Simultaneous detection of Bacteroides fragilis group species by leuB -directed PCR

Bacteroides species, saccharolytic Gram-negative obligate anaerobes, are frequently isolated from human infections such as peritonitis, abscesses and bacteremia. Among the species in the genus Bacteroides, thespecies called “B. fragilis group” areparticularly involved inhuman infections andaremedically important because they account for a major part of anaerobic isolates from clinical specimens. The purpose of this study was to develop PCR primers that specifically and simultaneously amplify theβ-isopropylmalate dehydrogenase gene leuB in B. fragilis group species. We determined partial nucleotide sequences of leuB genes and compared them in seventeen strains of nine B. fragilis group species, and the regions that are conserved among Bacteroides strains but different from other species were used as a B. fragilis group-specific PCR primer set, BacLBF-BacLBR. Specificity tests of the primer set using 52 phenotypically characterized strains and 75 isolates from rat feces showed only one case each of false-positive and falsenegative. The detection limit of the leuB-directed PCR using BacLBF and BacLBR was 3.9×103colony-forming units. These results indicate that leuB amplification using BacLBF and BacLBR is a useful tool for rapid diagnosis of Bacteriodes infection and for rapid differential diagnosis of anaerobic infections.