Obligate aerobic

Gram-negative cocci

Moraxella catarrhalis, Neisseria gonorrhoeae, N. meningitidis*

Gram-positive bacilli

Corynebacterium jeikeium

Acid-fast bacilli

Mycobacterium avium complex, M. kansasii, M. leprae, M. tuberculosis, Nocardia species

Nonfermentative, non-Enterobacterales (formerly Enterobacteriaceae)

Acinetobacter calcoaceticus, Elizabethkingia meningoseptica (formerly Flavobacterium meningosepticum), Pseudomonas aeruginosa,* P. alcaligenes, other Pseudomonas species, Stenotrophomonas maltophilia

Fastidious gram-negative coccobacilli and bacilli

Brucella, Bordetella, Francisella, and Legionella species

Leptospiraceae (spiral bacteria)

Leptospira species

Obligate anaerobic

Gram-negative bacilli

Bacteroides fragilis, other Bacteroides species, Fusobacterium species, Prevotella species

Gram-negative cocci

Veillonella species

Gram-positive cocci

Peptococcus niger, Peptostreptococcus species

Non–spore-forming gram-positive bacilli

Actinomyces, Bifidobacterium, Eubacterium, and Cutibacterium (formerly Propionibacterium) species

Endospore-forming gram-positive bacilli

Clostridium botulinum, C. perfringens, C. tetani, other Clostridium species

Facultative anaerobic

Gram-positive cocci, catalase-positive

Staphylococcus aureus (coagulase-positive), S. epidermidis (coagulase-negative), other coagulase-negative staphylococci

Gram-positive cocci, catalase-negative

Enterococcus faecalis, E. faecium, Streptococcus agalactiae (group B streptococcus), S. bovis, S. pneumoniae, S. pyogenes (group A streptococcus), viridans group streptococci (S. mutans, S. mitis, S. salivarius, S. sanguis), S. anginosus group (S. anginosus, S. milleri, S. constellatus), Gemella morbillorum

Gram-positive bacilli

Bacillus anthracis, Erysipelothrix rhusiopathiae, Gardnerella vaginalis (gram-variable)

Gram-negative bacilli

Enterobacterales (Citrobacter species, Enterobacter species, Escherichia coli, Klebsiella species, Morganella morganii, Proteus species, Plesiomonas shigelloides, Providencia rettgeri, Salmonella typhi, other Salmonella species, Serratia marcescens, Shigella species, Yersinia enterocolitica, Y. pestis)

Fermentative, non-Enterobacterales

Aeromonas hydrophila, Chromobacterium violaceum, Pasteurella multocida

Fastidious gram-negative coccobacilli and bacilli

Aggregatibacter (formerly Actinobacillus) actinomycetemcomitans, Eikenella corrodens, Haemophilus influenzae, other Haemophilus species

Mycoplasma

Mycoplasma pneumoniae

Microaerophilic

Curved bacilli

Campylobacter jejuni, Helicobacter pylori, Vibrio cholerae, V. vulnificus

Spirochaetaceae (spiral bacteria)

Borrelia burgdorferi, Treponema pallidum

Obligate intracellular parasitic

Chlamydiaceae

Chlamydia trachomatis, Chlamydophila pneumoniae, C. psittaci

Coxiellaceae

Coxiella burnetii

Rickettsiales

Rickettsia prowazekii, R. rickettsii, R. typhi, Orientia tsutsugamushi, Ehrlichia chaffeensis, Anaplasma phagocytophilum