Tetracycline Resistance Genes in the Traditional Swedish Sour Herring surströmming as Revealed Using qPCR

Antibiotic resistance (AR) represents a global concern for human health. To the best ofthe authors’ knowledge, no study addressing AR in surströmming, a traditional Swedish fermentedherring, has been performed to date. The aim of the present research was to study the prevalence oftet(O), tet(S), tet(W), tet(K), and tet(M) genes encoding for resistance to tetracycline using quantitativePCR (qPCR) applied to ready-to-eat surströmming samples collected from three producers located inSweden. The tet(M) gene was found in all the analyzed samples, and it was also the most abundantamong the tested tet genes; moreover, tet(O) was the least frequently detected gene. As a generaltrend, all the analyzed samples showed a high occurrence of the target genes, with slight variationsamong the producers. A principal component analysis did not reveal any separation among thesamples or producers. All the collected data allowed for a drawing of a first picture of the occurrenceof tetracycline resistance genes in ready-to-eat surströmming samples. Since no differences amongthe samples manufactured by the different producers were observed, it is likely that the detectedgenes were homogeneously spread among the microbial species shared by the herrings used as rawmaterials. Moreover, it can be hypothesized that the presence of the detected genes was also theresult of a selective pressure of the natural marine environment on the herrings’ gut microbiota and,hence, on the pro-technological microorganisms responsible for the fermentation of surströmming.However, the contribution of the manufacturers to the contamination of the processed herringscannot be excluded.