Occurrence, Diversity of <i>Listeria</i> spp. Isolates from Food and Food-Contact Surfaces and the Presence of Virulence Genes
2020
Franca Rossi | Carmela Amadoro | Daniele Conficoni | Valerio Giaccone | Giampaolo Colavita
This study evaluates the hazards posed by foodborne bacteria of the <i>Listeria</i> genus by analyzing the occurrence, diversity and virulence of <i>Listeria</i> spp.in food and food-manufacturing plants. Seventy-five isolates obtained from the routine analysis of 653 samples taken by three diagnostic laboratories in Northern Italy were genotypically differentiated by Repetitive Extragenic Palindrome (rep) PCR, with the GTG5 primer identified by sequencing the 16S rRNA gene and examined by specific PCR tests for the presence of <i>L. monocytogenes</i> virulence determinants occasionally found to occur in other species of the genus. Within this sample, 76% (<i>n</i> = 57) isolates were identified as <i>L. innocua</i>, 16% (<i>n</i> = 12) as <i>L. monocytogenes</i>, 6.6% (<i>n</i> = 5) as <i>L. welshimeri</i> and 1.3% (<i>n</i> = 1) as <i>L. seeligeri</i>. All <i>L. monocytogenes</i> isolates belonged to the serotype 1/2a and were predicted to be virulent for the presence of the <i>inl</i>J internalin gene. Potentially virulent strains of <i>L. innocua</i>, <i>L. seeligeri</i> and <i>L. welshimeri</i>, carrying the <i>L. monocytogenesinl</i>A gene and/or <i>hly</i> gene, were identified, and most isolates were found to possess the toxin−antitoxin system <i>maz</i>EF for efficient adaptation to heat shock. Results indicated the need to reinforce food-contamination-prevention measures against all <i>Listeria</i> species by defining efficiently their environmental distribution.
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