Tetracycline susceptibility of the ingested Lactobacillus acidophilus LaCH-5 and Bifidobacterium animalis subsp. lactis Bb-12 strains during antibiotic/probiotic intervention.

We investigated the effects of oral therapy with doxycycline, a tetracycline group antibiotic, on the gastrointestinal (GI) survival and tetracycline susceptibility of probiotic strains Lactobacillus acidophilus LaCH-5 and Bifidobacterium animalis subsp. lactis Bb-12. In addition, the influence of doxycycline therapy on the diversity of the predominant faecal microbiota was evaluated by polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Faecal samples from the antibiotic group (receiving antibiotics and probiotics) and the control group (receiving probiotics only) were analysed for anaerobically and aerobically growing bacteria, bifidobacteria and lactic acid bacteria as well as for the dominant microbiota. Although doxycycline consumption did not have a large impact on GI survival of the probiotics, it had a detrimental effect on the bifidobacteria and on the diversity of the dominant faecal microbiota. A higher proportion of tetracycline-resistant anaerobically growing bacteria and bifidobacteria was detected in the antibiotic group than in the control group. Several antibiotic group subjects had faecal B. animalis subsp. lactis Bb-12-like isolates with reduced tetracycline susceptibility. This was unlikely to be due to the acquisition of novel tetracycline resistance determinants, since only tet(W), which is also present in the ingested B. animalis subsp. lactis Bb-12, was found in the resistant isolates. Thus, concomitant ingestion of probiotic L. acidophilus LaCH-5 and B. animalis subsp. lactis Bb-12 with the antibiotic did not generate a safety risk regarding the possible GI transfer of tetracycline resistance genes to the ingested strains.