Bacillus cereus - Microbial Food Poisoning

MICROBIAL FOOD POISONING

Bacteria

·              Bacterial food poisoning is most frequently caused by Staphylococcus, followed by Clostridium perfringens, Salmonella, Shigella, and Streptococcus in descending orderof frequency.

Bacillus cereus

·              Bacillus cereus is an endemic, soil-dwelling, Gram-positive,rod shaped, beta haemolytic bacterium that is well known to cause foodborne illness. It is a facultative aerobe, and like other members of the genus Bacillus can produce protective endo-spores that are resistant to extremes of temperature. Various strains have been shown to produce seven different toxins.

Source

·      Emetic form: Fried and cooked rice, pasta, pastry, and noodles.

·      Diarrhoeal form: Meat and vegetables.

·      Other potential sources of infection include spices, pasteur-ised fresh or powdered milk, and reconstituted milk-based infant formula.

Toxin

■■   Emetic form: Highly stable toxin, cereulide, which has a ring structure consisting of four amino and/or oxy acids. It is resistant to heat, pH, and proteolysis, but is not consid-ered antigenic.

■■Diarrhoeal form: Heat and acid-labile enterotoxin (a protein), that is sensitive to proteolytic enzymes.

Incubation Period

■■   Emetic form: 1 to 5 hours.

■■   Diarrhoeal form: 8 to 16 hours.

Clinical Features

·              Emetic form: Nausea, vomiting.

·              Diarrhoeal form: Diarrhoea (watery), abdominal pain, and occasionally nausea.

Fever is uncommon in both forms.

In rare cases, fulminant liver failure developed following the consumption of food contaminated with B. cereus emetic toxin. B. cereus endophthalmitis has been reported in a toddler following eye trauma (laceration of the eye with a manure fork). In one retrospective review of surgical patients who developed B. cereus wound infections, most appeared to have serous and haemorrhagic drainage, often profuse, lasting 1 to 3 weeks. Endocarditis has been reported in patients following intravenous drug abuse and valvular heart disease.

Diagnosis (for food-borne illnesses)

Stool culture and growth in MYPA (mannitol, egg yolk, phenol red, polymyxin agar) medium. Diagnosis can be confirmed by detecting the organisms in the suspected food item.

Treatment

·      Supportive measures. The disease is usually mild and self-limiting.

·      Monitor fluid and electrolyte status and hepatic enzymes as indicated.

·      Patients with mild fluid deficits can often be managed with oral fluid therapy consisting of clear liquids, or specially formulated glucose and electrolyte solutions. Patients with moderate to severe dehydration must be treated with IV fluids.

·      Significant nausea and vomiting in adults may be controlled with a suitable antiemetic agent.

·      For wound infections, antibiotic susceptibility testing should be done. Chloramphenicol, tetracycline, kanamycin, gentamicin, clindamycin, vancomycin, and erythromycin are generally effective. Resistance has been reported to penicillin and cephalosporines secondary to beta-lactamase production.