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

Antibiotic resistance (AR) represents a global concern for human health. To the best of the authors' knowledge, no study addressing AR in , a traditional Swedish fermented herring, has been performed to date. The aim of the present research was to study the prevalence of (O), (S), (W), (K), and (M) genes encoding for resistance to tetracycline using quantitative PCR (qPCR) applied to ready-to-eat samples collected from three producers located in Sweden. The (M) gene was found in all the analyzed samples, and it was also the most abundant among the tested genes; moreover, (O) was the least frequently detected gene. As a general trend, all the analyzed samples showed a high occurrence of the target genes, with slight variations among the producers. A principal component analysis did not reveal any separation among the samples or producers. All the collected data allowed for a drawing of a first picture of the occurrence of tetracycline resistance genes in ready-to-eat samples. Since no differences among the samples manufactured by the different producers were observed, it is likely that the detected genes were homogeneously spread among the microbial species shared by the herrings used as raw materials. Moreover, it can be hypothesized that the presence of the detected genes was also the result 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 . However, the contribution of the manufacturers to the contamination of the processed herrings cannot be excluded.