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Bacillus

Bacillus. Laboratory Diagnosis. Specimen Fluid or pus from local lesion, blood, sputum Microscopy Culture In septicemic anthrax, blood culture should be done Serological test Animal inoculation. Microscopy. Large aerobic, non motile, Gm+ve bacilli

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Bacillus

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  1. Bacillus

  2. Laboratory Diagnosis • Specimen Fluid or pus from local lesion, blood, sputum • Microscopy • Culture In septicemic anthrax, blood culture should be done • Serological test • Animal inoculation

  3. Microscopy • Large aerobic, non motile, Gm+ve bacilli • Arranged singly, in pairs or in short chains, the entire chain is surrounded by a capsule • Capsules are produced in the presence of bicarbonates or 10-25% CO2 • Spores are oval and centrally located, non bulging • Spores are stained by special stains – Sudan black B.

  4. Microscopic features Staining blood films with polychrome methylene blue: - Pink amorphous material around blue bacillus (M’ Fadyean’sreaction): represents capsular material used for the presumptive diagnosis of anthrax in animals.

  5. Cultural Characteristics • Grow on blood or nutrient agar, at 37°C • Irregular, round, raised, dull, opaque, greyish white colonies with a frosted glass appearance. • Low power – edge of the colony is composed of long, interlacing chains of bacilli, resembling locks of matted hair – “Medusa Head Appearance” • Gelatin stab culture – “inverted fir tree” appearance, with slow liquefaction starting from top.

  6. Inverted fir tree • Medusa Head Appearance • wavy colonies with small projections

  7. Cultural Characteristics • “String of Pearls reaction” – • solid medium containing 0.05-0.5 units of Pn/ ml, in 3-6 hrs the cells become large, spherical and occur in chains on agar surface, resembling a string of pearls. differentiates B. anthracis from B. cereus • Selective medium – PLET medium

  8. Smear from colony Morphology in stained smears from cultures • “Bamboo stick appearance” : bacilli arranged end to end in long chains.

  9. Laboratory Diagnosis • Animal inoculation By rubbing contaminated tissues over shaven skin of a guinea pig • Serology • Ascoli’s thermoprecipitation test –to demonstrate anthrax Ag in tissue extracts • EIA(using purified anthrax toxin Ag) • PCRto detect anthrax contamination of animal & agricultural products

  10. Resistance • Bacilli destroyed at 60°C in 30 mins. • Animal carcasses – bacilli remain viable in BM for a wk & in skin for 2 wks. • Spores – highly resistant, survive in soil for 60 yrs • Spores can be destroyed by • 4% KMnO4 in 15 mins • ‘Duckering’ – using formaldehyde solution for animal products imported into non endemic countries

  11. Duckering • For disinfection of wool – 2% soln of formaldehyde at 30- 40°C for 20 mins • Animal hair & bristles – 0.25% at 60°C for 6 hrs

  12. Prophylaxis • General methods of prevention • Improvement of factory hygiene • Proper sterilisation of animal products • Animal carcasses to be buried deep in quicklime or cremated

  13. Prophylaxis • Active immunisation of • Domestic animals with live attenuated spore vaccines • Persons with occupational risk (butchers, farmers, veterinarians) with a cell- free vaccine containing purified protective antigen as immunogen. 3 doses IM with annual booster injections. * Anthrax infection in humans give life long permanent immunity & secondary infections are very rare.

  14. Anthrax vaccines • Original anthrax vaccine – developed by Pasteur – live attenuated bacilli vaccine – strain rendered avirulent by the loss of plasmids which encodes anthrax toxin • Live attenuated anthrax spore vaccine • Sterne vaccine – contains spores of a noncapsulated avirulent mutant strain - loss of plasmid which controls capsule production • Mazucchi vaccine – containsspores of stable attenuated Carbazoo strain

  15. Bacillus cereus • Readily isolated from soil, vegetables and a wide variety of foods including milk, cereals, spices, poultry & meat. • Causes foodborne gastroenteritis – 2 patterns of disease (diarrhoeal & emetic); both types are mild & self limited, requiring no specific therapy.

  16. Bacillus cereus clinical presentation Gastroenteritis DIARRHOEALFORM EMETIC FORM Incubation period > 6 hours Diarrhoea Lasts 20-36 hours Incubation period < 6 hours Severe vomiting Lasts 8-10 hours

  17. Type I Wide range of foods including cooked meat & vegetables Diarrhoea & abdominal pain develops 8 –16 hrs after consumption Few bacilli seen in fecal specimens Caused by serotypes 2,6,8,9,10 or 12. Enterotoxin resembles LT of E.coli Type II Chinese fried rice exclusively. Acute nausea & vomiting 1-5 hrs after meals, diarrhoea rare Large no of bacilli in cooked rice & fecal samples. Caused by serotypes 1,3 or 5 Toxin resembles staphylococcal enterotoxin Types of Gastroenteritis

  18. Diagnosis • Primarily depends on clinical diagnosis & food sources • Laboratory Diagnosis • Specimen – stool, vomitus, food, blood • Microscopy – not of much help • Culture • Test for toxin – to differentiate from staphylococcal food poisoning.

  19. Culture • Blood agar • Special MYPA medium: Mannitol - egg yolk - phenol red – polymyxin agar : to isolate B.cereus from feces & other sources.

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