Listeria monocytogenes persister cells formation triggered upon antimicrobial exposure

Persister cells are a sub-population of growth-arrested bacteria with ability to transiently tolerate bactericidal levels of antimicrobial agents. While they do not replicate in the presence of these agents, they can persist during the exposure and later restore to an active, growing state under favorable conditions. This ability may contribute to the persistence of foodborne pathogens, such as Listeria monocytogenes, within food and feed production environments (FFPE). Therefore, this study aimed to investigate the formation of persister cells in two L. monocytogenes strains isolated from a dairy food production environment, previously characterized as persistent (Lm 2116) and non-persistent (Lm 1712). Both strains were exposed to high concentrations of gentamicin and nisin for 2, 4, and 6 hours. The results revealed a biphasic killing curve for both strains, a fundamental characteristic of persister cells, with a substantial reduction of the susceptible population at the earliest time point, followed by stabilization and selection of the persister bacterial sub-population over the 6-hour incubation period. These findings demonstrate that both antimicrobial agents, which operate through distinct mechanisms, can be successfully used to select L. monocytogenes persister cells from isolates derived from food industrial environments. This selection methodology may open new paths for research into persister cells and contribute to a better understanding of the adaptive phenotypic traits that enable certain strains to persist in FFPE, in comparison to non-persistent ones.