Genetic Basis, Transferability And Linkage Of Streptomycin And Sulphonamide Resistance Genes In Escherichia Coli From Food Animals In Kenya

The genetic basis and transferability of streptomycin and sulphonamide resistance was studied in 23 Escherichia coli isolates from food animals in Kenya. Physical linkage of the streptomycin resistance gene strA with sulphonamide resistance gene sul2 was investigated by PCR and confirmed by sequencing. Two small plasmids of 6 kb (pSSGK1) and 8 kb, (pSSTGK1) identified by transformation to mediate resistance to at least streptomycin and sulphonamide were restricted in order to define their relatedness. Their restriction maps were compared to one another and with the maps of other plasmids from E. coli known to mediate these resistance properties. Streptomycin resistance was based on the expression of the strA, strB and/or aadA1 genes, while sulphonamide resistance was encoded by the sul2 or sul1 gene. The strA, strB and sul2 genes were transferable via conjugation and transformation. Physically linked sul2 and strA genes were present in both plasmids pSSGK1 and pSSTGK1. The plasmids pSSGK1 and pSSTGK1 were different from each other, but similar respectively to sulphonamide/streptomycin and sulphonamide/streptomycin/tetracycline resistance plasmids described previously in uropathogenic E. coli from humans. Conjugation of plasmids encoding streptomycin and sulphonamide resistance may be one mechanism for the wide dissemination and persistence of these resistances among food animal E. coli in Kenya. Physical linkage of the plasmid-borne strA and sul2 genes would facilitate the spread of these genes by co-selection during selective pressure imposed by the use either of the two antimicrobials and highlights the need for the prudent use of streptomycin or sulphonamides in animal husbandry. La base genetique et la transferabilite de la resistance a la streptomycine et au sulfamide ont ete etudiees chez 23 souches de Escherichia coli issues d'aliments d'origine animale au Kenya. Le lien physique du gene strA de resistance a la streptomycine avec le gene sul2 de resistance au sulfamide a ete examine par PCR et confirme par sequencage. Deux petits plasmides de 6 kb (pSSGK1) et de 8 kb (pSSTGK1) identifies par transformation pour modifier la resistance au moins a la streptomycine et au sulfamide etaient restreints en vue d'etablir leur lien. Leurs cartes de restriction etaient comparees les unes aux autres ainsi qu'avec les cartes des autres plasmides issus de E. coli pour modifier leurs proprietes de resistance. La resistance a la streptomycine etait fondee sur l'expression des genes strA, strB et/ ou aadA1, alors que la resistance au sulfamide etait codee par le gene sul2 ou sul1. Les genes strA, strB et sul2 etaient transferables par le biais de conjugaison et de transformation. Les genes sul2 et strA physiquement lies etaient presents dans les deux plasmides pSSGK1 et pSSTGK1. Les plasmides pSSGK1 et pSSTGK1 etaient differents l'un de l'autre, mais respectivement semblables aux plasmides de resistance au sulfamide/streptomycine et sulfamide/streptomycine/tetracycline decrits auparavant dans E. coli uropathogenes issus des humains. La conjugaison des plasmides codant la resistance a la streptomycine et au sulfamide peut etre un mecanisme pour la large diffusion et la persistance de ces resistances dans E. coli issus des aliments d'origine animale au Kenya. Le lien physique des genes strA et sul2 transportes par le plasmide pourrait faciliter la propagation de ces genes par une co-selection au cours de la pression selective imposee par l'utilisation de l'un ou l'autre des deux agents antimicrobiens, et souligne la necessite de recourir a l'usage judicieux de la streptomycine ou du sulfamide dans l'elevage. Bulletin of Animal Health and Production in Africa Vol. 56 (1) 2008: pp. 56-66