Identification and antibiotic susceptibility of bacterial isolates from probiotic products available in Italy

This study was carried out to assay the bacterial viability and the probable contamination of a range of probiotic products available in Italy and to test the susceptibility of the isolates. Eleven dried food supplements and five fermented functional foods were examined using different isolation media under standardized cultivation conditions. The identification was made by conventional phenotypic characteristics and biochemical tests. Among isolates from the probiotic products antibiotic susceptibility was detected using the E-test (ABBiodisk). Our results demonstrate that nine food supplements and two fermented foods claimed species which could not be isolated, whereas potential pathogens (i.e. Micromonas micros) were isolated. Lactobacilli displayed species-dependent antibiotic resistance. Atypical resistance occurred for penicillin in Lactobacillus acidophilus and Lactobacillus bulgaricus and for erythromycin in Lactobacillus lactis and Lactobacillus salivarius. A broad range of MICs was observed for cephalosporins and fluroquinolones. Aminoglycosides had poor activity against Lactobacillus isolates. Two of the four isolates of Bifidobacterium exhibited high resistance to trimethroprim/sulfametoxazole and to fluoroquinolones. Our results suggest that some probiotic products claim species that cannot always be isolated, and are sometimes contaminated by potential pathogens. Moreover, the probable transferable erythromycin or penicillin resistance among the lactobacilli isolated should be taken into account.