PHENOTYPIC AND GENOTYPIC CHARACTERIZATION OF VIBRIO-CHOLERAE ISOLATESFROM A RECENT CHOLERA OUTBREAK IN SENEGAL - COMPARISON WITH ISOLATES FROM GUINEA-BISSAU

A total of 127 strains of Vibrio cholerae (117 V. cholerae O1 and 10 n onagglutinating strains) isolated from a recent cholera outbreak in Se negal and four strains isolated in Guinea-Bissau (during the survey of a cholera epidemic that occurred 10 months before the Senegalese one) were analyzed. Strains were characterized by conventional methods (bi ochemical and serologic identification, susceptibility to antimicrobia l agents), polymerase chain reaction for genes encoding cholera toxin (CtxA), zonula occludens toxin (Zot), and accessory cholera enterotoxi n (Ace), and by ribotyping. Conventional methods showed that all strai ns of V. cholerae O1 belonged to serotype Ogawa, biotype El Tor and we re resistant to the vibriostatic agent O129 (2,4-diamino 6,7-diisoprop ylpteridine phosphate), cotrimoxazole, and chloramphenicol; all strain s were sensitive to tetracycline, a drug that has been extensively use d in cholera therapy. Most of these V. cholerae O1 (112 strains from S enegal and four strains from Guinea-Bissau) had an intact core region (virulence cassette) and amplified a 564-basepair (bp) fragment of ctx A, a 1083-bp fragment of tot, and a 314-bp fragment of ace. Ribotyping of V. cholerae O1 strains after Bgl I restriction of total DNA reveal ed that ribotype B5a, which is the predominant ribotype of this sevent h pandemic of cholera, was not isolated. Instead, a new ribotype was i dentified and designated B27 in our data bank. Since O1 isolates from Guinea-Bissau and Senegal have the same biotype, serotype, and ribotyp e and as the Guinea-Bissau outbreak that preceded the one in Senegal, this emerging ribotype probably came from Guinea-Bissau. Nonagglutinat ing strains exhibited no resistance to the O129 agent and to the teste d antibiotics, they were all negative for virulence cassette, except f or one strain with the ctxA and tot genes isolated from a patient with diarrhea, and there was a great variability of ribotypes among these strains. There was no difference between environmental O1 strains isol ated from water and strains isolated from patients with cholera, sugge sting that fecally contaminated water is an important reservoir for in fection.