Anaerobes

Gram Positive Bacilli: Spore Forming

Clostridium perfringens

  • Catalase negative

  • Box car shaped

  • Double zone beta hemolysis

  • Reverse CAMP

  • Vancomycin sensitive

  • Colistin resistant

  • Produces several exotoxins that destroy and disrupt host cells

  • Causes: gas gangrene, necrotizing fasciitis, food poisoning, necrotizing enteritis

Clostridium tetani

  • Subterminal spores

  • indoor positive

  • catalase negative

  • Vancomycin sensitive

  • Colistin resistant

  • Produces TeNT neurotoxin that disrupts impulses to muscles

  • Causes: tetanus (lockjaw)

Clostridium botulinum

  • Catalase negative

  • Subterminal spores

  • Vancomycin sensitive

  • Colistin resistant

  • Produces BoNT, a very potent neurotoxin that causes “rag doll” paralysis of essential muscle groups

  • Causes: botulism (foodborne, wound, intestinal, infant)

Clostridioides difficle

  • Produces toxin A (enterotoxin) and toxin B (cytotoxin), only strains that produce at least one of these toxins cause infection

  • Infection caused by decrease in normal gut flora (usually due to antibiotic usage)

  • Can progress into pseudomembrabous colitis ( surface of inflamed bowel becomes coated in necrotic debris, WBCs, and fibrin

Clostridium sordellii

  • Subterminal spores

  • Can swarm on brucellosis agar

  • Causes skin and soft tissue infections

Clostridium septicum

  • Stains poorly as it gets older

  • Subterminal spores

  • Swell cells

  • Swarms

  • Beta hemolytic

  • Irregular rhizome margins “Medusa head”

  • Causes bacteremia and trauma associated gangrene

Gram Positive Bacilli: Non-Spore Forming

Actinomyces spp

  • Filamentous branching rods

  • “Molar tooth” colonies

  • Vancomycin sensitive

  • Colistin resistant

  • Indole negative

  • Nitrate positive

  • Causes periodontal disease and soft tissue infections

Bifidobacterium

  • Gram positive diphtheroid, pointed or curved rods, branching, can have forked ends; “dog bones” or “Y” shaped

  • Usually found in mixed pelvic or abdominal infections

Cutibacterium acnes

  • Yellow, raised colonies

  • Gram positive rods, can look diphtheroid-like

  • Vancomycin sensitive

  • Colistin resistant

  • Indole positive

  • Nitrate positive

  • Catalase positive

  • Opportunistic pathogen

  • Common blood culture contaminant

Eubacterium

  • Gram positive pleomorphic rods/coccobacilli, can have beading, filaments, and branching

  • Causes oral infections, sinusitis, tonsillitis, and other various mixed infections

Lactobacillus

  • Gram positive pleomorphic rods/coccobacilli

  • Some species in this group are aerobic but some can also be anaerobic

  • Often a contaminant (usual vaginal flora)

  • Can cause sepsis in immunocompromised patients

Gram Positive Cocci

Peptostreptococcus asaccharolyticus

  • Indole positive

  • Catalase positive

  • Nitrate negative

  • Colistin resistant

  • Pairs, tetrads, or irregular clusters

Peptostreptococcus anaerobius

  • Indole positive

  • Catalase positive

  • Nitrate negative

  • Colistin resistant

  • Coccobacilli, chains

  • “Sweet rotting” odor

Gram Negative Bacilli

Bacteroides fragilis

  • Bile resistant

  • Colistin resistant

  • Vancomycin resistant

  • Indole negative

  • Nitrate negative

  • Catalase positive

  • Black on BBE agar

  • Most common cause of anaerobic infections

Biophilia spp

  • Pale staining, delicate gram negative rods

  • After 3-5 days on BBE agar, colonies can have a black center that may disappear when exposed to O2

  • Causes intra-abdominal infections and abscesses

Prevotella spp

  • Pigmented and non-pigmented varieties

  • Bile sensitive

  • Kanamycin resistant

  • Vancomycin resistant

  • Catalase negative

  • Indole negative

  • Normal flora of the oral cavity

  • Pigmented Prevotella will have brick red fluorescence and be black on LKV agar

Porphyromonas spp

  • P. gingivalis is most common in this group

  • Gram negative coccobacilli

  • Dark brown to black pigmented colonies, fluoresces brick red

  • Indole positive

  • Nitrate negative

  • Catalase negative

  • Kanamycin resistant

  • Colistin resistant

  • Vancomycin sensitive

  • Bile sensitive

Fusobacterium necrophorum

  • Most virulent fusobacterium species

  • Gram negative, pale staining, slender spindle shaped rods, pointed ends, can be filamentous

  • Fluoresces chartreuse

  • Indole positive

  • Nitrate negative

  • Catalase negative

  • Kanamycin sensitive

  • Colistin sensitive

Fusobacterium nucleatum

  • Gram negative, pale staining, slender spindle shaped rods, pointed ends

  • Bread crumb-like colony

  • Fluoresces chartreuse

  • Causes head/neck and pleuro-pulmonary infections

Fusobacterium mortiferum

  • Gram negative, pale staining, filamentous rods, with swollen areas

  • “Fried egg” colony

  • Causes various infections, oral, bacteremia, etc

  • Indole negative

Mobiluncus spp

  • Normal vaginal flora but can cause bacterial vaginosis

  • Gram variable, small, thin, curved rods

  • Very small colonies

Villanelle spp

  • Rarely significant but can be found in mixed infections

  • Tiny gram negative diplodocus in clusters, pairs, and chains