P2-51 Desiccation of Listeria monocytogenes Biofilms Reveals an Association between Survival and the Presence of Clonal Complex 8, Listeria Genomic Island 1, or Stress Survival Islet Gene Markers, in Outbreak and Environmental Strains

Tuesday, August 5, 2014
Exhibit Hall D (Indiana Convention Center)
Marta Piercey, Dalhousie University, Halifax, Canada
Lisbeth Truelstrup Hansen, Dalhousie University, Halifax, Canada
Introduction: Listeria monocytogenes is a pathogenic foodborne microorganism noted for its ability to persist for long periods in the environment and food processing facilities. Persistence has been attributed to the bacterium’s ability to form biofilms but may also be related to desiccation resistance.

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.