Characterization Of Toxigenic Vibrio Cholerae Isolates From Kenya, 2007-2010

ABSTRACT

Over the last decade cholera outbreaks have become common in some parts of Kenya. A number of recent studies have described the epidemiology of cholera in Kenya but there has been little information regarding the phenotypic and molecular characteristics of Vibrio cholerae in these outbreaks. The aim of this study was therefore to characterize Vibrio cholerae isolates from Kenya. A total of 168 Vibrio cholerae O1, biotype El Tor isolates collected between 2007 and 2010 from various cholera outbreaks in Kenya were studied. Their serotypes, antimicrobial susceptibility, genetic mechanisms of resistance, and their genetic relatedness were determined. Biochemical identification was performed using the API 20E identification system. Serologic identification was done by slide agglutination. Antimicrobial susceptibility testing was performed using the E-test method and disk diffusion. Polymerase Chain Reaction (PCR) was used to detect pathogenic and antibiotic resistant genes whereas Pulsed-field Gel Electrophoresis (PFGE) was used to determine their genetic diversity. Biochemical characterization confirmed all isolates as Vibrio cholerae belonging to serotypes Inaba and Ogawa, with Inaba being the predominant one. The isolates displayed reduced susceptibity towards ceftriaxone, chloramphenicol, doxycycline and streptomycin antimicrobials. Majority were resistant to amoxicillin, cotrimoxazole, erythromycin and nalidixic acid. Notably, 45% of the isolates were resistant to three or more of the antimicrobials recommended for cholera treatment. All were susceptible to ciprofloxacin, gentamicin and ofloxacin. Majority of the isolates were also resistant to O/129 Vibriostatic agent that is used to differentiate Vibrio species from closely related organisms. PCR results for detection of virulence genes revealed that the isolates harbored the cholera toxin, ctxA and/or the cholera toxin regulatory gene, toxR. They were found to harbor genetic determinants for antimicrobial resistance namely the SXT integrating conjugative element and the class one intergron. Genes that code for antimicrobial resistance were detected in these elements. Pulsed-field Gel Electrophoresis results suggest that two clones of Vibrio cholerae strains were circulating within Kenya. The finding that a majority of the Kenyan isolates were resistant towards cotrimoxazole and erythromycin suggest that these antimicrobials should not be used to treat cholera caused by current Vibrio cholerae O1 strains. Surveillance for antimicrobial drug resistance should continue among Vibrio cholerae isolates. The finding that most isolates were resistant towards the O/129 Vibriostatic agent suggests that the agent should not be used to characterize Kenyan isolates. Whole genome sequencing should be performed to better understand the genetic mechanisms of resistance and genetic relatedness of these isolates. The findings from this study will be presented to the Kenyan Ministry of Health and hopefully be used in policy making.