Simple serological tests for detecting classical heat labile enterotoxin (LT-I) of Escherichia coli

Diarrhoea caused by enterotoxigenic Escherichia coli (ETEC) remains a problem in Southeast Asia. At present, no routine laboratories as yet are available for ETEC detection. In this study, attempts were made to produce reagents for use in simple serological tests for detecting LT. The serological methods were the Biken, the staphylococcal coagglutination and the reverse passive hemagglutination tests. For the Biken test, medium was prepared locally by mixing constituents as described previously by Honda et al., (1981). Anti-CT-B subunit was prepared by immunizing a rabbit with commercial CT-B subunits (Sigma). Other chemical reagents e.g. colistin, lincomycin etc. were obtained from the local supplies. Using the locally made reagents to detect LT from 100 WHO reference strains of E. coli by the Biken test, it was found that the test had 100%, 92%, 96%, 100% and 92.5% of specificity, sensitivity, accuracy, positive predictive value and negative predictive value, respectively. Protein A rich Staphylococcus aureus from the stock culture of the Department of Microbiology and Immunology, Faculty of Tropical Medicine, Mahidol University were grown in suitable medium i.e. blood agar containing lincomycin (BA-Lin). Suitable amount of the rabbit anti CT-B subunit (0.1 ml) was used to sensitize each ml of the formalinized, heat-fixed bacteria. The sensitized bacteria were used for detecting LT in the lysates of the 100 E. coli reference strains. The lysates were prepared by growing the E. coli strains on BA-Lin medium for 8 hours, then a loopful of each strain was inoculated into colistin solution (20,000 unit/ml).(ABSTRACT TRUNCATED AT 250 WORDS)