dPBL MMIC:cheng hong (enterocolitis)

Name: Kuan Siew Yan / 29yrs/ Female

Symptom(s):Diarrhoea
Diagnosis: Enterocolitis


What is Enterocolitis?
Cause by organisms that invade the epithelial and the subepithelial tissue of the small and large intestine thus causing inflammation and diarrhea.

Possible Causative Agents
1.Salmonella species
2.Shigella species
3.Campylobacter jejuni
4.Escherichia coli O157

1. Salmonella
§ Characteristics: Rigid, thick walled cell, Gram negative, Facultative straight rods

§ Species: S.typhi, Salmonella choleraeuis, Salmonella enteritidis


§ Pathogenesis: Manifest as Enterocolitis (penetrates through mucosal cells into the lamina propria; need at least 100000 organisms to cause infection). Typhoid/enteric fevers or Septicemia.

§ Biochemical features: Non lactose fermenting colonies on MacConkey/ EMB agar
: Alkaline slant/ acidic butt, gas and H2S in butt in TSI
: Lysine, Aginine, Ornithine positive
: indole neg, methyl red pos, Voges-Proskauer neg, citrate neg


2. Shigella species
§ Charateristics: Rigid, thick walled cell, Gram negative, Facultative straight rods, non-motile

Species: 4 different genus groups (A,B,C,D)


Pathogenesis: virulent (only need 100 organism to cause the disease), transmitted through fecal-oral route, normally have bloody diarrhea

Biochemical features: non-lactose fermenting, no gas production from fermenting glucose, no H2S production, alkaline slant and acidic butt on TSI, indole neg, methyl red pos, vogues proskauer neg, citrate neg, lysine arginine ornithine neg

Other features: a methylene blue stain will differentiate if it is an invasive or toxin producing bacteria (neutrophils will show that it is an invasive infection; like Shigella, Salmonella, Campylobacter


3. Campylobacter jejuni
§ Characteristics: Rigid, thick walled cell, Gram negative, Facultative curved rods (S shape)

§ Species: C. jejuni, C. intestinalis


§ Pathogenesis: Transmitted through fecal oral route or food/water contaminated with Campylobacter, causes entrocolitis

§ Biochemical features: culture on blood plate containing antibiotics (vancomycin, trimethoprim, cephalothin, polymyxin, amphotericin B) and incubate at 42oC at 5%oxygen and 10% carbon dioxide, no H2S production on TSI, hippurate hydrolysis test pos for C. jejuni, susceptible to nalidixic


§ Others: hanging drop shows motility of Campylobacter


4. Escherichia coli O157
Characteristics: Rigid, thick walled cell, Gram negative, Facultative straight rods

Pathogenesis: Enterohemorrhagic infection due to ingesting undercookedmeat, the organism cause the disease by using its features (pili, capsule, endotoxin, 3 exotoxins)-results in watery/ bloody diarrhea


Biochemical features: Can be either lactose fermenting/ non lactose fermenting, appears green on EBM agar, produces indole from tryptophan, decarboxylates lysine, motile, O157:H7 does not ferment sorbitol, acidic slant acidic butt produces gas abd no H2S production

References from:Review of Medical Microbiology and Immunology(9th edition). WARREN LEVINSON

:Color Atlas of Medical Bacteriology. ASM PRESS

Cheng Hong