Collaboratrici e collaboratori

Bacterial strains used as starter cultures in the production of fermented foods may act as reservoirs for antibiotic resistance (AbR) genes. To avoid the introduction of such genes into the food chain, the presence of acquired AbR in bacterial strains added to food must be tested. Standard protocols and microbiological cut-off values have been defined to provide practitioners a basis for evaluating whether their bacterial isolates harbour an acquired resistance to a given antibiotic. Here, we tested the AbR of 24 strains of Pediococcus acidilactici using the standard protocol and microbiological cut-off values recommended by the European Food Safety Authority (EFSA). Phenotypic data were complemented by searching for known AbR genes using an in silico analysis of whole genomes. The majority of the strains (54.2%) were able to grow at a tetracycline concentration above the defined cut-off, even though only one carried a known tetracycline resistance gene, tetM. The same strain also carried the AbR gene of an erythromycin resistance methylase, ermA, and displayed resistance towards clindamycin and erythromycin. Our results bolster the scarce data on the sensitivity of P. acidilactici to tetracycline and suggest that the microbiological cut-off recommended by the EFSA for this antibiotic should be amended.