4-hour in vitro growth curves of a type III group B streptococcus (GBS) and Escherichia coli were examined in sterile term human amniotic fluid specimens. Both bacterial strains proliferated despite ratios of phosphate to elemental zinc in the range reportedly inhibitory for E. coli. After 4 h of incubation, despite comparable inocula, GBS numbers exceeded those of E. coli by 10-fold to 100-fold. The strikingly rapid growth of some GBS strains in amniotic fluid may represent yet another factor responsible for perinatal GBS infection of the human neonate.

The normal intestinal microflora plays pivotal roles in aiding with digestion, stimulating the immune system, and providing protection from enteric pathogens. Despite the importance of these organisms, they are often an innocent bystander, caught in the crossfire during antibiotic treatments intended to target and eliminate invading infectious agents. The collateral damage of antibiotic therapy is a reduction in the population of beneficial bacteria as well as an increased risk for more severe infections, including Clostridium difficile. Additionally, the unpleasant condition termed antibiotic-associated diarrhea is an unfortunate consequence of such treatments. In an attempt to alleviate the intestinal distress, individuals are turning to probiotic supplements, which consist of non-pathogenic bacteria purported to provide various health benefits, such as digestive regularity, prevention of disease, and replenishment of the natural microbiota of the human intestinal tract. However, if the bacterial strains present in the physician-recommended probiotic supplements are overly sensitive to antibiotics, then they would fail to reestablish the intestinal microflora during the course of treatment. The purpose of this project was to test the hypothesis that bacterial strains contained within probiotics are resistant to a variety of common antibiotics. Antibiotic susceptibility was assessed for several over-the-counter probiotic supplements via the Kirby-Bauer Disk Diffusion method on medium specific for lactobacilli propagation. After measuring the zones of inhibition, the probiotics were surprisingly sensitive to two-thirds of the antibiotics tested, with the observed growth inhibition greatly exceeding predetermined standards for susceptibility. These results suggest that concomitantly taking probiotic supplements during a course of antibiotics is likely futile for replenishing the intestinal microbiota. We intend to expand the study to include additional antibiotics and supplements of varying formulations in an attempt to gain insight into which strains may exhibit the least sensitivity and be the most effective for recolonization of the gastrointestinal tract.