Saturday, 8 December 2007

Cheng Hong: MMic PBL Kuan Siew Yan follow up

There are some other organisms and viruses that are able to cause diarrhea like:

Clostridium perfringens
Staphylococcus aureus
§ Rotavirus
§ Norovirus
§ Vibrio cholerae

Clostridium perfringens
Characteristics: Rigid, thick walled cell, gram positive, spore forming anaerobic rods

Pathogenesis: Causes gas gangrene and food poisoning. C. perfringens is a normal flora in the colon but not found in the small bowels. If it is in the small bowels, the enterotoxin (super antigen on the C. perfringens) will cause diarrhea.

Why is not likely in this case: The diarrhea will only last for 24hrs and the disease will be resolved after 24hrs. This bacteria do not cause enterocolitis.

Staphylococcus aureus
Characteristics: Rigid, thick walled cell, gram positive cocci

Pathogenesis: Causes food poisoning. The enterotoxin causes food poisoning (vomiting/ watery, non-bloody diarrhea). The enterotoxin acts like a super antigen and stimulate the release of interleukin-1 and 2. May be transmitted through improperly cooked food as S. aureus is quite heat resistant.

Biochemical features: Coagulase positive, positive latex test, plate on Mannitol salt agar which acts as a selective medium and differential medium

Others: Smears will show gram positive cocci in clusters (purple).

Characteristics:Reovirus family, non-enveloped, ssRNA virus, Icosahedral capsid

Pathogenesis: Causes diarrhea in young children, transmitted through fecal oral route. The virus multiplies in the small intestine and causing salt, glucose, water to be loss through diarrhea.

Diagnosis: Using ELISA techniques/ radioimmunology/ Rapid testing kits

Why it is not likely in this case: As Rotavirus infection mostly occurs in babies and very young children. Adults rarely will be infected as at the age of 6, children will have antibodies against at least 1 serotype of rotavirus.

Characteristics: Calicivirus family, non-enveloped, ssRNA virus, Icosahedral capsid

Pathogenesis: Transmitted through fecal oral route, or ingesting contaminated seafood/water. Virulent (low infectious dose). May cause vomiting, fever, diarrhea.

Diagnosis: PCR method or ELISA method

Vibrio cholerae
Characteristics: Rigid, thick walled cell, Gram negative, Facultative curved rods (comma shape)

Pathogenesis: Transmitted through fecal contamination in water and food, found in shellfish/ oysters. It causes watery diarrhea by causing the cells in the gut to lose water and ion. It does not cause bloody diarrhea or abdominal pain.

Biochemical features: oxidase positive, acid slant and acid butt, but no gas or H2S on TSI. Can be confirmed usingagglutination test (polyvalent O1 or non-O1 antiserum.

Please click the link below to view the biochemical test. (Maximise the table for better viewing)

References from:Review of Medical Microbiology and Immunology(9th edition). WARREN LEVINSON
:Color Atlas of Medical Bacteriology. ASM PRESS

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