The microbiota of the human genitourinary tract: trying to see the forest through the trees

Based on traditional microbiological methods, namely cultivation and microscopic analyses, the vaginal microbiota (VMB) has been defined as healthy when it is predominated by hydrogen peroxide-producing Lactobacillus spp., most prominently Lactobacillis crispatus. Similarly, the VMB has been defined as bacterial vaginosis (BV) when it is predominated by Gardnerella vaginalis as well as a number of other anaerobic bacterial species. BV is associated with a distinct vaginal discharge syndrome, poor pregnancy outcomes, pelvic inflammatory disease, post-operative wound infections, and endometritis after elective abortions. Additionally, BV predisposes women to infection by HIV as well as other sexually transmitted diseases (STDs). The application of molecular techniques over the last decade to studies of the VMB has significantly advanced our understanding of its structure and variation. It is now clear that the diversity of the VMB is far more complex than previously recognized; it is comprised of many heretofore unknown bacteria in addition to those previously identified by culture. Here we describe the application of 454 pyrosequencing technology to a study of vaginal specimens from 92 women attending the New Orleans STD clinic in an effort to obtain a more precise view of how different types of "trees" (bacteria) assemble to form a recognizable "forest" (VMB). This knowledge will be useful in the design of future clinical studies that investigate the mechanisms by which the vaginal microbiome influences human health and disease.