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Abstract
BackgroundOver the last decade, cholera outbreaks in parts of Kenya have become common. Although a number of recent studies describe the epidemiology of cholera in Kenya, there is paucity of information concerning the diversity and occurrence of mobile genetic elements in Vibrio cholerae strains implicated in these outbreaks. A total of 65 Vibrio cholerae O1 El Tor serotype Inaba isolated between 1994 and 2007 from various outbreaks in Kenya were investigated for mobile genetic elements including integrons, transposons, the integrating conjugative elements (ICEs), conjugative plasmids and for their genotypic relatedness.ResultsAll the strains were haemolytic on 5% sheep blood and positive for the Vibrio cholerae El Tor-specific haemolysin toxin gene (hylA) by PCR. They all contained strB, sulII, floR and the dfrA1 genes encoding resistance to streptomycin, sulfamethoxazole, chloramphenicol and trimethoprim respectively. These genes, together with an ICE belonging to the SXT/R391 family were transferable to the rifampicin-resistant E. coli C600 en bloc. All the strains were negative for integron class 1, 2 and 3 and for transposase gene of transposon Tn7 but were positive for integron class 4 and the trpM gene of transposon Tn21. No plasmids were isolated from any of the 65 strains. All the strains were also positive for all V. cholera El Tor pathogenic genes except the NAG- specific heat-stable toxin (st) gene. None of the strains were positive for virulence genes associated with the V. cholerae classical biotype. All the strains were positive for El Tor-specific CTXphi bacteriophage rstrR repressor gene (CTXETΦ) but negative for the Classical, Calcutta, and the Environmental repressor types. Pulse Field Gel Electrophoresis (PFGE) showed that regardless of the year of isolation, all the strains bearing the SXT element were clonally related.ConclusionsThis study demonstrates that the V. cholerae O1 strains carrying an SXT/R391-like element implicated in recent cholera outbreaks in Kenya has not changed significantly between 1994 and 2007 and are clonally related.
Highlights
Over the last decade, cholera outbreaks in parts of Kenya have become common
PCR analysis of the donor strains and the E. coli C600 transconjugants amplified a 626 bp fragment of sulII gene encoding resistance to sulfamethoxazole, a 278 bp amplicon corresponding to the dfrA1 gene encoding resistance to trimethoprim, a 515 bp fragment of strB encoding resistance to streptomycin, a 526 bp fragment of floR gene conferring resistance to chloramphenicol and a 1035 bp fragment corresponding to the integrase gene of the SXT/R391 integrating conjugative elements (ICEs) family, confirming co-transfer of resistance markers and this element
V. cholerae O1 strains resistant to tetracycline have previously been reported in Kenya [6] and Zambia [41] in the 1990s, but those isolated from Ethiopia [42] and Somalia [43] in the same period were susceptible to this antibiotic
Summary
A number of recent studies describe the epidemiology of cholera in Kenya, there is paucity of information concerning the diversity and occurrence of mobile genetic elements in Vibrio cholerae strains implicated in these outbreaks. A total of 65 Vibrio cholerae O1 El Tor serotype Inaba isolated between 1994 and 2007 from various outbreaks in Kenya were investigated for mobile genetic elements including integrons, transposons, the integrating conjugative elements (ICEs), conjugative plasmids and for their genotypic relatedness. From 1974 to 1989, outbreaks were reported every year with an average case fatality rate of 3.6% [1]. More cases have been reported locally since 2005 [4] and the recent outbreak in 2007 had a case fatality of up to 5.6% [1]
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