Patient 4-Ng Ming En (Nora)

Patient 4-Ng Ming En
Complaints: Severe vomiting, diarrhea, abdominal cramps
Diagnosis: Food poisoning

Food Poisoning is the result of eating organisms or toxins in contaminated food. Based on the patient’s complaints, the food poisoning can be caused by these microorganisms: Staphylococcus aureus, Vibrio cholerae, and Bacillus cereus.

1. S. aureus
•Normally found in ham, poultry, egg dishes, and pastries.
•S. aureus food poisoning is often caused when a food handler contaminates food products that are served or stored at room temperature. After the staphylococci have been introduced into the food, the food must remain at room temperature or warmer for the organisms to grow and release the toxin. Subsequent heating of the food will kill the bacteria but not inactivate the heat stable toxin.
•There are multiple enterotoxins: A-E, G-I, K-. The enterotoxins are heat stable and resistant to the action of gut enzymes. The enterotoxins is preformed in foods and has a short incubation period (1-8 hours)
•S. aureus food poisoning is characterized by severe vomiting, watery diarrhea, and abdominal pain. The emetic effect of enterotoxins is probably the result of central nervous system stimulation after the toxin acts on the neuron receptors in the guts. The enterotoxins genes will interact with accessory genetic elements (bacteriophages) to produce the toxins.
•Specimens are cultured on BAP at 370C for at least 18 hours. Young cocci stain strongly positive, on aging, many become negative. S. aureus produce catalase and coagulase.
•Susceptibility testing: resistance to Penicillin G can be predicted by a positive test for Beta-lactamase. Resistance to nafcillin and methicillin occurs in about 20%.
S. aureus on BAP (http://www2.umdnj.edu)


2. V. cholerae
•Normally found in shellfish
•When V. cholerae is ingested, it will colonies the small intestine.
•It is a non-invasive and causes disease by producing enterotoxins, called choleragen (heat labile toxin). These toxins can cause watery diarrhea (rice-waster stool). This is because the toxins will result in excess secretion of calcium ions into the intestinal lumen. Water, sodium, potassium and bicarbonate all follow due to concentration and electrical gradients.
•V. cholerae is a gram negative bacilli, and when a smear is done, dark field or phase contrast microscopy may show the rapidly motile Vibrio
•Specimen is to be cultured on TCBS; forms yellow colonies that are readily visible against the dark green background of the agar. For enrichment, a few drops of stool can be incubated for 6-8 hours in taurocholate-peptone broth (pH 8.0-9.0). And this can be used for staining and subculturing. V. cholera is oxidase positive.
•Confirmatory test: further identified by slide agglutination tests using anti-O group 1 antisera.
V. cholerae on TCBS (http://www.chp.gov.hk):




B. cereus
-associated with the consumption of cereals and cooked food (Chinese fried rice syndrome)
•Food poisoning caused by B. cereus has 2 distinct forms: the emetic type and the diarrheal type. The emetic type begins 1-5hours after ingestion of rice. When rice are cooked and allowed to cool slowly, the B. cereus spores germinate and the vegetative cells produce the toxins during log phase growth or during sporulation. The diarrheal form has an incubation period of 1-24 hours. The enterotoxin may be preformed in the food or produced in the intestine.
•Specimen is to be cultured on BAP. Strong Beta-hemolysis and irregular colonies are noted. B. cereus is catalase positive, and can be non-motile or motile.spore-forming, facultatively anaerobic rod.

•B. cereus can also be confirmed using immunological detection (http://www.rci.rutgers.edu)
click on this link: http://i17.tinypic.com/2mowfg6.jpg


Bacillus cereus on BAP (http://en.wikipedia.org)



References:
1. Brooks, G. F., Butel, J. S. & Ornston, L. N.; “Jawetz, Melnick & Adeberg’s Medical Microbiology”
2. Patrick R. Murray, Ken S. Rosenthal, George S. Kobayashi, Micheal A. PFaller.; "Medical Microbiology"
3. Monica Gandhi, Paul Baun, C Bradley Hare, Aaron B Caughey.; "Microbiology and Immunology"

Poated by Nora