A rapid and reliable species-specific identification of clinical and environmental isolates of Vibrio cholerae using a three-test procedure and recA polymerase chain reaction.

Purpose: Vibrio cholerae, the cause of cholera, is one of the leading causes of morbidity and mortality in many developing countries. Most laboratories initially rely on biochemical tests for a presumptive identification of these strains, followed by a polymerase chain reaction (PCR)-based method to confirm their identification. The aim of this study is to establish a rapid and reliable identification scheme for V. cholerae using a minimal, but highly specific number of biochemical tests and a PCR assay. Materials and Methods: We developed a species-specific PCR to identify V. cholerae, using a housekeeping gene recA, and used that to evaluate the sensitivity and specificity of 12 biochemical tests commonly used for screening and / or presumptive identification of V. cholerae in the clinical and environmental samples. Results: Here we introduced a combination of three biochemical tests, namely, sucrose fermentation, oxidase test, and growth in trypton broth containing 0% NaCl, as also the PCR of the recA gene, for rapid identification of V. cholerae isolates, with 100% sensitivity and specificity. The established method accurately identified a collection of 47 V. cholerae strains isolated from the clinical cases (n = 26) and surface waters (n = 21), while none of the 32 control strains belonging to different species were positive in this assay. Conclusion: The triple-test procedure introduced here is a simple and useful assay which can be adopted in cholera surveillance programs for efficient monitoring of V. cholerae in surface water and fecal samples.

Occurrence of colonization factor antigens I & II in enterotoxigenic Escherichia coli associated diarrhoea in Iran & correlation with severity of disease.

The occurrence of colonization factor antigens I and II (CFA/I and II) and type 1 somatic pili was investigated in 197 enterotoxigenic Esch. coli (ETEC) isolated from 197 patients of diarrhoea (aged under 3 yr) during February 1985 to March 1986 in Tehran, Iran. Among ETEC strains, 154 strains were heat-stable enterotoxin (ST) producers, 27 strains were heat-labile enterotoxin (LT) producers, and 16 strains produced both toxins. Sixty five (33%) strains showed mannose-resistant haemagglutination (MRHA) of human and/or bovine erythrocytes; of these, 51 (86%) strains were positive for CFA/I and II. Seventy one (36%) strains also exhibited type 1 somatic pili. CFA/I was found in 4 (15%) LT producing, 24 (16%) ST producing, and 2 (13%) LT/ST producing strains. In contrast, CFA/II was only found in ST producing strains (17 strains) and those producing both toxins (4 strains). Patients having CFAs-positive ETEC strains had a significantly (P less than 0.001) higher number of stool evacuation per day and a longer duration of diarrhoea than those having CFAs-negative strains. Fifty nine patients had mixed infections of ETEC strains and other enteropathogens. CFA/I or II (CFAs)-positive and CFAs-negative ETEC strains were found in 17 and 42 patients with mixed infections respectively. The mean number of stool evacuations per day was much higher in patients with ETEC and rotavirus than those with only ETEC infection (P less than 0.001). However, severity of the disease was not affected by the presence or absence of CFA/I or II in ETEC strains found in these patients.