Diagnostic microbiology lecture: 6

VIBRIO

Abed ElKader Elottol MSc. Microbiology 2010

SPECIES:

1.Vibrio cholera O1 ( The main species of medical

importance)

2. Vibrio mimicus (Very similar to V. cholera) 3. Vibrio parahemolyticus 4. V. vulnificus

General Characteristics

:

The genus Vibrio is composed of morphologically related species characterized by: a 1. Small gram negative curved rods 2. Motile by polar flagella 3. Aerobic and facultative anaerobes

PATHOGENICITY:

• • • • • •

V. cholera adheres to the walls of the intestine without invading it.

The organism produces a powerful enterotoxin (Exotoxin) that activate the enzyme adenylcyclase.

This leads to the secretion of large volumes of fluids and electrolytes into the leumen of the intestine.

Watery diarrhea is produced.

Rice water stool containing vibrios, epithelial cells and mucous are passed.

In acute choleral cases, the rapid loss of fluids and electrolytes leads to muscular cramps and severe dehydration which if not treated may be fatal.

This Organisms

• Best growth in alkaline conditions (pH 8-9.5) • Alkaline peptone water (pH8.6) - rapid isolation from feces • Selective medium : TCBS • Oxidase positive • Gram-negative curved rods • Single flagellum at one end (actively motile) • Carbole fuchsin is recommended as a counter stain in the gram staining technique when staining vibrio species.

SPECIMEN & MEDIA:

• • • • • =Stool or fecal swab = Media A: Enrichment = Alkaline peptone water (pH 8.6) B: Selective = TCBS : Thiosulfate Citrate Bile Salt Sucrose Agar = In alkaline peptone water: Growth occur within within 4-6 hours.

= In TCBS: Yellow colonies are produced as a results of sucrose fermentation.

PRESUMPTIVE IDENTIFICATION OF VIBRIO

CHOLERA

1. Isolation of sucrose fermenting colonies (yellow) colonies on TCBS.

2. Motility positive and gram negative rods 3. Positive oxidase test

• • • •

4. Positive string test:

A typical yellow colony is rubbed to a microscopic slide, and 2 drops of 0.5 sodium dexoycholate are added.

Try to make uniform suspension.

Negative result is indicated by the formation of a uniform suspension that persist more than one minute.

If the organism lyse so that little or any turbidity develops and the fluid becomes mucoid, such that a "string" is seen when the loop is slowly raised, the test is considered positive.

BIOTYPE OF VIBRIO CHOLERA

• • • • • • Most outbreaks of cholera are now caused by V. cholera

biovar Eltor.

In Bangladesh, however, cholera outbreaks due to Classical biovar.

The following tests can be used to distinguish the 2 biovars: 1. Voges-Proskauer test 2. Haemagglutination of chicken or sheep cells 3. Polymyxin B sensitivity test.

Serological Tests:

• • • • Vibrio species posses O and H antigens.

Vibrio cholera is now divided into 84serovars.

Serovar O1 contains those strains that causes cholera and are agglutinated by V. cholera O group polyvalent antiserum. There are subtypes of O1 group, they are differentiated based on the basis of specific antigenic structures.

Treatment & Antibiotic Sensitivity:

The essential treatment of cholera consist of: 1. Fluid and electrolytes replacement • • • 2. Antibiotic therapy to irradiate the organism .

Tetracycline is the drug of choice for the treatment of V.

cholera infections.

However, in recent years, tetracycline-resistant variants have emerged. For this, sensitivity tests must be performed on all clinical isolates.

Among the known effective antibiotics; tetracycline group, sulfonamides, ampicillin, kanamycin, streptomycin and trimethoprim.

PREVENTION OF CHOLERA

•

Good sanitation & personal hygiene • Immunization with live-attenuated vaccine - stimulates local IgA production • Chemoprophylaxis with tetracycline to close contacts • Prompt detection & treatment of carriers