Purpose: The purpose of this study was to characterize the desiccation survival in biofilms formed by environmental and outbreak associated strains of L. monocytogenes.
Methods: Pre-formed biofilms of 15 outbreak and environmental Listeria monocytogenes strains (serotype 1/2) were desiccated on stainless steel coupons at ~48% relative humidity at 15°C. Viable counts were determined over the course of 21 days. Presence of genetic markers indicative of strains harbouring the stress survival islet (SSI-1), the 50 kbp Listeria genomic island (LGI1), and clonal complex 8, virulence type 59 (CC8/VT59 ) associated with previous Canadian outbreaks, were determined by PCR.
Results: The most desiccation susceptible strains (>2-3 log CFU/cm2 reduction at 21 days) contained none of the SSI-1, LGI1, or CC8/VT59 markers. In contrast, the majority of strains exhibiting desiccation resistance by undergoing less than a 2-log CFU/cm2 reduction over the desiccation period of 21 days were observed to harbour at least one of the CC8/VT59, LGI1, and/or SSI-1 markers. Notably, the environmental origin (aquatic, food and human outbreak cases) of L. monocytogenes strains appeared to be unrelated to desiccation tolerance as one of the most resistant strains originated in a watershed, while some susceptible strains were isolated in food processing facilities or had caused foodborne illness.
Significance: This study revealed the possible involvement of genes previously associated with environmental persistence in the desiccation survival of Listeria monocytogenes biofilms on food grade stainless steel surfaces.