Mathematical modeling to predict the fitness cost associated with triclosan tolerance in Salmonella enterica serovars

Triclosan is a broad spectrum biocide that is incorporated in a wide variety of products for food industry, medical applications and domestic use to reduce microbial load and to improve hygiene. Despite the extended use of the biocide, bacterial tolerance to triclosan is still infrequent. Here, we support the hypothesis that the acquisition of a triclosan tolerance-mediating mutation in the target site for triclosan, the gene fabI, is associated with a fitness cost in Salmonella enterica. Growth competition experiments with mutants exhibiting the Gly93-Val mutation in fabI and their wild-type strains revealed overall decreases in the relative proportions of mutants. For all four serovars investigated, the log10 difference values increased linearly over the experimental time of 96 h. Therefore, a linear regression model was used to characterize the changes in log ratios of wild-type strains and mutants over time. The calculated regression coefficients allowed an estimation of the fitness cost of triclosan tolerance in Salmonella mutants in comparison to their wild-type strains.