Biofilm Formation of Listeria monocytogenes Strains Under Food Processing Environments and Pan-Genome-Wide Association Study.

Bo-Hyung Lee,Stéphanie Badel-Berchoux,Sophie Cole,Benjamin Felix,Pascal Piveteau,Ibrahim Sultan,Laurent Guillier,Thierry Bernardi,Michel Hébraud,Nicolas Krezdorn

doi:10.3389/fmicb.2019.02698

Abstract

Concerns about food contamination by Listeria monocytogenes are on the rise with increasing consumption of ready-to-eat foods. Biofilm production of L. monocytogenes is presumed to be one of the ways that confer its increased resistance and persistence in the food chain. In this study, a collection of isolates from foods and food processing environments (FPEs) representing persistent, prevalent, and rarely detected genotypes was evaluated for biofilm forming capacities including adhesion and sessile biomass production under diverse environmental conditions. The quantity of sessile biomass varied according to growth conditions, lineage, serotype as well as genotype but association of clonal complex (CC) 26 genotype with biofilm production was evidenced under cold temperature. In general, relative biofilm productivity of each strain varied inconsistently across growth conditions. Under our experimental conditions, there were no clear associations between biofilm formation efficiency and persistent or prevalent genotypes. Distinct extrinsic factors affected specific steps of biofilm formation. Sudden nutrient deprivation enhanced cellular adhesion while a prolonged nutrient deficiency impeded biofilm maturation. Salt addition increased biofilm production, moreover, nutrient limitation supplemented by salt significantly stimulated biofilm formation. Pan-genome-wide association study (Pan-GWAS) assessed genetic composition with regard to biofilm phenotypes for the first time. The number of reported genes differed depending on the growth conditions and the number of common genes was low. However, a broad overview of the ontology contents revealed similar patterns regardless of the conditions. Functional analysis showed that functions related to transformation/competence and surface proteins including Internalins were highly enriched.

Highlights

Listeria monocytogenes is a psychrotolerant Gram-positive, rodshaped saprophytic bacterium
Biofilm production by 58 isolates was evaluated at 37◦C, the optimal growth temperature for L. monocytogenes and at 10◦C, a low temperature mimicking conditions in the food processing environments (FPEs)
Temperature played a major role in determining the total sessile biomass; in general, biofilm production was more than five times greater at 37◦C than at 10◦C with the exception of diluted BHI (dBHI) broth in which the total biomass produced at both temperatures was similar (Figures 1A,B)

Summary

Introduction

Listeria monocytogenes is a psychrotolerant Gram-positive, rodshaped saprophytic bacterium. As a non-fastidious organism, it tolerates a range of stressful conditions. Its resistance to high osmolarity was demonstrated by growth up to 13% NaCl and survival under 40% NaCl (Liu et al, 2005; Shabala et al, 2008). L. monocytogenes can grow at low temperatures (Junttila et al, 2008) and its minimal growth temperature is expected to be at −2◦C (Augustin et al, 2005). It withstands acidic and alkaline environments as well as low water activity conditions (Nolan et al, 1992; Koutsoumanis et al, 2003; Shen et al, 2016). Exposure to a stress factor can provide crossadaptation to subsequent exposure to other stresses (Begley et al, 2002; Bergholz et al, 2012)

Objectives

Methods

Results

Discussion

Conclusion