AEM Accepts, published online ahead of print on 6 November 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.00925-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Sub-lethal concentrations of common disinfectants influence virulence gene expression in Listeria monocytogenes

Vicky G. Kastbjerg^*, Marianne Halberg Larsen, Lone Gram, and Hanne Ingmer

National Institute of Aquatic Resources, Technical University of Denmark, Søltofts Plads bldg. 221, DK-2800 Kgs. Lyngby, Denmark; Department of Veterinary Disease Biology, Faculty of Life Sciences, University of Copenhagen, Stigbøjlen 4, DK-1870 Frederiksberg, Denmark

^* To whom correspondence should be addressed. Email: vgk{at}aqua.dtu.dk.

Listeria monocytogenes is a food-borne human pathogen that causes listeriosis, a relative rare infection with a high fatality rate. The regulation of virulence gene expression is influenced by several environmental factors, and the aim of the present study was to determine how disinfectants, used routinely in the food industry, affect the expression of different virulence genes in L. monocytogenes when added in sub-lethal concentrations. An agar-based assay was developed to screen the effect of disinfectants on virulence gene promoter expression and was validated at the transcriptional level by Northern blot analysis. Eleven disinfectants representing four different groups of active components were evaluated in this study. Disinfectants with the same active ingredients caused a similar effect on gene expression. Peroxy- and chlorine compounds reduced the expression of the virulence genes and quaternary ammonium compounds (QAC) induced the expression of the virulence genes. In general, a disinfectant had similar effect on the expression on all four virulence genes examined. Northern blot analyses confirmed the down-regulation of prfA and inlA expression by Incimaxx DES (a peroxy compound) and the up-regulation by Triquart SUPER (a QAC) in L. monocytogenes EGD. Hence, sub-lethal concentrations of disinfectants routinely used in the food industry affect virulence gene expression in the human pathogen L. monocytogenes, and the effect depend on the active components of the disinfectant. From a practical perspective, the study underlines that disinfectants should be used in the lethal concentrations recommended by the manufactures. Further studies are needed to elucidate if the change in virulence gene expression induced by the disinfectants have impact on virulence or other biological properties such as antibiotic resistance.