Reduced Susceptibility of Salmonella Enterica to Biocides

The use of biocides in clinical, industrial, and domestic settings has increased in recent years without enough research to fully assess the associated risks. Widespread exposure has raised concerns over the potential for microorganisms to develop resistance to biocidal agents. In this study, strains of Salmonella enterica were developed in the lab that exhibited stable, reduced susceptibility to dodecyl trimethylammonium chloride (DTAC), a commonly used quaternary ammonium compound, at levels higher than those found in domestic cleaning products. A strain was also developed to have reduced susceptibility to triclosan, another widespread biocidal agent. Several cellular properties of the strains with reduced susceptibility (SRS) and the Parent strain were studied and compared. These included fatty acid profiles, efflux pump activity, motility, and cross-resistance. SRS strains exhibited alterations in fatty acid composition, notably in cyclic and unsaturated fatty acids when compared to the Parent strain. When efflux pump activity was inhibited, reduced susceptibility was not maintained. Microscopy showed that SRS strains maintained flagella. However, motility agar plates and video monitoring showed that motility was inhibited, especially in the presence of DTAC. Strains with reduced susceptibility to both DTAC and triclosan exhibited cross-resistance to penicillin. This raises concerns that the overuse of biocides could contribute to antibiotic resistance in microorganisms.