Occurrence, Diversity of Listeria spp. Isolates from Food and Food-Contact Surfaces and the Presence of Virulence Genes.

Franca Rossi,Carmela Amadoro,Giampaolo Colavita,Valerio Giaccone,Daniele Conficoni

doi:10.3390/microorganisms8020294

Abstract

This study evaluates the hazards posed by foodborne bacteria of the Listeria genus by analyzing the occurrence, diversity and virulence of Listeria 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 L. monocytogenes virulence determinants occasionally found to occur in other species of the genus. Within this sample, 76% (n = 57) isolates were identified as L. innocua, 16% (n = 12) as L. monocytogenes, 6.6% (n = 5) as L. welshimeri and 1.3% (n = 1) as L. seeligeri. All L. monocytogenes isolates belonged to the serotype 1/2a and were predicted to be virulent for the presence of the inlJ internalin gene. Potentially virulent strains of L. innocua, L. seeligeri and L. welshimeri, carrying the L. monocytogenesinlA gene and/or hly gene, were identified, and most isolates were found to possess the toxin–antitoxin system mazEF for efficient adaptation to heat shock. Results indicated the need to reinforce food-contamination-prevention measures against all Listeria species by defining efficiently their environmental distribution.

Highlights

Bacteria belonging to the low-G+C facultatively anaerobic, Gram-positive Listeria genus are ubiquitous and can contaminate food products of both animal and plant origin [1].The human pathogen Listeria monocytogenes can cause severe foodborne infections, including septicemia, meningitis and endocarditis, with fatality rates of 20–30% in the elderly, immunocompromised persons and pregnant women, with infection in the latter resulting in abortion or neonatal infections [2]
Numerical analysis of rep-PCR profiles enabled the distinction of three main clusters exhibiting comparable internal diversity, each comprising exclusively of L. innocua, L. monocytogenes or L. welshimeri isolates, as ascertained by sequencing the 16S rRNA gene, with the exception of L. welshimeri 81 that fell outside the group formed by the other L. welshimeri isolates
This study presents the results of Listeria spp. occurrence based on the analysis of hundreds of food products and food-contact surfaces in manufacturing plants, and, as such, provides an insight into the distribution of these bacteria and to consumer exposure

Summary

Introduction

The human pathogen Listeria monocytogenes can cause severe foodborne infections, including septicemia, meningitis and endocarditis, with fatality rates of 20–30% in the elderly, immunocompromised persons and pregnant women, with infection in the latter resulting in abortion or neonatal infections [2]. It grows at refrigeration temperatures, under vacuum or in a modified atmosphere, tolerates low-pH values and forms sanitation-resistant biofilms in food-processing plants. L. monocytogenes must not reach levels higher than 100 CFU/g during their shelf life, while it must be absent from foods intended for infants or special medical purposes and from foods with aw and pH values that allow the growth of the bacterium up to the limit of 100 CFU/g during their shelf life [4]

Methods

Results

Conclusion