Najran University College of Medicine

1. Najran UniversityCollege of Medicine Enterobacteriaecae 2 BY Dr. Ahmed MoradAsaad Professor of Microbiology

2. Vibrios • Gram (-ve) curved bacilli motile with a single polar flagellum aerobic grow in alkaline pH • Biochemical reactions: • Ferment glucose, maltose, mannite and sucrose with acid only • Indole (+ve) and reduce nitrate • On nitrate-peptone media: nitros-indole is produced giving a red color with strong acids (cholera red reaction) • On TCBS media: pale yellow colonies • Antigenic structure of V. cholerae: • According to the O Ag there are 6 groups: • 1- Group O type-1 (classic and El-Tor biotypes): differentiated by B.R. • 2- Other 5 groups (2 to 6) named non O-1 or non-agglutinablevibrios (NAG) • Group O type-1: Classical Cholera • NAG: Cholera-like disease • H Ag is shared by all groups

3. Cholera • Infectious disease with sever vomiting and watery diarrhea (rice water stool) – rapid dehydration – collapse and shock • Endemic – epidemic - pandemic • Pathogenesis: • Highly infectious disease • By oral route • Water-borne epidemic • Incubation period is 2-5 days • Source of infection: case or carrier • Not invasive disease • Localized to intestine • Heat labile enterotoxin (choleragen) • By V. cholera O-1 • 2 subunits A and B • Subunit B for cell binding promoting entry of subunit A

4. Subunit A: stimulate adenylatecyclase enzyme (stimulate water and electrolytes hypersecretions into lumen) • Laboratory diagnosis • Diagnosis of suspected (first) case in a non-endemic area: • Full identification of the organism is essential before reporting a case of cholera • Stool: rice water stool • Culture on alkaline peptone water for 6-8 hours (surface pellicle) • Subculture on TCBS • Biochemical identification • Serological identification of V. cholera O-1 type • Diagnosis of a case during an epidemic (secondary case): • Direct microscopic examination (Hanging drop) for detecting motile vibrios

5. Diagnosis of a carrier: • Rectal swab • Full identification (important in endemic areas) • Treatment: • I.V. fluids (correct dehydration) • Tetracycline (secondary line) • Prophylaxis: • Community and personal hygiene • Chemoprophylaxis by tetracycline to exposed persons • Vaccination by Koll’s vaccine: • Heat killed vaccine – 2 S.C. injection – limited role (why) • Oral cholera vaccine by DNA recombinent technique

6. Helicobacter pylori • Gram (-ve) spiral-shaped (helical) bacilli, microaerophilic, urease (+ve) • Normal inhabitant of stomach (by ingestion) • Can cause gastritis, peptic ulcer and risk factor for gastric carcinoma • Laboratory diagnosis: • Biopsy of gastric mucosa: Gram stained film • Culture on Skirrow’s medium • Urease breath test: radiolabelled urea is ingested. If the organism is present radiolabelled CO2 is evolved and detected in breath • The presence of IgG Abs in patient’s serum • Detection of H. pylori Ag in stool • Treatment: • Combined therapy with metronidazole, amoxicillin or tetracycline and bismuth salts

7. Cambylobacter • Have long been known as animal pathogens • C. jejuni and C. coli: enterocolitiis (in children) • Morphology: • Gram (-ve) curved or S-shaped bacilli • Motile (cork-screw motility) • Microaerophilic • Growth on Skirrow’s medium at 42⁰ C • Treatment: • Erythromycin and nalidixic acid