Identification of genes induced in Listeria monocytogenes during growth and attachment to cut cabbage, using differential display.

The food-borne pathogen Listeria monocytogenes is a ubiquitous soil bacterium with the potential to contaminate fresh produce during cultivation and postharvest processing. In order to identify potential mechanisms by which L. monocytogenes may successfully attach to and colonize fresh produce, gene expression in L. monocytogenes cells inoculated onto fresh-cut cabbage was compared to gene expression in cells grown under control conditions. Differential display of reverse transcriptase PCR fragments amplified with a set of 81 arbitrary primers allowed the isolation and identification of 32 L. monocytogenes gene fragments that were observed to be more highly expressed under cabbage-associated conditions. Genes involved in carbohydrate, amino acid, and nucleic acid metabolism, motility and cell division, and transport were identified, as were a number of open reading frames (ORFs) encoding putative proteins with no known functions. Site-directed mutations in two ORFs encoding potential cell surface-associated proteins and a third ORF encoding a putative regulatory protein had no effect on the mutants' capacity to attach to fresh-cut cabbage. Although this study did not show clearly the impact of the differentially expressed genes on growth on cabbage, it is a first step in identifying some of the genetic factors that are potentially involved.