Assessment of antimicrobial susceptibility, intrinsic resistance, and virulence in industrially relevant bacteria

PhD Student: Katrine Nøhr-Meldgaard
Thesis defended: 18 October 2022

BACKGROUND

Whenever a bacteria is used for industrial purposes, it needs to be ensured that it is safe for the consumer and worker. Therefore, bacterial strains intentionally used for food, feed and probiotic production should not encode acquired antibiotic resistance genes as these potentially can transfer to other bacteria and compromise treatment of infections, while intrinsic resistance genes are not considered a safety concern. The strains should furthermore have a low risk of causing infection in humans or animals.

Much of the knowledge on antibiotic resistance and virulence come from the clinical area and pathogenic bacteria and interpretation criteria and tools specific for industrially relevant bacterial species are therefore needed to perform more objective and standardized strain safety assessments.

THE PROJECT

The project aimed at providing more knowledge and interpretation criteria on antimicrobial susceptibility, intrinsic resistance genes, and virulence in bacterial species for industrial purposes.

RESULTS 

The thesis provides improved cut-off values that follows phylogeny for industrially relevant bacteria including species belonging to Lactobacillus, Latilactobacillus, Ligilactobacillus, Lentilactobacillus, Limosilactobacillus, Pediococcus and Leuconostoc. The improved cut-off values will serve to ensure correct differentiation between strains encoding acquired antibiotic resistance genes and the susceptible strains within species. However, there is a need for sampling of more strains in order to provide relevant cut-off values for all industrially relevant bacterial species.

Phylogenetic and comparative analysis was used to examine antibiotic resistance gene evolution. The method enabled the differentiation between intrinsic antibiotic resistance genes, which are not considered a safety concern and the acquired antibiotic resistance genes that are at risk of being transferred to other bacteria and thereby compromise treatment of infections. The results show that phylogenetic analysis can be used for differenting between intrinsic and acquired antibiotic resistance genes.

In the present project, the virulence of industrially relevant bacteria was examined through genotypic and phenotypic assessment, with the aim of providing an improved assessment of virulence of industrially relevant bacterial species. The examined industrial relevant bacterial species did not encode any virulence factors, but several niche factors involved with survival rather than causing damage to the host. Further studies are needed in order to understand the mechanism involved with causing infections when non-pathogenic bacterial species are isolated in relation to infections.

The results and data generated through the PhD thesis will ensure a more objective and standardized strain safety assessment of industrially relevant bacteria.

For more info: katrine_3450@hotmail.com