Pathogenic Vibrio Species that Causes Diarrheal Diseases

Let us First examine the antimicrobial sensitivity of pathogenic vibrio species that causes diarrheal diseases. The essential treatment of cholera is fluid and electrolyte replacement. Occasionally, short-course antibiotic therapy e.g. with tetracycline (but resistance is common) or deoxycycline may be indicated to reduce the duration of infection and volume of fluid excreted in those severely dehydrated. Vibrio cholerae El Tor is becoming increasingly resistant to some antimicrobials. Most Vibrio cholerae 0139 strains are susceptible to tetracycline. New oral vaccines against Vibrio cholerae El Tor and Vibrio cholerae 0139 are under development and currently being field tested.

Other Pathogenic Vibrio Species

The following are some of the other vibrios which occasionally cause disease. Depending on species, they can be found in sewage, surface waters, marshes, river estuaries, brackish water, and warm coastal waters. Shellfish and other seafoods can become contaminated.

• Vibrio minicus: Is associated mainly with enteritis following an ingestion of contaminated shellfish, and ear infections following swimming infected water.

• Vibrio fluvalis: Reported as causing gastroenteritis and cholera-like diarrhoeal disease in India, Bangladesh, the Middle East, Egypt, Tunisia, East Africa, Indonesia and the Philippines.

• Vibrio parahaemolyticus: Lives in seawater and estuaries. Ingestion of contaminated raw fish and shellfish can cause severe acute gastroenteritis. Vibrio parahaemolyticus food poisoning has been reported from the Far East, Southeast Asia, Pacific islands and parts of Central America.

• Vibrio alginolyticus: Mainly an opportunistic pathogen causing wounds, ear, and eye infections (it is not enteropathogen).

• Vibrio vulnificus: When ingested, this organism can cause a fatal speticaemia, mainly in patients with liver disease or malignancy. Vibrio vulnifucus is also associated with infections of wounds usually following injuries at sea or when handling infected marine animals. Wounds may become severely inflamed with necrosis of skin and muscle.

• Specimens: include faeces for the isolation of vibrios that cause enteritis, and pus and wound swabs for the isolation of Vibrio alginolyticus and Vibrio vulnificus.

Tests Used to Differentiate Vibrio Organisms that Grow on TCBS Agar

• Sucrose fermentation: V. cholerae, V. fluvialis and V. alginolyticus (not an enteropathogen) produce yellow sucrose-fermentating colonies on TCBS agar. V. mimicus, V. vulnificus and V. parahaemolytic produce green-blue non sucrose fermenting colonies.

• Growth in sodium chloride free peptone water (need not be alkaline) and peptone water containing 80 g/l (8%) and 100 g/l (10%) sodium chloride: Vibrios that are capable of growth at high salt concentrations, e.g. Vibrio alginolyticus and Vibrio parahaemolytic are referred to as halophiles.

• Fermentation of L-arabinose: This test helps to differentiate V. cholerae which does not ferment L-arabinose from V. fluvialis which is L-arabinose fermenting (both species produce yellow colonies on TCBS).

The reactions of the different Vibrios species are summarized in the following table. The reactions of Aeromonas hydrophila are also included as this pathogen, although only occasionally isolated, grows on TCBS agar and requires differentiation from Vibrio cholerae