Antibiotic resistance and molecular characterization of probiotic and clinical Lactobacillus strains in relation to safety aspects of probiotics.

The evaluation of the safety of probiotic strains includes the exclusion of antibiotic resistance of clinical importance. Ninety-two strains from the genus Lactobacillus isolated from probiotics, food, and clinical sources were included in the investigation. Species tested were the L. acidophilus group, L. casei group, L. reuteri/fermentum group, and L. sakei/curvatus group. Cell and colony morphology, fermentation patterns, and growth characteristics as well as soluble whole cell proteins were analyzed. Antibiotic resistance against clinically important agents was determined by broth dilution tests. The vanA and tet genes were confirmed. Resistances occurred mainly against gentamicin, ciprofloxacin, clindamycin, sulfonamides, and, in some cases, glycopeptides. The natural glycopeptide resistance within the L. casei group and L. reuteri appears to be not of clinical relevance, as there was no vanA gene present. Therefore, the transfer of this resistance is very unlikely. Tet-(A), -(B), -(C), -(M), or -(O) gene could not be detected. The protein fingerprinting within the L. casei group proved that L. rhamnosus strains of clinical origin clustered together with probiotic strains. For safety evaluations resistance patterns of a broad range of strains are a useful criterion together with the exclusion of known resistance genes (like the vanA gene) and can be used for decision making on the safety of probiotics, both by authorization bodies and manufacturers.