Improvement of the EN ISO 10273:2017 method for the cultural detection of Yersinia enterocolitica in meat

Abstract

The isolation of Yersinia enterocolitica from food is challenging, because the bacteria are readily overgrown by the concomitant microflora. In addition, thus far, no strictly selective medium for this species is available. The gold standard for cultural detection of Y. enterocolitica in food is described in the EN ISO 10273:2017. It includes a direct plating step that only enables the detection of large numbers of yersiniae. In addition, plating of the bacteria after selective enrichment for two days and a treatment with potassium hydroxide is mandatory. This approach may be critical, if the sample is highly contaminated with bacteria. Due to these limitations we improved the ISO procedure by adding a filtration and centrifugation step together with shortening the enrichment to only 6 h. This approach allowed a (i) more sensitive cultural detection than direct plating, (ii) limitation of background bacteria and (iii) saving of two days. The performance of the procedure was evaluated on minced meat samples, purchased at five supermarkets in Germany that were spiked with different numbers down to 4–6 cfu of a bioserotype B4/O:3 strain. Regardless of the background bacteria, the added strain could be isolated from every spiked sample. Moreover, biotype 1A isolates and other Yersinia species were recovered from some samples.