Possible associations between Salmonella persistence in poultry houses and resistance to commonly used disinfectants and a putative role of mar.

A putative link between Salmonella persistence in the agricultural sector and resistance to disinfectants has been sparsely investigated. Therefore, minimum inhibitory concentration (MIC) tests against five disinfectants commonly used in poultry premises (formaldehyde, glutaraldehyde/benzalkonium chloride compound, oxidising compound, tar oil phenol, iodophor) were performed on 286 Salmonella isolates, including 256 from Danish broiler houses, altogether representing nine serotypes. Six of these isolates were used for adaptation and de-adaptation studies involving the five disinfectants. Amongst 60 of these isolates selected for growth studies in cyclohexane (possibly associated with up-regulated efflux), only one isolate grew. From this isolate and the six isolates used in the adaptation and de-adaptation studies, mutants highly resistant to triclosan (a disinfectant linked with mar-type resistance) were selected. In addition, adaptation and de-adaptation studies with triclosan were performed. For the 286 isolates, the small variations in MICs could not be associated with Salmonella persistence in Danish broiler houses or previous use of relevant disinfectants. Adaptation and de-adaptation did not alter MICs to the five farm disinfectants. Compared to the parent isolates, MICs for the triclosan adapted and de-adapted isolates and the triclosan mutants were significantly increased to triclosan, but not to the five disinfectants. Moreover, most of the triclosan adapted and de-adapted isolates grew in cyclohexane. Thus, there was no correlation between triclosan and cyclohexane resistance on one hand and resistance to the five disinfectants on the other, suggesting that triclosan resistance is not linked with resistance to these disinfectants.