrane
iii. Take up the counterstain after losing the initial stain
iv. Appear red or pink
c. Non-staining
i. Mycobacteria have high lipid concentrations in cell walls.
Must use acid fast stain
ii. Mycoplasma lacks cell wall
iii. T. pallidum is too thin to be seen
iv. Chlamydiae is small intracellular organism
3. Classification by respiratory method:
a. Obligate aerobes:
i. Require oxygen to grow
ii. ATP generating systems depend on it as hydrogen
acceptor.
b. Facultative anaerobes:
i. Generate energy using oxygen if it is present
ii. Can also use fermentation in the absence of oxygen
c. Obligate anaerobes:
i. Cannot grow in presence of oxygen