HALOPHILIC VIBRIO

Those species of Vibrio that require 7-10% sodium chloride for growth are termed halophilic (salt-loving) vibrio. Halophilic vibrios, however grow best in media with 3% NaCl. These vibrios are found in seawater, sewage, prawns and on other seafoods. Important species of halophilic vibrios include V.parahemolyticus, V.fluvialis, V.vulnificus and V.alginolyticus.

Differentiation of halophilic vibrio from non-halophilic vibrios: 
1. Growth on Cystine Lactose Electrolyte Deficient (CLED) medium (pH 7.5): Non-halophilic vibrios grow on this medium but halophilic vibrios don’t. 
2. Growth in peptone water with different concentrations of NaCl. Loopful of bacterial suspension is inoculated into a series of peptone water with NaCl concentration of 0%, 0.5%, 3%, 6%, 8% and 10%. Halophilic vibrios don’t. grow at 0% NaCl concentration, but show increasing growth from 0.5% to 3% or more. Non-halophilic vibrios don’t. grow in NaCl concentration at or beyond 6%.

Vibrio parahemolyticus: It was first isolated from outbreak of gastroenteritis in Japan. In morphology and staining it resembles V.cholerae and is actively motile in liquid cultures. Some degree of pleomorphism is exhibited on culture. On TCBS agar, it grows with green colored colonies due to absence of sucrose fermentation. It grows well in peptone water with 8% NaCl but not at 10%. On MacConkey’s agar it produces non-lactose fermenting colonies. Strains isolated from clinical specimens produce beta hemolysis on Wagatsuma Blood Agar (human blood) while strains isolated from environment don’t. This is known as Kanagawa phenomenon. Infections are associated with consumption of crabs, prawns, shrimps and other seafoods. The clinical infection is characterized by a sudden onset of acute gastroenteritis after an incubation period of 10-20 hours. Infection may also result in diarrhoea, abdominal pain, vomiting and fever. The disease is usually self-limiting as it lasts only for few days. Contamination of an eye injury with pond water has resulted in a case of panophthalmitis. 

Vibrio fluvialis: It was previously called group F vibrio. It grows well on TCBS agar producing yellow colonies. It ferments glucose, lactose, sucrose and arabinose with production of acid but no gas. It is oxidase positive, indole negative and VP negative. It is known to produce cytotoxin and enterotoxin. It has been associated with outbreaks of enteritis.

Vibrio vulnificus: Phenotypically it resembles V.parahemolyticus. It has a polysaccharide capsule. It grows on TCBS medium producing green colonies. It ferments lactose. It is associated with septicemia following wound infections after exposure to seawater or injury in handling crabs. Other infections include fascitis, myonecrosis of the extremities, hepatitis and septicemia. 

Vibrio alginolyticus: It resembles V.parahemolyticus but is sucrose fermenting and VP positive. It is associated with wound infections and ear infection following bathing in sea. It has been isolated from cases of conjunctivitis and bacteremia.