Tetracycline Resistance Patterns of Lactobacillus buchneri Group Strains.

Lactobacilli are applied as starter cultures for controlled fermentation in the production of food and feed. Among other lactobacilli, members of the Lactobacillus buchneri group are used in fermented milk, wine, and silage. Most of the L. buchneri species used for the manufacturing of food or feed are already on the list for qualified presumption of safety status and are recommended as biological agents by the European Food Safety Authority. Consequently, new strains intended as food or feed additives do not require any additional safety check than confirming the absence of transferable antibiotic resistance determinants. Of these determinants, tetracycline resistance genes are especially predominant in lactobacilli. Within this study, a total of 128 strains belonging to the L. buchneri group ( L. buchneri , L. diolivorans , L. farraginis , L. hilgardii , L. kefiri , L. kisonensis , L. otakiensis , L. parabuchneri , L. parafarraginis , L. parakefiri , L. rapi , L. senioris , and L. sunkii ) were examined for their susceptibility to tetracycline. Tetracycline MICs were assessed by the broth microdilution method according to ISO 10932/IDF 223. Subsequently, the presence of tetracycline resistance genes was investigated by using PCR. In addition, selected strains were tested for a broader range of tetracycline resistance genes by using a microarray technique. Applying the tetracycline cutoff values defined by European Food Safety Authority for heterofermentative and obligately homofermentative lactobacilli, 96.9% of the strains would have been categorized as tetracycline resistant. However, none of the tested tetracycline resistance genes could be detected by PCR or microarray analysis. Furthermore, the MIC distribution of all strains was unimodal and at the high end of the tested tetracycline concentration range (4 to 256 μg/ml). Thus, these data suggest that tetracycline resistance in the L. buchneri group strains is intrinsic, which complies with the requirements defined in the qualified presumption of safety outline.