Purpose: This project was designed to identify the phenotypic and genotypic factors that support the survival and virulence of L. monocytogenes.
Methods: The genotypes and phenotypes of L. monocytogenes strains cultured from cantaloupe farm A, which were associated with the listeriosis outbreak and strains from farm B, which were not associated with any illnesses, were characterized using whole genomes sequencing and phenotypic microarray. Raw sequences were assembled using de novo approach and compared against one other. Phenotypic microarray results were analyzed using OmniLog software package with a cut-off value of ±3,000 OmniLog units.
Results: Genome sequencing analysis identified two unique regions (39 and 42 kbp) in the outbreak strain, in which over 60% of the genes were phage related. Function-based analysis revealed that the outbreak strain had 21 unique proteins, in particular 3 membrane transport proteins along with 2 invasion and intracellular resistance proteins. Phenotypic microarray analysis suggested that the outbreak strain had higher resistance to 3 osmolytes and 15 antimicrobial chemicals, whereas lower resistance to 11 pH conditions and 22 other antimicrobial chemicals along with lower growth in 11 carbon sources. The findings from phenotype comparisons appear to correlate well with genotype comparisons.
Significance: Comparative analysis of the genotypic and phenotypic characteristics will help elucidate mechanisms responsible for the survival and persistence of L. monocytogenes in food production environments, which may shed light on the development of effective preventive measures to control this pathogen in such environments.