Pathogenicity of Dodecyltrimethylammonium Chloride-Resistant Salmonella enterica

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 1980s. 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). Three of the genes, associated with adhesion, invasion, and intracellular growth (fimA, csgG, and spvR), that showed differences in gene expression of 2-fold or greater were chosen for further study. Real-time reverse transcriptase PCR (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 than those of 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 than those of 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 compared to the parental strains, suggesting reduced pathogenicity of the SRS strains.