The effects of reduced susceptibility of Salmonella enterica to DTAC on some indicators of pathogenicity
Date
2010
Authors
Journal Title
Journal ISSN
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Publisher
University of Delaware
Abstract
The reduced susceptibility of microorganisms to biocides due to repeated or
continuous exposure is an ongoing area of study and may be a potential public health
concern. The reason for concern is from the possibility of a decrease in susceptibility
to antibiotics accompanying reduced susceptibility to biocides, especially for
pathogenic microorganisms. This study compares a parental strain of Salmonella
enterica with four strains derived from it, which have Reduced Susceptibility (SRS) to
the biocide dodecyltrimethylammonium chloride (DTAC). Quaternary Ammonium
Compounds (QACs) such as DTAC are commonly used in a wide range of cleaning
products. The minimal inhibitory concentrations (MICs) of the SRS strains were
above the concentration of DTAC recommended for cleaning products. A microarray
gene expression study of one of the SRS strains indicated that expression differed in
one third of the genome between the SRS strain and the parental strain. A few
indicators of pathogenicity were chosen for further comparison between the parental
and SRS strains; these were invasion, fimbriae, gene expression, biofilm formation
and growth patterns. All four SRS strains showed 100 fold fewer invasive cells in a
Caco-2 cell culture model. The SRS strains had lower levels of transcription of the fimbrial genes fimA and csgG measured by real time reverse transcriptase PCR and
produced fewer fimbriae as observed by transmission electron microscopy. The
transcription levels of the virulence regulator spvR which regulates the growth rate of
Salmonella post internalization was lower in three of the four SRS strains than in the
parental strain. The efflux pump gene associated with reduced susceptibility, acrB,
was upregulated in all four of the SRS strains. The SRS strains produced biofilm both
in the presence and absence of DTAC,whereas the parental strain was less affected by
the presence of DTAC. Growth in liquid culture was similar for the SRS and parental
strains. At a level of 150 percent of their respective MICs the parental and the SRS
strains were killed by DTAC. This finding shows that periodic sanitation using high
concentrations of DTAC could effectively control the growth and spread of these SRS
strains. Though the individual indicators of pathogenicity studied here the SRS strains
appear to be less pathogenic than the parental strain, this notion still must be
confirmed with animal studies given the magnitude of genes with different expression
levels as seen in the microarray.