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Listeria monocytogenes strains which are underrepresented during selective enrichment with the ISO method might dominate during passage through simulated gastric fluid and in vitro infection of Caco-2 cells.

ABSTRACT: Various Listeria monocytogenes strains may contaminate a single food potentially resulting in simultaneous exposure of consumers to multiple strains. However, L. monocytogenes strains isolated from foods by selective enrichment (SE) might not always represent those that can better survive a patient immune system, due to bias in strain recovery. We investigated the effect of co-cultivation in TSB-Y at 10°C for 8 days on i) the detection of L. monocytogenes strains during SE with the ISO 11290-1:1996/Amd 1:2004 protocol and ii) the in vitro virulence of strains towards the human colon epithelial cancer cell line Caco-2 following exposure to simulated gastric fluid (SGF, pH 2.0/HCl, 37°C). We determined whether the strains, which were favoured by SE, would be effective competitors under challenges related to gastrointestinal passage of the pathogen. Inter-strain competition of L. monocytogenes in TSB-Y determined the relative population of each strain at the beginning of SE. This in turn impacted the outcome of SE (i.e., favoring survival of better fitness competitors) and the levels exposed subsequently to SGF. However, strong growth competitors could be outcompeted after SGF exposure and infection of Caco-2 cells by strains outgrown in TSB-Y and underdetected (or even missed) during enrichment. Our data demonstrate a preferential selection of certain L. monocytogenes strains during enrichments, often not reflecting a selective advantage of strains during infection. These findings highlight a considerable scenario associated with the difficulty to match the source of infection (food) with the L. monocytogenes isolate appearing as the causative agent during listeriosis outbreak investigations.This study is relevant to understanding the processes involved in selection and prevalence of certain L. monocytogenes strains under different environments (i.e foods or sites of humans exposed to the pathogen). It highlights the occurrence of multiple strains in the same food as an important aspect contributing to mismatches between clinical isolates and infection sources during listeriosis outbreak investigations.

SUBMITTER: Zilelidou E

PROVIDER: S-EPMC5103084 | biostudies-other | 2016 Sep

REPOSITORIES: biostudies-other

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Listeria monocytogenes Strains Underrepresented during Selective Enrichment with an ISO Method Might Dominate during Passage through Simulated Gastric Fluid and In Vitro Infection of Caco-2 Cells.

Zilelidou Evangelia E Karmiri Christina-Vasiliki CV Zoumpopoulou Georgia G Mavrogonatou Eleni E Kletsas Dimitris D Tsakalidou Effie E Papadimitriou Konstantinos K Drosinos Eleftherios E Skandamis Panagiotis P

Applied and environmental microbiology 20160916 23

Various Listeria monocytogenes strains may contaminate a single food product, potentially resulting in simultaneous exposure of consumers to multiple strains. However, due to bias in strain recovery, L. monocytogenes strains isolated from foods by selective enrichment (SE) might not always represent those that can better survive the immune system of a patient. We investigated the effect of cocultivation in tryptic soy broth with 0.6% yeast extract (TSB-Y) at 10°C for 8 days on (i) ...[more]

PMID: 27637880

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Project description:In this study, we addressed different aspects regarding the implementation of quasimetagenomic sequencing as a hybrid surveillance method in combination with enrichment for early detection of Listeria monocytogenes in the food industry. Different experimental enrichment cultures were used, comprising seven L. monocytogenes strains of different sequence types (STs), with and without a background microbiota community. To assess whether the proportions of the different STs changed over time during enrichment, the growth and population dynamics were assessed using dapE colony sequencing and dapE and 16S rRNA amplicon sequencing. There was a tendency of some STs to have a higher relative abundance during the late stage of enrichment when L. monocytogenes was enriched without background microbiota. When coenriched with background microbiota, the population dynamics of the different STs was more consistent over time. To evaluate the earliest possible time point during enrichment that allows the detection of L. monocytogenes and at the same time the generation of genetic information that enables an estimation regarding the strain diversity in a sample, quasimetagenomic sequencing was performed early during enrichment in the presence of the background microbiota using Oxford Nanopore Technologies Flongle and Illumina MiSeq sequencing. The application of multiple displacement amplification (MDA) enabled detection of L. monocytogenes (and the background microbiota) after only 4 h of enrichment using both applied sequencing approaches. The MiSeq sequencing data additionally enabled the prediction of cooccurring L. monocytogenes strains in the samples. IMPORTANCE We showed that a combination of a short primary enrichment combined with MDA and Nanopore sequencing can accelerate the traditional process of cultivation and identification of L. monocytogenes. The use of Illumina MiSeq sequencing additionally allowed us to predict the presence of cooccurring L. monocytogenes strains. Our results suggest quasimetagenomic sequencing is a valuable and promising hybrid surveillance tool for the food industry that enables faster identification of L. monocytogenes during early enrichment. Routine application of this approach could lead to more efficient and proactive actions in the food industry that prevent contamination and subsequent product recalls and food destruction, economic and reputational losses, and human listeriosis cases.

Dataset Information

Listeria monocytogenes strains which are underrepresented during selective enrichment with the ISO method might dominate during passage through simulated gastric fluid and in vitro infection of Caco-2 cells.

Publications

Listeria monocytogenes Strains Underrepresented during Selective Enrichment with an ISO Method Might Dominate during Passage through Simulated Gastric Fluid and <i>In Vitro</i> Infection of Caco-2 Cells.

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