Genetic Subtyping, Biofilm-Forming Ability and Biocide Susceptibility of Listeria monocytogenes Strains Isolated from a Ready-to-Eat Food Industry.

Joana Catarina Andrade,Carlos De Sousa Alonso,Ana Rita Henriques,António Lopes João,António Salvador Barreto

doi:10.3390/antibiotics9070416

Joana Catarina Andrade, Carlos De Sousa Alonso + Show 3 more

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https://doi.org/10.3390/antibiotics9070416

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Abstract

Listeria monocytogenes is a foodborne pathogen of special concern for ready-to-eat food producers. The control of its presence is a critical step in which food-grade sanitizers play an essential role. L. monocytogenes is believed to persist in food processing environments in biofilms, exhibiting less susceptibility to sanitizers than planktonic cells. This study aimed to test the susceptibility of L. monocytogenes in planktonic culture and biofilm to three commercial food-grade sanitizers and to benzalkonium chloride; together with the genetic subtyping of the isolates. L. monocytogenes isolates were collected from raw materials, final products and food-contact surfaces during a 6-year period from a ready-to-eat meat-producing food industry and genetically characterized. Serogrouping and pulsed-field gel electrophoresis (PFGE) revealed genetic variability and differentiated L. monocytogenes isolates in three clusters. The biofilm-forming ability assay revealed that the isolates were weak biofilm producers. L. monocytogenes strains were susceptible both in the planktonic and biofilm form to oxidizing and ethanol-based compounds and to benzalkonium chloride, but not to quaternary ammonium compound. A positive association of biofilm-forming ability and LD90 values for quaternary ammonium compound and benzalkonium chloride was found. This study highlights the need for preventive measures improvement and for a conscious selection and use of sanitizers in food-related environments to control Listeria monocytogenes.

Highlights

Listeria monocytogenes is an ubiquitous small Gram-positive bacterium widespread in the natural environment [1]
All of the L. monocytogenes presumptive isolates (n = 20) obtained by conventional microbiological methods belonged to the Listeria genus, but only 17 were confirmed as L. monocytogenes by PCR [27]
This study provided an assessment of L. monocytogenes isolates from a RTE meat-based food industry, using phenotypic and genetic characterization

Summary

Introduction

Listeria monocytogenes is an ubiquitous small Gram-positive bacterium widespread in the natural environment [1]. It is an opportunistic pathogen responsible for human listeriosis, a severe disease with high hospitalization and case fatality rates [2,3]. Its psychrotrophic nature and the ability to survive and multiply under extreme physicochemical conditions [4] may explain the difficulty of controlling its presence in refrigerated environments [5]. This pathogen is often associated to ready-to-eat (RTE) food products, with contamination occurring during food processing production [6,7].

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