Anaerobic Spore-forming Bacilli. C. Perferingens And Related Organisms

Question 1

Classification

Answer 1

Family: bacillaceae

These are obligate anaerobic species:

C.perfringens: gas gangrene
C.difficile: acute colitis
C.tetani: tetanus
C.botulinum: food poisoning

Classification of clostridia can be made on the basis of 3 simple criteria:

1) Location and shape of spores
2) pathogenicity to human beings
3) biochemical reactions

Question 2

C. Difficile

Morphology

Answer 2

Gram positive rods

Spore forming

Question 3

Growth characteristics

Answer 3

Obligate anaerobic
Fastidious
Motile

Question 4

Antigenic structure

Answer 4

Surface proteins:

• cell wall protein
• flagella H antigen

Question 5

Virulence factors

Answer 5

Exotoxins:

Toxin A (enterotoxin causing watery diarrhoea)

Toxin B (cytotoxin- kills cells)

Question 6

Disease

Answer 6

C.difficile is normally present in the colon

Causes nosocomial infections - antibiotic associated diarrhea (as antibiotics suppress the normal flora of colon)

Diseases:
> pseudomembranous colitis
> antibiotic-associated diarrhoea (less severe)

Question 7

Microbiological diagnosis

Answer 7

• enterotoxin in the stool is typically detected by using known antibody to the toxin in an ELISA test, or by PCR assay
• enterotoxin in stool can also be detected by cytopathic effect on cell cultures

Question 8

Treatment and prevention

Answer 8

• For pseudomembranous colitis:
  Metronidazole

Oral vancomycin, although effective, should not be used because it may select for vancomycin-resistant enterococi

• For antibiotic- associated diarrhea:
  Discontinuance of the predisposing drug
  Fluid replacement

Prevention: no vaccine