SummaryThe ability of an isogenic set of mutants of Salmonella enterica serovar Typhimurium L354 (SL1344) with defined deletions in genes encoding components of tripartite efflux pumps, including acrB , acrD , acrF and tolC , to colonize chickens was determined in competition with L354. In addition, the ability of L354 and each mutant to adhere to, and invade, human embryonic intestine cells and mouse monocyte macrophages was determined in vitro . The tolC and acrB knockout mutants were hyper-susceptible to a range of antibiotics, dyes and detergents; the tolC mutant was also more susceptible to acid pH and bile and grew more slowly than L354. Complementation of either gene ablated the phenotype. The tolC mutant poorly adhered to both cell types in vitro and was unable to invade macrophages. The acrB mutant adhered, but did not invade macrophages . In vivo , both the acrB mutant and the tolC mutant colonized poorly and did not persist in the avian gut, whereas the acrD and acrF mutant colonized and persisted as well as L354. These data indicate that the AcrAB-TolC system is important for the colonization of chickens by S . Typhimurium and that this system has a role in mediating adherence and uptake into target host cells.

These data show that triclosan resistance can occur via distinct pathways in salmonella and that mutants selected after single exposure to triclosan are fit enough to compete with wild-type strains.

These data renew fears that the use of biocides may lead to an increased selective pressure towards antibiotic resistance.

Data presented demonstrate that efflux pumps are required for intrinsic resistance to some disinfectants and that exposure to disinfectants can induce expression of the AcrAB-TolC efflux system, but that single exposure was insufficient to select for MAR strains.

These data indicate that multiple antibiotic resistant (MAR)-like Campylobacter strains occur and it may be postulated that these may overexpress cmeABC or another efflux system.