Spirochetes

Characteristics: Gram-negative, periplasmic flagella, helically-coiled

Examples: Treponema pallidum (syphilis), Borrelia burgdorferi (Lyme disease)

Pseudomonads

Characteristics: Gram-negative aerobic rods, may live in soil or water, infect wounds and burns

Examples: P. aeruginosa, P. marginalis

Nitrogen-Fixers

Characteristics: Gram-negative aerobic rods, fix nitrogen, may be free-living or symbiotic

Examples: Azotobacter (free-living), Rhizobium (symbiotic)

Helicobacter

Characteristics: Gram-negative aerobic rods, microaerophilic, sheathed flagella, urease activity

Examples: H. pylori (gastritis, stomach ulcers and cancer)

Neisseria

Characteristics: Gram-negative aerobic cocci, animal pathogens

Examples: N. gonorrhoeae, N. meningitidis

Brucella

Characteristics: Gram-negative aerobic cocci, causes abortion in cattle

Examples: None provided

Methyl bacteria

Characteristics: Gram-negative aerobic cocci, can use methane or methanol as sole carbon source

Examples: None provided

Escherichia coli

Characteristics: Gram-negative facultatively anaerobic rod, naturally occurs in the human gut, opportunistic pathogen, diverse number of strains, endotoxins and exotoxins are strain-dependent 

Examples: N/A

Salmonella

Characteristics: Gram-negative facultatively anaerobic rod

Examples: S. typhimurium (gastroenteritis), S. typhi (typhoid fever)

Shigella dysenteriae

Characteristics: Gram-negative facultatively anaerobic rod, causes dysentery

Examples: N/A

Yersinia pestis

Characteristics: Gram-negative facultatively anaerobic rod, causes the bubonic plague

Examples: N/A

Serratia

Characteristics: Gram-negative facultatively anaerobic rod

Examples: N/A

Proteus

Characteristics: Gram-negative facultatively anaerobic rod

Examples: N/A

Haemophilus

Characteristics: Gram-negative facultatively anaerobic rod

Examples: N/A

Rickettsiae

Characteristics: Gram-negative obligate intracellular parasite, extremely small, complex life cycles

Examples: Rickettsia (RMSF), Chlamydia, Coxiella (Q fever)

Staphylococcus

Characteristics: Gram-positive coccus

Examples: S. aureus (TSS), S. epidermidis

Streptococcus

Characteristics: Gram-positive coccus

Examples: S. pyogenes (major human pathogen), S. mutans (dental decay), S. pneumoniae (bacterial pneumonia)

Enterococcus

Characteristics: Gram-positive coccus, clinically important as it causes UTI's, bacteremia, bacterial endocarditis, diverticulitis, and meningitis

Examples: None provided

Bacilli

Characteristics: Gram-positive endospore-forming rods, aerobic, chemoheterotrophic, flagellated and motile, antibiotics

Examples: B. anthracis, B. subtilis (soil organism), B. cereus (food poisoning), B. thuringiensis (insect toxins) 

Clostridium

Characteristics: Gram-positive endospore-forming rods, anaerobic

Examples: C. perfringens (gas gangrene), C. tetani, C. botulinum, C. acetobutylicum (produces acetic acid, ethanol, and benzene), C. butyricum (produces butyric acid in butter and cheese) 

Mycobacteria

Characteristics: Cell wall-less, pleomorphic, parasitic, requires sterols from host, related to gram-positive rods

Examples: Mycoplasma pneumoniae

Cyanobacteria

Characteristics: Gram-negative, oxygenic, all species evolved from a common ancestor

Examples: Nostoc, Anabaena, Prochlorococcus (produces most of the Earth's oxygen)

Actinomycetes

Characteristics: Gram-positive, spore-forming, mycelia, fungal-like soil organisms, source of many antibiotics

Examples: None provided

Archaea

• More common than previously thought
• May account for more than half of all bacterial diversity
• Include extreme thermophiles, extreme halophiles, and methanogens