TRACKING OF CLINICAL AND ENVIRONMENTAL VIBRIO-CHOLERAE O1 STRAINS BY COMBINED ANALYSIS OF THE PRESENCE OF THE TOXIN CASSETTE, PLASMID CONTENT AND ERIC PCR

Clinical and environmental Vibrio cholerae O1 strains associated with the cholera epidemic in the Luanda province of Angola from 1991 to 199 4 were tracked by toxin distribution, plasmid content and chromosomal polymorphism of the enterobacterial repetitive intergenic consensus (E RIC) sequences by PCR fingerprinting. To follow the distribution of ac e, zot and ctxA toxin genes, 6 specific PCR tests were applied to 100 Vibrio strains, after preliminary hybridization experiments. Clinical isolates of Vibrio cholerae O1 were characterized by high stability of the toxigenic cassette and the presence of a large conjugative multi- resistant plasmid of incompatibility class C. Such characteristics wer e present in all isolates during the four years of the epidemic. Envir onmental strains, isolated from the river supplying water to the Luand a population showed three different genetic profiles. the presence of both cassette and plasmid, the presence of cassette only or absence of both. To assess the clonal relationship between the clinical isolates and the three groups of environmental strains, the strains were analy zed by PCR ERIC polymorphism. This analysis, supported by the toxin an d the plasmid content, suggested the stability of the epidemic strain in clinical cases during the epidemic and led to the finding that ther e was a strict genetic relationship of the epidemic strain with the en vironmental ones as characterized by the presence of the toxin cassett e. The role of the water supply from Bengo River as a reservoir of the Vibrio epidemic strain is discussed.