Najran University
College of Medicine
Enterobacteriaecae 2
BY
Dr. Ahmed Morad Asaad
Professor of Microbiology
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-agglutinable vibrios
(NAG)
Group O type-1: Classical Cholera
NAG: Cholera-like disease
H Ag is shared by all groups
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
Subunit A: stimulate adenylate cyclase 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
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
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
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