Lec. No. 8 Dr. Manahil Diagnostic laboratory tests Microscopic examination: Gram stained smear
The appearance of large encapsulated gram positive bacilli in the blood is strongly presumptive for Bacillus anthracis identification. Anthrax can be identified in dried smears by immunofluorescent staining technique. Macfadyean's reaction for demonstration of capsule by using polychrome methylene blue stain to stain blood film.
Cultural characteristics: Colonies on sheep blood agar. Phenyl ethyl alcohol (PEA) media used for stools suspected of containing Bacillus anthracis. Non-motile organism. Serological tests Ascoli's test. ELISA test Demonstrating antibodies in patient serum. PCR Used for rapid testing of potentially contaminated animal products.
Treatment B. anthracis is susceptible to penicillin which considered the treatment of choice for a suspected infection. The organisms are susceptible to deoxycycline and ciprofloxacin, and they used also for chemoprophylaxis in suspected exposure. B. anthracis strains are resistant to sulfonamides and extended spectrum cephalosporins.
Resistance and immunity Anthrax infection in man provides a permanent immunity and second attacks are extremely rare. Active immunity to anthrax can be induced in susceptible animals by vaccination with: spore suspension from attenuated strain produce all three toxin proteins, but lack the capsule In human Vaccine prepared from Culture filtrate of Atoxigenic, non capsulated, a virulent starin
Prevention and control Vaccination of animal herds in endemic regions. Burning or burial of animals that die of anthrax. Decontamination of animal products like hides and wool. Disposal of animal carcasses by burning. Protective clothing and gloves for handling infected materials. Improvement of factory hygiene. Vaccination of people who live in area where the disease is endemic. Person to person transmission is rare.
Saprophytic species The main diseases caused by B. cereus: 1. Food poisoning has two types The emetic and diarrhoeal. - The emetic type associated with fried rice. - The diarrheal type associated with meat dishes and sauces. B. cereus produce two toxins: Enterotoxin cause diarrhoea Emetic toxins cause nausea and vomiting
The emetic form is manifested by nausea, vomiting, abdominal cramps, is self-limiting, with recovery occurring within 24 hours. It begins 1-5 hour after ingestion of rice. The diarrheal form has an incubation period of 1-24 hrs. and is manifested by diarrhea with abdominal pain and cramps. Fever and vomiting are uncommon. The enterotoxin may be performed in the food or produced in the intestine.
2. ocular disease B. cereus is an important cause of eye infection, e.g. keratitis, endopthalimitis. The organisms are introduced into the eye by foreign bodies associated with trauma. 3. Other disease Including wound infections, primary cutaneous infections, urinary tract infection, pneumonia, lung abscess, brain abscess, osteomylitis, bacteremia, seplicemia and others.
Treatment and prevention Vancomycin, clindamycin, ciprofloxacin, and gentamicin can be used to treat infection. Penicillin and cephalosporin are effective (B. cereus produces abroad-spectrum beta lactamase and thus it is resistant to such antibiotics). Rapid consumption of foods after cooking and proper refrigeration of uneaten foods can prevent food poisoning.