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Bacterial classification

Genus Important species Gram staining Shape Capsulation Bonding tendency Motility Respiration Growth medium Intra/Extracellular
Bordetella Gram-negative Small coccobacilli Encapsulated singly or in pairs
aerobic Regan-Lowe agar extracellular
Borrelia Gram-negative, but stains poorly

Long, slender, flexible, spiral- or corkscrew-shaped rods highly motile
(difficult to culture) extracellular
Brucella Gram-negative Small coccobacilli Unencapsulated singly or in pairs
aerobic Blood agar intracellular
Campylobacter Gram-negative Curved, spiral, or S-shaped
with single, polar flagellum

characteristic darting motion microaerophilic Blood agar inhibiting other fecal flora extracellular
Chlamydia and Chlamydophila (not Gram-stained) Small, round, ovoid

motile Facultative or strictly aerobic
Obligate intracellular
Clostridium Gram-positive Large, blunt-ended rods

mostly motile Obligate anaerobic Anaerobic blood agar extracellular
Corynebacterium Gram-positive (unevenly) Small, slender, pleomorphic rods unencapsulated clumps looking like Chinese characters or a picket fence nonmotile Mostly facultative anaerobic Aerobically on Tinsdale agar extracellular
Enterococcus Gram-positive Round to ovoid
pairs or chains
Facultative Anaerobic 6.5% NaCl, bile-esculin agar extracellular
Escherichia Gram-negative Short rods

Facultative anaerobic MacConkey agar extracellular
Francisella Gram-negative Small, pleomorphic coccobacillus

strictly aerobic (rarely cultured) Facultative intracellular
Haemophilus Gram-negative Ranging from small coccobacillus to long, slender filaments

Chocolate agar with hemin and NAD+ extracellular
Helicobacter Gram-negative Curved or spiral rods
pultiple polar flagella

rapid, corkscrew motility
Medium containing antibiotics against other fecal flora extracellular
Legionella Gram-negative, but stains poorly Slender rod in nature, cocobacillary in laboratory.
monotrichious flagella
Specialized medium facultative intracellular
Leptospira Gram-negative, but stains poorly Long, very slender, flexible, spiral- or corkscrew-shaped rods

highly motile
Specialized medium extracellular
Listeria Gram-positive, darkly Slender, short rods
diplobacilli or short chains Distinct tumbling motility in liquid medium
enriched medium intracellular
Mycobacterium (none) Long, slender rods

nonmotile aerobic M. tuberculosis: Lowenstein-Jensen agar
M. leprae: (none)
Mycoplasma (none) Plastic, pleomorphic
singly or in pairs

(rarely cultured) extracellular
Neisseria Gram-negative Kidney bean-shaped
aerobic Thayer-Martin agar Gonococcus: facultative intracellular
N. meningitidis
: extracellular
Pseudomonas Gram-negative rods encapsulated
motile Obligate aerobic MacConkey agar extracellular
Rickettsia Gram-negative, but stains poorly Small, rod-like coccobacillary

(rarely cultured) Obligate intracellular
Salmonella Gram-negative

Facultative anaerobic MacConkey agar Facultative intracellular
Shigella Gram-negative rods

Facultative anaerobic Hektoen agar extracellular
Staphylococcus Gram-positive, darkly Round cocci
in bunches like grapes
Facultative anaerobic enriched medium (broth and/or blood) extracellular
Streptococcus Gram-positive ovoid to spherical
pairs or chains nonmotile Facultative anaerobic blood agar extracellular
Treponema Gram-negative, but stains poorly Long, slender, flexible, spiral- or corkscrew-shaped rods

highly motile
none extracellular
Vibrio Gram-negative Short, curved, rod-shaped with single polar flagellum

rapidly motile Facultative anaerobic blood- or MacConkey agar. Stimulated by NaCl extracellular
Yersinia Gram-negative, stains bipolarly Small rods encapsulated
nonmotile Facultative Anaerobe MacConkey or CIN agar extracellular