New Aspects on Listeria monocytogenes ST5-ECVI Predominance in a Heavily Contaminated Cheese Processing Environment

Abstract

The eradication of Listeria monocytogenes from food chains is still a great challenge for the food industry and control authorities since some clonal complexes (CCs) are either better adapted to food processing environments (FPEs) or are globally widespread. In this work, we focus on the in-house evolution of L. monocytogenes genotypes collected from a heavily contaminated FPE whose contamination pattern underwent a massive and yet unexplained change. At the beginning of the sampling in 2010, a high variety of most likely transient L. monocytogenes genotypes was detected belonging to sequence type (ST) 1, ST7, ST21, ST37. After several efforts to intensify the hygiene measures, the variability was reduced to L. monocytogenes ST5 that was dominant in the following years 2011 and 2012. We aimed to elucidate possible genetic mechanisms responsible for the high abundance and persistence of ST5 strains in this FPE. Therefore, we compared the genomes of six L. monocytogenes ST5 strains to the less frequently occurring transient L. monocytogenes ST37 and ST204 from the same FPE as well as the highly abundant ST1 and ST21 isolated in 2010. Whole genome analysis indicated a high degree of conservation among ST5 strains [average nucleotide identity (ANI) 99.93–99.99%; tetranucleotide correlation 0.99998–0.99999]. Slight differences in pulsed field gel electrophoresis (PFGE) patterns of two ST5 isolates could be explained by genetic changes in the tRNA-Arg-TCT prophages. ST5 and ST204 strains harbored virtually identical 91 kbp plasmids related to plasmid group 2 (pLM80 and pLMUCDL175). Interestingly, highly abundant genotypes present in the FPE in 2010 did not harbor any plasmids. The ST5 plasmids harbored an efflux pump system (bcrABC cassette) and heavy metal resistance genes possibly providing a higher tolerance to disinfectants. The pLM80 prototype plasmids most likely provide important genetic determinants for a better survival of L. monocytogenes in the FPE. We reveal short-term evolution of L. monocytogenes strains within the same FPE over a 3 year period and our results suggest that plasmids are important for the persistence of ST5 strains in this FPE.

Genomic Diversity of Common Sequence Types of Listeria monocytogenes Isolated from Ready-to-Eat Products of Animal Origin in South Africa

“…The stress survival islets (SSI-1 and SSI2) are known to be responsible for the proliferation of L. monocytogenes under stressful conditions in food processing facilities [39,40]. In the current study, SSI-1 was detected in a E313 sample belonging to ST1 of lineage I. SSI-2 was present in two samples (E367 and E362) which belong to ST121 and ST204 of lineage II, respectively (Table 2).…”

“…The LIPI4 appears to be strongly associated with ST4 isolates [1]; hence, it was not observed in the current study. Several studies have identified mutations that are important in L. monocytogenes virulence markers [40,[56][57][58]. The analysis of all sequenced strains in the present study indicated that they all encode for full-length InlA and ActA proteins.…”

“…Listeria monocytogenes is equipped with mechanisms that allow it to adapt to and survive under stressful conditions [39]. However, there is a high degree of strain divergence in stress response and environmental adaptation, which is mostly associated with the presence of SSI-1 and SSI-2 [40]. According to Reference [39], SSI-1 supported the growth of L. monocytogenes under salt, acidic, bile, and gastric stress conditions and is overrepresented in human clinical isolates, whereas SSI-2 is mostly found in isolates from food and food-processing environments.…”

Dynamics of mobile genetic elements of Listeria monocytogenes persisting in ready-to-eat seafood processing plants in France

“…Multiple plasmid-borne homologous genes have been recently associated with lineage II food isolates [15]. Without a full description of the causal mechanisms promoting this particular phenotype, strains belonging to food-associated clonal groups of lineage II, including CC121, CC9, CC8, CC101, CC7 and CC204, have been shown to be persistent in FPEs [16][17][18][19][20][21][22].…”

“…For instance, the three-gene cassette bcrABC, located either on the chromosome or transposable units of L. monocytogenes strains, was described as conferring an increased resistance to BC, a widely used QAC disinfectant in the food industry in the past few decades [36]. The bcrABC cassette was detected in L. monocytogenes strains belonging to CC121, CC5, CC9, CC8, CC14 and CC204 [19,21,26] but not to CC7, CC101 and CC155 [18,26]. In addition, the transposon Tn6188 carrying the transporter QacH, and the transposon LGI1, carrying a small multidrug-resistant (SMR) efflux pump encoded by emrE, both responsible for enhanced BC tolerance, have been described as specific to CC121 and CC8 strains, respectively [35,37,38].…”