Listeria monocytogenes Grown at Refrigeration Temperature Shows Reduced Acid Survival and an Altered Transcriptional Response to Acid Shock

Survival of the foodborne pathogen Listeria monocytogenes in acidic environments (e.g., stomach and low pH foods) is vital to its transmission. L. monocytogenes grows at temperatures as low as 2°C, and refrigerated, ready-to-eat foods have been sources of L. monocytogenes outbreaks. The purpose of this study was to determine whether growth at a low temperature (i.e., 7°C) affects the response of L. monocytogenes to sudden acid shock. A full genome microarray was used to determine changes in L. monocytogenes 10403S gene expression after exposure to acidified brain-heart infusion (BHI; pH 3.5) for 5 or 15 min. To determine changes in gene transcription after acid treatment, separate competitive hybridizations were performed between cDNA from untreated cells (grown at 7°C or 37°C to log or stationary phase) and (i) cells acid treated for 5 min or (ii) cells acid treated for 15 min. For L. monocytogenes grown to log or stationary phase, competitive hybridizations were performed between total cDNA from non-acid-treated cells grown to 7°C and non-acid-treated cells grown to 37°C to determine baseline differences in gene transcription between growth temperatures prior to acid treatment. For each experiment, four biological replications were completed. Hybridizations were carried out with dye swapping (i.e., for each comparison, each cDNA from each condition was labeled with each dye exactly twice) to help minimize dye incorporation bias.