Can Listeria monocytogenes Growth Variability be Explained By the Genotype?

Introduction:  Listeria monocytogenes is a microbial pathogen that causes the foodborne listeriosis. This pathogen is able to survive and grow under a wide range of environmental stressfil conditions (low temperature, pH and aw) often found in food processing plants or during food storage. Intraspecific strain variability, although limited, has already been demonstrated in literature but reasons explaining these differences are scarce or contradictory between studies.

Purpose:  The aim of this study was to look for a potential link between the phenotype (growth rate, µ_max, under stressful environments) and the genotype (based on Pulsed Field Gel Electrophoresis; PFGE).

Methods:  The µ_max of 53 strains of L. monocytogenes was determined by optical density measurement in different harsh conditions; i.e. cold (8°C), acid (pH 5, 20°C), and low water activity (aw 0.95, 20°C). A reference strain was used to assess inter-experimental variability. For each condition, clustering of strains was established based on µ_maxvalues and dendrograms were drawn. PFGE profiles (based on AscI/ApaI restriction enzymes) were obtained for all these strains and a phylogentic tree was established according to UGPMA algorithm. Finally all created trees were compared among each other. A statistical analysis of the relationships between the trees/dendrograms was conducted in order to look for a possible link between pheno- and genotype.

Results: A relationship could not be observed under the tested conditions between the PFGE based tree and the µ_maxvalues for each condition. Even the comparisons of the three phenotype dendrograms displayed no similarity.

Significance:  The next step will be a comparison involving a genotype characterization, based on the whole genome sequence. An existing relationship between pheno- and genotype could help predict microbial behavior during food processing and storage; and thus, introduce genomics in risk assessment.