Enterococci as Members of the Intestinal Microflora of Humans

Three molecular analytical approaches based on small ribosomal subunit RNA (16S rRNA) sequences have proven to be able to provide reliable knowledge about the richness (diversity of species) and evenness (population sizes) of the fecal microflora of humans. These approaches are phylogenetic analysis by PCR, cloning, sequencing; total fluorescent in situ hybridization (FISH) analysis using oligonucleotide probes that target specific 16S rRNA sequences; and oligonucleotide/total bacterial RNA hybridizations on membranes. Relatively well-described examples of the biological succession that occurs in the infant gut are provided by investigations of the acquisition of the intestinal microflora by mice and humans. Enterococci are inherently more resistant to antimicrobial drugs than other clinically important gram-positive bacteria, but the reason for this is not clear. Enterococci inhabit the gastrointestinal tract or environments contaminated by human waste and as such may be exposed to antibiotics that pass through the gastrointestinal tract. It is unlikely that enterococcal species experience selection with respect to antibacterial drugs during human infections. On the basis of these observations, it can be assumed that the intrinsic resistance of enterococci to many antimicrobials might have resulted from their need to survive and persist in highly competitive, and potentially detrimental, ecosystems such as the intestinal tract. The impact of imipenem on the composition of the intestinal microflora is, however, worthy of attention because enterococci have been isolated more frequently from pediatric cases of septicemia after the introduction of antibacterial drug.