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. 2020 Jul 16;9(7):416.
doi: 10.3390/antibiotics9070416.

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

Joana Catarina Andrade  1 , António Lopes João  2 , Carlos de Sousa Alonso  2 , António Salvador Barreto  1 , Ana Rita Henriques  1
Affiliations

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

Joana Catarina Andrade et al. Antibiotics (Basel). .

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.

Keywords: Listeria monocytogenes; biocide; biofilm; planktonic culture; pulsed-field gel electrophoresis.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Dendrogram of the ApaI-AscI PFGE profiles and corresponding serogroup for 17 L. monocytogenes selected isolates.
Figure 2
Figure 2
Average and standard deviation of log cfu/mL and cvOD of 5-day L. monocytogenes biofilms.
Figure 3
Figure 3
Viable cell counts average and standard deviation (error bars) of the tested planktonic L. monocytogenes strains after treatment with BaC. (A) L. monocytogenes CECT 4031; (B) L. monocytogenes CECT 935; (C) L. monocytogenes RM1; (D) L. monocytogenes RM3; (E) L. monocytogenes RM5.
Figure 4
Figure 4
Average and standard deviation (error bars) of tested L. monocytogenes 5-day-old biofilms’ VCC after QaC treatment.
Figure 5
Figure 5
Viable cell counts average and standard deviation (error bars) of the tested L. monocytogenes 5-day-old biofilms after BaC treatment. (A) L. monocytogenes CECT 4031; (B) L. monocytogenes CECT 935; (C) L. monocytogenes RM1; (D) L. monocytogenes RM3; (E) L. monocytogenes RM5.
Figure 6
Figure 6
LD90 estimated values of L. monocytogenes tested strains in biofilm exposed to QaC.
Figure 7
Figure 7
LD90 estimated values of L. monocytogenes tested strains in biofilm and in the planktonic form exposed to BaC.
See this image and copyright information in PMC

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