Molecular characterisation of Vibrio cholerae O1 strains carrying an SXT/R391-like element from cholera outbreaks in Kenya: 1994-2007

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.

Antimicrobial Resistance and Virulence: a Successful or Deleterious Association in the Bacterial World?

“…SXT/ R391 ICEs are directly involved in the transmission of multiple drug resistance in different species, including Vibrio species (248). Indeed, analysis of some isolates from cholera outbreaks has revealed the involvement of SXT/R391-like genes in the transmission of virulence and resistance (248,249). The in vitro plasticity and capacity of the SXT-related ICE from Vibrio cholerae to transfer virulence genes to other species such as E. coli has also been demonstrated (250).…”

The influence of the accessory genome on bacterial pathogen evolution

“…[58][59][60]88,89 Integrons have been found in a wide range of non-pathogenic and pathogenic bacteria in environments ranging from marine to terrestrial organisms and niches. 73,77,83,[90][91][92][93][94][95][96][97][98][99][100][101] Two types of integrons, the chromosomal integron (CI) and mobile integron (MI) have been identified: 70 CIs appear to represent a "core" gene capture system in Gram negative bacteria to enable genome flexibility for adaptation to diverse environments. The five classes of MIs defined so far (based on intI sequence similarity) are associated with MGEs such as transposons and plasmids and thus provide a pool of elements for shuttling genes throughout microbial communities.…”

Genetic Analysis of CTX Prophage and Antibiotic Resistance Determinants in Vibrio cholerae O1 Belonging to the Atypical El Tor Biotype from Kelantan, Malaysia

“…The emergence of multidrug-resistant V. cholerae strains has been documented frequently in recent years (Kiiru et al, 2009;Jain et al, 2011) and this phenomenon has led to repeated calls for the more prudent use of antibiotics by the global community. Multidrug-resistant V. cholerae have been reported from Malaysia and the antibiogram profile of the Kelantan outbreak strain showed that the isolates were resistant to various antibiotics, including, tetracycline, erythromycin, sulfamethoxazole-trimethoprim, streptomycin, penicillin G, and polymyxin B.…”