Anaerobes of Clinical Importance

Part Two

MLAB 2434 – Microbiology Keri Brophy-Martinez

Frequently Encountered Anaerobes

• Gram-positive spore-forming anaerobic bacilli– Clostridium• Epidemiology

– Normal flora of lower intestinal tract– Found in soil– Most from exogenous sources

ClostridiumPathogenicity

• Botulism– Agent: Clostridium botulinum– Spread: veggies, mushrooms, fish, honey– Toxin: neurotoxin acts on neuromuscular junctions of

peripheral nervous system causing neuroparalytic illness– Clinical Forms: foodborne, wounds– Clinical Features: Symmetrical, descending weakness or

paralysis; floppy baby syndrome; clear mental status– Diagnosis: collect serum and feces to demonstrate toxin– Prevention: adequate canning and cooking of foods

ClostridiumPathogenicity

• Gas gangrene (myonecrosis)– Agent: Clostridium perfringens– Spread: contamination of wounds– Clinical features: Muscle becomes

necrotic; contains gas– Lab Diagnosis: boxcar-shaped gpr,

double zone of beta-hemolysis

ClostridiumPathogenicity

• Tetanus– Agent: Clostridium tetani– Spread: skin penetration by contaminated

materials or surgery– Toxin: tetanospamin acts on CNS to produce

prolonged muscle spasms– Clinical features: Muscle spasm,

hyperexcitability, odd facial expressions– Lab Diagnosis: Gpr with oval, terminal or

subterminal spores, gives a “drumstick” or “tennis racket” appearance

– Prevention: immunization

ClostridiumPathogenicity

• Pseudomembranous colitis– Agent: Clostridium difficile– Spread: nosocomial infection– Critical factors for disease to occur: normal bowel flora

disruption, organism must be toxin producing– Toxin: toxin A(enterotoxin) Toxin B(cytotoxin)– Clinical features: diarrhea, inflammation of bowel, bowel

is necrotic (see WBC’s and fibrin forming a pseudomembrane)

– Lab diagnosis: C. difficle is most often detected via by EIA or PCR

Gram-positive non-spore-forming anaerobic bacilli

• Most are from endogenous sources and are therefore opportunists– Propionibacterium

• Epidemiology– Normal skin flora

• Pathogenicity– Seen as a contaminant in blood cultures– Causes acne – May cause subacute bacterial endocarditis and

bacteremia– Affinity for medical devices

Propionibacterium:Lab Diagnosis

• Coccoid, club-shaped or branched morphology– Chinese letters

• Microaerotolerant• Catalase positive• Indole positive• Reduces nitrate

Actinomyces species

– Epidemiology• Normal flora in mouth, head, neck, GI tract, female

genital tract, and upper respiratory system.• Pathogenicity

– Eye Infections– Cervicitis and endometritis in women using IUD’s– Actinomycosis (head and neck infections)

• Lab Diagnosis– Short to filamentous, branching rod; can be beaded;

may see sulfur granules on direct specimen exam– Molar tooth appearance on media; slow grower;

fastidious

Actinomyces

Gram-positive non-spore-forming anaerobic bacilli

• Bifidobacterium• Eggerthella/Eubacterium• Lactobacillus

Gram Negative Non-spore formers- Anaerobic Cocci

• Veillonella– Epidemiology• Normal flora in mouth, upper respiratory

tract, GI tract and vagina

– Pathogenicity• Associated with peridontal and soft tissue

infections of the mouth, bite wounds, head, neck and pulmonary infections

Gram Positive, Non-Spore Formers- Anaerobic Cocci

• Peptostreptococcus species

– Epidemiology• Normal flora in mouth, skin, genitourinary and GI

tracts

– Pathogenicity• Can cause any type of infection

Gram-negative Non-spore Formers- Anaerobic Bacilli

• Bacteroides fragilis group– Epidemiology• Normal flora of mouth, URT, intestinal tract,

urogenital tract

– Pathogenicity• Wounds, abscesses in body sites below the

diaphragm• Bacteremia

Bacteroides fragilis group:Lab Diagnosis

• Pale staining, pleomorphic rod with rounded ends; safety pin appearance

• Look for growth on BBE, see esculin hydrolysis around the colony, precipitated bile

• Can use antibiotic disk, GLC for Id

Porphyromonas spp.

• Epidemiology

– Normal flora of mouth, URT, intestinal tract and urogential tract

• Pathogenicity• Assocaited with opportunistic infections• Soft tissue infection below waist

• Lab Diagnosis• Red fluorescence under UV light• Black pigmented colonies on KV• Can use antibiotic disks to id

Prevotella spp.

• Epidemiology• Normal flora of mouth, URT, intestinal tract,

urogenital tract• Pathogenicity– Peridontitis– Head and neck and pleuropulmonary infections

• Lab diagnosis– GNR is short chains or pairs– KV media see black pigment– Can use antibiotic disk for id

Fusobacterium Spp.

• Epidemiology• Normal flora of mouth, URT, intestinal tract,

urogenital tract• Pathogenicity– Respiratory tract– Head and neck infections

• Lab diagnosis– GNR is long, thin, fusiform, and pleomorphic– Do not grow well on KV– Can use antibiotic disk for id

References

• http://www.labsupplyoutlaws.com/products/Lab-Equipment/Microbiology-Apparatus/Environmental-Systems-for-Microbiology/BD-BBL-Bio-Bag-Environmental-Chambers.htm

• Kiser, K. M., Payne, W. C., & Taff, T. A. (2011). Clinical Laboratory Microbiology: A Practical Approach . Upper Saddle River, NJ: Pearson Education.

• Mahon, C. R., Lehman, D. C., & Manuselis, G. (2011). Textbook of Diagnostic Microbiology (4th ed.). Maryland Heights, MO: Saunders.