Submitted to: American Society for Microbiology
Publication Type: Abstract Only
Publication Acceptance Date: 2/1/2009
Publication Date: 5/17/2009
Citation: Stevenson, N., Mierswa, M., Dvorzhinskiy, A., Frye, J.G., Herson, D. 2009. Salmonella enterica Strains with Reduced Susceptibility to Quarternary Ammonium Compounds. American Society for Microbiology. A029. Interpretive Summary:
Technical Abstract: Background: Salmonella spp. are responsible for 76 million illnesses per year in the U.S. Quaternary ammonium compounds (QAC) are commonly used antimicrobial agents. Reduced susceptibility to these compounds by a broad spectrum of organisms is a concern. Methods: Salmonella enterica strains with reduced susceptibility (SRS) to dodecyltrimethyl ammonium chloride (DTAC) were generated in our laboratory by repeated subculture in increasing concentrations of DTAC. The fatty acid profile (FAME), efflux pump activity, motility and gene expression (microarray analysis and Real Time rtPCR) of parental vs. SRS strains were compared. Results: FAME analysis indicated that SRS had increases in unsaturated fatty acids (16:1 w7c and 18:1 w7c) and decreases in cyclic fatty acids (17:0 cyclo and 19:0 cyclo w8c). Overall, higher UFA:SFA ratios suggested an increase in membrane fluidity. Based on differences in fatty acid content, the parent and SRS strains were determined to be different subspecies by principal component analysis. Microarray results indicated an increase in efflux pump expression and a decrease in pathogenicity expression (hilA, spvR and virK) in an SRS strain when compared to the parent. The upregulation of the acrB efflux pump was confirmed by RT-PCR in all SRS strains. In the presence of CCCP, an efflux pump inhibitor, the MICs for the SRS strains (is greater than 500 µg/ml DTAC) were reduced to levels below those of the parent (100 µg/ml). Laser scanning microscopy was used for motility tracking using the parental and SRS strains. All showed diminished motility in the presence of DTAC. In the absence of DTAC, the level of motility varied between the SRS strains, with none of these being more motile than the parent in either liquid culture or on semisolid media. All strains grown in the presence of DTAC possessed flagella. Conclusions: Of the many differences between the parent and SRS strains, increases in efflux pump activity and alterations in fatty acid content appear to be most essential for reduced susceptibility to QACs. The decrease in motility in the presence of DTAC may reflect a competition for the proton motive force which is utilized for both motility and efflux pump activity.