LISTADAPT: Adaptability of Listeria to different ecological niches.

Project description

The bacterium Listeria monocytogenes, together with Salmonella and toxin-producing E. coli bacteria (STEC), is the main cause of foodborne infections in the EU, measured by severity of illness and mortality rate. Since 2008, a significant increase in the incidence of listeriosis has been recorded in Europe, highlighting listeriosis as a serious recurrent health problem.

However, the ecology of Listeria monocytogenes is still poorly understood. The high adaptability of some strains to diverse ecological niches also makes the production of high quality, safe food a major challenge. The LISTADAPT project aims to elucidate which genes and molecular mechanisms underlie the adaptation of Listeria to diverse ecological niches.

The project used a combination of next generation sequencing (NGS) technology and phenotypic methods to compare data from a large and balanced number of Listeria strains. Twenty-one partners, including food, environmental, veterinary, and public health laboratories, were involved in generating a dataset of 1,575 strains and genomes of Listeria monocytogenes strains. These were collected in twenty European countries and cover many different habitats and diverse geographic regions.

Results

The LISTADAPT project has made 1,575 new Listeria monocytogenes genomes available to the scientific community. These genomes are representative of the different ecological niches and are now publicly available in the European Nucleotide Archive (ENA).

A subset of Listeria strains was used to test antimicrobial susceptibility to eleven antibiotics and four biocides. Results showed that strains isolated from food had overall higher minimum inhibitory concentrations for quaternary ammonium compounds (QACs) and peracetic acid (PAC) than strains isolated from animals and natural environments. Repeated exposure to QACs resulted in a decrease in susceptibility to ciprofloxacin, a fluoroquinolone antibiotic widely used in human and veterinary medicine and considered a critical antimicrobial agent. Mobile genetic elements were widespread in lineage I and II strains from food, highlighting the high adaptability of these Listeria strains, the nature of tolerance mechanisms, and the need to monitor these genes to reduce the risk of tolerant genotypes in the food industry.

This project was the first to report the presence of a CC121 strain isolated from a dolphin brain. Genomic analyses showed that 16 strains isolated from food were closest to the dolphin strain.

Summary

The LISTADAPT project was the first to study a large number of Listeria monocytogenes strains from a wide variety of European habitats. The antimicrobial susceptibility of Listeria to a range of antibiotics and biocides was also tested using a number of strains. The high adaptability of Listeria to ecological niches was also confirmed by the detection of mobile genetic elements in strains isolated from food. In order to keep the spread of Listeria in the food industry and thus the outbreak of listeriosis low, it is of importance to continue to continuously monitor developments in this field.

Benefit of the project

The collection of strains and genomes will be useful for follow-up projects and scientific questions. Detailed characterization of Listeria strains at the phenotypic and genotypic levels will help to assess the true importance of these strains as a source of foodborne infections for public health.