A novel cgMLST for genomic surveillance of infections in France allowed the detection and investigation of outbreaks in 2017-2021.

UNLABELLED

Enteric yersiniosis, the third most common food-borne zoonosis in Europe, is mainly caused by the pathogen . In France the yersiniosis microbiological surveillance is conducted at the National Reference Laboratory (YNRL). Since 2017, isolates have been characterized by whole genome sequencing (WGS) followed by a 500-gene -cgMLST. We report here the data of the WGS-based surveillance on isolates for the 2017-2021 period. The YNRL characterized 7,642 strains distributed in 2,497 non-pathogenic isolates from lineages 1Aa and 1Ab, and 5,145 specimens belonging to 8 pathogenic lineages. Among pathogenic isolates, lineage 4 was the most common (87.2%) followed by lineages 2/3-9b (10.6%), 2/3-5a (1.2%), 2/3-9a (0.6%), 3-3b, 3-3c, 1B, and 3-3d (0.1% per each). Importantly, we developed a routine surveillance system based on a new typing method consisting of a 1,727-genes core genome Multilocus Sequence Typing (cgMLST) specific to the species followed by isolate clustering. Thresholds of allelic distances (AD) were determined and fixed for the clustering of isolates: AD ≤ 5 for lineages 4, 2/3-5a, and 2/3-9a, and AD ≤ 3 for lineage 2/3-9b. Clustering programs were implemented in 2019 in routine surveillance to detect genomic clusters of pathogenic isolates. In total, 419 clusters with at least 2 isolates were identified, representing 2,504 of the 3,503 isolates characterized between 2019 and 2021. Most clusters ( = 325) comprised 2 to 5 isolates. The new typing method proved to be useful for the molecular investigation of unusual grouping of cases as well as for the detection of genomic clusters in routine surveillance.

IMPORTANCE

We describe here the new typing method used for molecular surveillance of infections in France based on a novel core genome Multilocus Sequence Typing (cgMLST) specific to species. This method can reliably identify the pathogenic subspecies and compare the isolates with a high discriminatory power. Between 2017 and 2021, 5,145 pathogenic isolates belonging to 8 lineages were characterized and lineage 4 was by far the most common followed by lineage 2/3-9b. A clustering program was implemented, and detection thresholds were cross-validated by the molecular and epidemiological investigation of three unusual groups of infections. The routine molecular surveillance system has been able to detect genomic clusters, leading to epidemiological investigations.