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
Clostridium
Pathogenicity
• 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
Clostridium
Pathogenicity
• 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
Clostridium
Pathogenicity
• 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
Clostridium
Pathogenicity
• 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/LabEquipment/Microbiology-Apparatus/Environmental-Systems-forMicrobiology/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.