# Assessing mutation accumulation in DNA repair-deficient Listeria monocytogenes: implications for cgMLST cluster thresholds in outbreak analysis

## TL;DR

This study examines how DNA repair deficiencies in Listeria monocytogenes affect mutation rates and the accuracy of outbreak detection using cgMLST thresholds.

## Contribution

The study reveals that DNA repair-deficient Listeria strains accumulate mutations faster, potentially misclassifying related isolates in outbreak analysis.

## Key findings

- Mutation rates in DNA repair-deficient Listeria monocytogenes exceed typical cgMLST thresholds.
- Hypermutator strains may require adjusted cgMLST thresholds for accurate outbreak detection.
- DNA repair deficiencies are rare in clinical Listeria isolates.

## Abstract

Listeria (L.) monocytogenes is primarily transmitted via contaminated food and can cause listeriosis, an infection often associated with sepsis and meningitis in at-risk individuals. Accurate outbreak detection relies on whole genome sequencing (WGS) and core genome multilocus sequence typing (cgMLST), which use allele thresholds to identify related strains.

This study investigated mutation rates in L. monocytogenes, focusing on isolates with DNA repair deficiencies. Serial subcultivations were performed, comparing a repair-deficient isolate with a wild-type control. Genetic variability was assessed using WGS and cgMLST.

Mutation rates were significantly higher in repair-deficient isolates, exceeding typical cgMLST thresholds currently used in Listeria outbreak investigations, leading to a misclassification of related isolates as unrelated. An additional analysis of the Austrian Listeria database revealed that such deficiencies are rare among isolates.

The standard 7-allele cgMLST threshold effectively identifies related strains in most cases, but may require adjustments for hypermutator strains. Incorporating DNA repair data could improve the accuracy of outbreak investigations, ensuring reliable public health responses.