13 – Non-Spore-Forming Anaerobes Flashcards
Microbiological characteristics
- Gram negative, obligate anaerobes
- Involved in necrotic and suppurative conditions
- Often polymicrobial
- May require special skills in handling anaerobes to culture
- *stinky
Examples of non-spore-forming anaerobes
- Fusobacterium
- Dichelobacter
- Prevotella
- Bacteroides
Fusobacterium: on plate
- Long, slender pleomorphic Gram-negative rods
Dichelobacter nodosus: on plate
- Straight or slightly curved with swellings at both ends
Prevotella spp.: on plate
- Rounded ends
Fusobacterium: natural host or habitat
- Lives in GIT
- *lots in rumen contents of cattle
Dichelobacter nodosus: natural host or habitat
- Primary resident of ruminant foot
Prevotella spp.: natural host or habitat
- Resident of mouth of variety species (including people)
Natural host or habitat
- Opportunistic pathogens
- Become problematic when
o Gain entry to normally sterile sites
o Tissues become ischemic
Fusobacterium necrophorum: virulence factors
- Leukotoxin
o Lysis of bovine leukocytes and toxic for hepatocytes
Dichelobacter nodosus: virulence factors
- Type IV fimbriae: motility and adherence
- Serine proteases: degradation of hoof proteins
F. necrophorum in cattle
- Often associated with Trueperlla pyogenes
- Several presentations
o Calf diphtheria
o Liver abscesses
o Metritis in dairy cows
o Interdigital necrobacillosis (“foul of the foot”)
F. necrophorum: calf diphtheria
- Necrotic foci on larynx, trachea, and buccal cavity
- Abrasions of pharynx due to rough feed provide portal for entry
- Fever, depression, excessive salivation
- Foul smell
- Progresses to fatal pneumonia if untreated
F. necrophorum: liver abscess in feedlot cattle
- Septic embolism following rumenitis
F. necrophorum: interdigital necrobacillosis (“foul of the foot”)
- Often associated with:
o Trueperella pyogenes
o Porphyromonas levii
o Dichelobacter nodosus
F. necrophorum cytology
- thin irregularly staining
Dichelobacter nodosus in sheep
- Contagious foot rot (ovine digital dermatitis)
o Also involves F. necrophorum - Lameness
- Doesn’t readily survive in environment primary reservoir=infected sheep
- Associated with warm, wet conditions
Dichelobacter nodosus: Primary reservoir=infected sheep
- Transmission via transiently contaminated environments
o Trucks, paddocks
Dichelobacter nodosus: ‘steps’
- Damage to tissue
a. Interdigital skin is delicate, can become mascerated when wet - Initial invasion by F. necrophorum
a. Superficial infection and inflammation - D. nodous arrives
a. Proliferates in F. necrophorum lesion
b. Produces proteases which detach horn from underlying tissues
Specimens to collect
- Purulent material from abscesses
- Discharges
- Tissue specimens
Sample handling
- Anaerobic swabs are a MUST!
o Sterile swab with oxygen scavenging sachet - Larger tissue ‘chunks’ can maintain anaerobic microenvironments
Lab ID
- Smears of affected tissues can be helpful
- Anaerobic culture
- ID of suspect pathogens by PCR
- *antimicrobial susceptibility testing of anaerobes is POORLY standardized
Lab ID ‘materials’ needed
- Anaerobic jar
- Gas-pack (O2 scavenging sachet)
- Anaerobic indicator strip (white=anaerobic, blue=aerobic)
- Pre-reduced media (dull colour blood agar plates_
Zoonotic/interspecies transmission
- None are recognized as great concern
o Fusobacterium species are normal members of respiratory, GI and genitourinary systems of people - *isolate Fusobacterium, Porphyromonas and Prevotella have been isolated in cat and dog bites
Streptobacillus moniliformis: rat-bite fever
- Found in rodents
- 7-10 day incubation period
- People at risk include
o Those working with animals
o Homeless people exposed to urban rats
7-10 day incubation period of Streptobacillus moniliformis: rat-bite fever
- Abrupt onset of fever, chills, headache and vomiting
- 50% then develop macropapular rash
- Systemic spread, bacteremia, endocarditis may occur
- *may resemble Rocky Mountain Spottle Fever (stay tuned)
Macropapular
- Cutaneous eruption of both macules (altered in colour but not raised) and papules (small, solid, conical elevation of skin)
Capnocytophaga canimorsus
- Gram-negative rods
- Slow growing and fastidious
- Carboxyphilic (‘capno’)
- Found in mouths of dogs and cats (80+%)
- Also in humans mouths
Capnocytophaga canimorsus: infections in people following dog (or cat) bites
- most common in older and immunocompromised people
- *particularly splenectomised
- Mortality rate up to 30%
- No risk factors ID in 40% of cases
- Antimicrobials are critical! (vancomycin, penicillins)
Following phagocytosis: Capnocytophaga canimorsus
- Continues to replicate and kill host cell
Capnocytophaga canimorsus: truck driver with a dog that always licked his face
- Previously splenectomized
- Extremely sick: pyrexic, tachypnic, severe abdominal pain
Treatment options
- Depends on site of infection
- Foot rot: combination of systemic antimicrobials and topical antiseptics
o Different animal sensitivities to topical agents (ex. sheep and Cu)
Drugs to avoid/intrinsic resistance: F. necrophorum
- Penicillin susceptible
- Other species often resistant
Drugs to avoid/intrinsic resistance: Bacteroides spp.
- Resistant to penicillin and colistin
Drugs to avoid/intrinsic resistance: Capnocytophaga
- Avoid sulfonamides and aminoglycosides
Control
- Management practices important
o Dietary management
o Paddock and pasture management to keep feet dry/clean
