Bacillus species in medical microbiology

Bacillus species in medical microbiology

1. Bacillus Anthrax; food poisoning

2. Introduction Species B. anthracis B. cereus B. subtilis B. pumilis B. stearothermophilus B. licheniformis B. thuringiensis Aerobic non bulging spore formers Led to development of Koch’s postulates

3. Bacillus anthracis Large gram positive Forms oval, central or sub terminal, non bulging spore Capsulated in tissues Non motile Aerobic Mesophiles - @ 35˚C

4. Virulence factors and Pathogenesis Anthrax- zoonotic disease Man is infected accidentally during contact with infected animals or their products B. anthracis spores introduced into the body are phagocytosed by macrophages Transported from site of infection to regional lymph nodes Germinate and vegetative bacteria multiply enter the bloodstream causing massive septiceamia

5. Cont…. Pathogenicity of B. anthracis depends on: Capsule Toxin complex protective antigen, oedema and lethal factor Pathogenesis of B. anthracis is related to sensitivity of macrophages to: Capsule antiphagocytic Adenylate cyclase activity of oedema factor Metalloprotease activity of lethal factor

6. Clinical features Cutaneous anthrax Commonest form; bacilli enters through damaged skin, produce a malignant pustule, ulcerates and forms an eschar surrounded by vesicles containing serous fluid and an area of oedema

7. Cont…. Enteric anthrax Results from ingestion of infected meat; it’s a severe form of gastroenteritis presenting with fever, abdominal pain, blood diarrhea. Patient dies from septiceamia Inhalation anthrax Inhalation of spores during shaving, sorting or handling of animal hair; the spores lodge in the alveoli of the lungs, germinate and multiply producing pneumonia like symptoms

8. Laboratory Diagnosis Clinical specimen Fluid aspirated from cutaneous lesions, sputum, stool, blood Large Gram positive bacilli Catalase and Vogues Poskauer positive MacFadyean reaction Demonstrate the bacilli in tissues Ascoli test Antigen antibody reaction (suspected carcass)

9. Cont… Culture Blood agar – large, flat, irregular non heamolytic colonies Medusa head (coiled wavy margins and curled edges) on dissecting microscope Gelatin media stab Inverted fir tree Selective media PLET PCR, ELISA

10. Treatment Penicillin, macrolides, aminoglycosides, tetracycline and chloramphenicol Fluoroquinolones – ciprofloxacin; prophylaxis or those considered at risk of exposure Prevention and control

11. Vaccine BioThrax ® people 18 through 65 years old at increased risk of exposure Five doses, with a booster dose each year thereafter for those that continue to be at increased risk of exposure. In combination with antibiotics, as a three-dose primary series after exposure.

12. Other Bacillus species - anthracoides General characteristics Gram positive rods Form spores, centrally positioned Motile with pretrichous flagella Beta heamolytic colonies on BA McFadyean reaction negative Non capsulated

13. Cont….. B. cereus Food poisoning, anthrax like disease, eye infections Tissue destruction is mediated by cytotoxic enzymes, including cereolysin and phospholipase C B. subtilis and B. licheniformis Source of bacitracin ; contaminant of specimens and lab media B. stearothermophilus Biological control in autoclaves B. polymixa Source of polymixin antibiotic