Characterisation of Triclosan Resistance in Salmonella Enterica Serovar Typhimurium.

Recently the potential for biocide exposure to promote cross resistance to antibiotics has been identified. Triclosan is a broad spectrum antimicrobial incorporated in a wide array of domestic products which acts as an inhibitor of fatty acid biosynthesis by binding to FabI an enoyl-acyl carrier protein. S. Typhimurium is a major cause of human disease and was responsible for over 12,500 cases of enteritis in the U.K in 2004. <P>
I have selected triclosan resistant salmonella from a panel of strains including wild-type strains, DT104 isolates, cyclohexane tolerant strains, gyrA mutants and MAR strains. Analysis of these mutants revealed three distinct phenotypes: low level (MIC of triclosan less than 4mg/L), intermediate level (MIC of triclosan 8-32mg/L) and high-level mutants (MIC of triclosan greater than 32mg/L). Sequencing of fabI revealed a substitution of glycine with valine at position 93 of FabI in various mutants. However this substitution did not correlate with susceptibility to triclosan.<P> I propose to investigate the underlying genetic mechanism(s) of each distinct triclosan resistance phenotype by studying exemplars of each phenotype. The role of FabI in resistance will be defined by complementation of mutants with a FabI G93V substitution and by artificially introducing this substitution into a wild- type strain. Mutants will be studied by microarray analysis and any differences in gene expression between the three phenotypes identified. The contribution of active efflux to each resistance phenotype will be defined and the ability of each class of mutants to develop antibiotic resistance in the presence and absence of efflux pump inhibitors determined. <P>Genomic libraries derived from each class of resistant mutant will be generated and expressed in E. coli, triclosan resistant colonies will be identified and the effector gene(s) characterized. The prevalence of triclosan resistance in a large panel of animal and human isolates of salmonella enterica will be determined.