High Yersinia prevalence in tonsils of wild boars hunted in Northeast Germany using a novel protocol including long cold enrichment

In this study, the prevalence of Yersinia in wild boars in Northeast Germany was investigated. To also detect small numbers of the bacteria by the help of cold enrichment, tonsils of 81 wild boars hunted in 2023/2024 were stored for 12 weeks at 4°C, followed by freezing until usage. The presence of Yersinia in thawed tonsils was analyzed by cultural detection using a method based on a previously published protocol, including filtration and centrifugation steps and a selective enrichment for 6 h. Yersinia could be isolated from every animal. Yersinia enterocolitica and Yersinia pseudotuberculosis were recovered from 96% and 21% of the tonsils, respectively. In addition, we isolated eight other Yersinia species: Y. aleksiciae , Y. bercovieri , Y. frederiksenii , Y. intermedia , Y. kristensenii , Y. massiliensis , Y. mollaretii , and Y. rohdei ; the most prevalent of those was Y. kristensenii (41.9%). A total of 1,105 Y. enterocolitica isolates (1–116 per sample) were examined by multiplex PCR, revealing that two tonsils contained pathogenic Y. enterocolitica 1B/O:8, whereas all other isolates belonged to biotype (BT) 1A. One hundred eleven isolates were sequenced. The enterotoxin gene ystB was detected in every BT 1A isolate, while some of them additionally possessed the virulence genes ail , myfA , and tccC. Y. pseudotuberculosis isolates belonged to BT 1 or 2 and either to the sero/sequence type O:1a/42, O:1/43, or O:2a/14. The study suggests that wild boars are a natural reservoir for Yersinia and that the animals may be involved in their spread and in the contamination of vegetables like carrots and salad.