Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2013
Publication Date: 2/1/2013
Citation: Kautz, M.J., Dvorzhinskiy, A., Frye, J.G., Stevenson, N., Herson, D.S. 2013. Pathogenicity of Dodecyltrimethylammonium Chloride-Resistant Salmonella enterica. Applied and Environmental Microbiology. 79(7):2371-2376. Interpretive Summary: Salmonella infection causes a self-limiting gastroenteritis in humans. The prevalence of antimicrobial and multidrug resistant Salmonella has increased worldwide since the 1980’s. However, the effect of antimicrobial resistance on the development of illness after ingesting Salmonella strains is not well described. In our study, we screened for differences in gene expression between a parental strain capable of causing disease and four strains of Salmonella that were modified by exposure to the antimicrobial sanitizer dodecyltrimethylammonium chloride (DTAC), until the strains were less susceptible to DTAC (Reduced Susceptibility Strains (SRS)). DATC is commonly found in soaps, shampoos, and sanitizers. Gene expression was detected using a technique called microarray. Two bacterial genes which showed differences in expression between the two parental and SRS strains were fimbriae (hair like structures on the bacteria’s surface) responsible for adhesion to host cells or associated with host cell invasion; a third gene with differences in expression was responsible for a protein which is important for bacterial growth inside host cells. Use of transmission electron microscopy determined that the fimbriae were absent in the four SRS strains, but abundant in the virulent parental strain. All four SRS strains had a significantly reduced ability to invade host cells in tissue culture as compared to the parental strains. These studies demonstrate that the development of resistance to antimicrobial sanitizer in these strains also resulted in reduced ability to grow in host cells. Therefore, the use of these sanitizers may result in in decreasing the likelihood of Salmonella causing severe illness. These observations should be considered when developing antimicrobial treatments for sanitizing work areas contaminated with Salmonella.
Technical Abstract: Salmonella infection causes a self-limiting gastroenteritis in humans but can also result in a life threatening invasive disease especially in old, young and/or immunocompromised patients. The prevalence of antimicrobial and multidrug-resistant Salmonella has increased worldwide since the 1980’s. However, the impact of antimicrobial resistance on the pathogenicity of Salmonella strains is not well described. In our study, a microarray was used to screen for differences in gene expression between a parental strain and a strain of Salmonella enterica serovar Enteritidis with Reduced Susceptibility (SRS) to the widely used antimicrobial sanitizer dodecyltrimethylammonium chloride (DTAC), which is commonly found in soaps, shampoos, sanitizers and other commercially produced cleansers. Three of the genes that showed differences in gene expression of two fold or greater, that are associated with adhesion, invasion and intracellular growth (fimA, csgG and spvR), were chosen for further study. Real time RT-PCR was used to confirm the microarray data and to compare the expression levels of these genes in the parental strain and four independently derived SRS strains. All SRS strains showed lower levels of gene expression of fimA and csgG as compared to the parental strain. Three of the four SRS strains showed lower levels of spvR gene expression while one SRS strain showed higher levels of spvR gene expression compared to the parental strain. Transmission electron microscopy determined that fimbriae were absent in the four SRS strains, but copiously present in the parental strain. All four SRS strains demonstrated a significantly reduced ability to invade tissue culture cells as compared to the parental strains, suggesting reduced pathogenicity of the SRS strains in vitro.