13 – Non-Spore-Forming Anaerobes

Question 1

Microbiological characteristics

Answer 1

• Gram negative, obligate anaerobes
• Involved in necrotic and suppurative conditions
• Often polymicrobial
• May require special skills in handling anaerobes to culture
• *stinky

Question 2

Examples of non-spore-forming anaerobes

Answer 2

• Fusobacterium
• Dichelobacter
• Prevotella
• Bacteroides

Question 3

Fusobacterium: on plate

Answer 3

• Long, slender pleomorphic Gram-negative rods

Question 4

Dichelobacter nodosus: on plate

Answer 4

• Straight or slightly curved with swellings at both ends

Question 5

Prevotella spp.: on plate

Answer 5

• Rounded ends

Question 6

Fusobacterium: natural host or habitat

Answer 6

• Lives in GIT
• *lots in rumen contents of cattle

Question 7

Dichelobacter nodosus: natural host or habitat

Answer 7

• Primary resident of ruminant foot

Question 8

Prevotella spp.: natural host or habitat

Answer 8

• Resident of mouth of variety species (including people)

Question 9

Natural host or habitat

Answer 9

• Opportunistic pathogens
• Become problematic when
  o Gain entry to normally sterile sites
  o Tissues become ischemic

Question 10

Fusobacterium necrophorum: virulence factors

Answer 10

• Leukotoxin
  o Lysis of bovine leukocytes and toxic for hepatocytes

Question 11

Dichelobacter nodosus: virulence factors

Answer 11

• Type IV fimbriae: motility and adherence
• Serine proteases: degradation of hoof proteins

Question 12

F. necrophorum in cattle

Answer 12

• 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”)

Question 13

F. necrophorum: calf diphtheria

Answer 13

• 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

Question 14

F. necrophorum: liver abscess in feedlot cattle

Answer 14

• Septic embolism following rumenitis

Question 15

F. necrophorum: interdigital necrobacillosis (“foul of the foot”)

Answer 15

• Often associated with:
  o Trueperella pyogenes
  o Porphyromonas levii
  o Dichelobacter nodosus

Question 16

F. necrophorum cytology

Answer 16

• thin irregularly staining

Question 17

Dichelobacter nodosus in sheep

Answer 17

• 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

Question 18

Dichelobacter nodosus: Primary reservoir=infected sheep

Answer 18

• Transmission via transiently contaminated environments
  o Trucks, paddocks

Question 19

Dichelobacter nodosus: ‘steps’

Answer 19

1. Damage to tissue
   a. Interdigital skin is delicate, can become mascerated when wet
2. Initial invasion by F. necrophorum
   a. Superficial infection and inflammation
3. D. nodous arrives
   a. Proliferates in F. necrophorum lesion
   b. Produces proteases which detach horn from underlying tissues

Question 20

Specimens to collect

Answer 20

• Purulent material from abscesses
• Discharges
• Tissue specimens

Question 21

Sample handling

Answer 21

• Anaerobic swabs are a MUST!
  o Sterile swab with oxygen scavenging sachet
• Larger tissue ‘chunks’ can maintain anaerobic microenvironments

Question 22

Lab ID

Answer 22

• Smears of affected tissues can be helpful
• Anaerobic culture
• ID of suspect pathogens by PCR
• *antimicrobial susceptibility testing of anaerobes is POORLY standardized

Question 23

Lab ID ‘materials’ needed

Answer 23

• Anaerobic jar
• Gas-pack (O2 scavenging sachet)
• Anaerobic indicator strip (white=anaerobic, blue=aerobic)
• Pre-reduced media (dull colour blood agar plates_

Question 24

Zoonotic/interspecies transmission

Answer 24

• 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

Question 25

Streptobacillus moniliformis: rat-bite fever

Answer 25

• Found in rodents
• 7-10 day incubation period
• People at risk include
  o Those working with animals
  o Homeless people exposed to urban rats

Question 26

7-10 day incubation period of Streptobacillus moniliformis: rat-bite fever

Answer 26

• 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)

Question 27

Macropapular

Answer 27

• Cutaneous eruption of both macules (altered in colour but not raised) and papules (small, solid, conical elevation of skin)

Question 28

Capnocytophaga canimorsus

Answer 28

• Gram-negative rods
• Slow growing and fastidious
• Carboxyphilic (‘capno’)
• Found in mouths of dogs and cats (80+%)
• Also in humans mouths

Question 29

Capnocytophaga canimorsus: infections in people following dog (or cat) bites

Answer 29

• 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)

Question 30

Following phagocytosis: Capnocytophaga canimorsus

Answer 30

• Continues to replicate and kill host cell

Question 31

Capnocytophaga canimorsus: truck driver with a dog that always licked his face

Answer 31

• Previously splenectomized
• Extremely sick: pyrexic, tachypnic, severe abdominal pain

Question 32

Treatment options

Answer 32

• 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)

Question 33

Drugs to avoid/intrinsic resistance: F. necrophorum

Answer 33

• Penicillin susceptible
• Other species often resistant

Question 34

Drugs to avoid/intrinsic resistance: Bacteroides spp.

Answer 34

• Resistant to penicillin and colistin

Question 35

Drugs to avoid/intrinsic resistance: Capnocytophaga

Answer 35

• Avoid sulfonamides and aminoglycosides

Question 36

Control

Answer 36

• Management practices important
  o Dietary management
  o Paddock and pasture management to keep feet dry/clean