The dissemination of C10 cysteine protease genes in Bacteroides fragilis by mobile genetic elements

Abstract

BackgroundThe C10 family of cysteine proteases includes enzymes that contribute to the virulence of bacterial pathogens, such as SpeB in Streptococcus pyogenes. The presence of homologues of cysteine protease genes in human commensal organisms has not been examined. Bacteroides fragilis is a member of the dominant Bacteroidetes phylum of the human intestinal microbiota, and is a significant opportunistic pathogen.ResultsFour homologues of the streptococcal virulence factor SpeB were identified in the B. fragilis genome. These four protease genes, two were directly contiguous to open reading frames predicted to encode staphostatin-like inhibitors, with which the protease genes were co-transcribed. Two of these protease genes are unique to B. fragilis 638R and are associated with two large genomic insertions. Gene annotation indicated that one of these insertions was a conjugative Tn-like element and the other was a prophage-like element, which was shown to be capable of excision. Homologues of the B. fragilis C10 protease genes were present in a panel of clinical isolates, and in DNA extracted from normal human faecal microbiota.ConclusionsThis study suggests a mechanism for the evolution and dissemination of an important class of protease in major members of the normal human microbiota.

The effect of environmental conditions on expression of Bacteroides fragilis and Bacteroides thetaiotaomicron C10 protease genes

“…We have previously demonstrated the transcriptional coupling of B. fragilis C10 protease genes with those for staphostatin-like inhibitors [9]. In the current study transcriptional coupling was also identified for the B. thetaiotaomicron btp and bti genes by Reverse Transcriptase PCR.…”

Prevalence and antimicrobial susceptibility of enterotoxigenic extra-intestinal Bacteroides fragilis among 13-year collection of isolates in Kuwait

“…This difference in the distribution of bft gene may be related to the severity of illness, prior antimicrobial therapy, type of the diet and thus gut flora and the method used to detect the enterotoxin. In addition, more than half (51.2%) of the isolates from bloodstream infections in Kuwait were enterotoxin producers which was much higher than previous reports from the USA and Japan (19)(20)(21)(22)(23)(24)(25)(26)(27)(28) et al, 1996, respectively) [16,28]. In our study, simultaneous harboring of 2, 3 and 4 bfp isotypes occurred in 71, 33 and 6 isolates, respectively, which is higher than those reported by Sarvari et al, and among the most bft-positive strains, bfp-1 was the most prevalent isotype.…”

“…This equates with 16.2% of the 210 bft-positive isolates. The sources of these resistant isolates were WIs [23], biopsy samples [4], BSI [3] and LRTIs [3]. A cfiA gene was detected in one B. fragilis strain that showed susceptibility to both imipenem and meropenem with MIC of 2 and 4 μg/ml, respectively.…”

Mobile genetic elements of the human gastrointestinal tract

“…Homologs of these genes were detected in both clinical isolates of B. fragilis and normal human fecal microbiota. 94 Another example is tetQ, a gene located on conjugative transposons of the Bacteroides species in the gut, but on an insertion sequence 21 (IS21) family transposon in the Prevotella species in the oral cavity. 95 This observation not only indicates HGT, but also different routes of dissemination of the same resistance gene by HGT in two locations of the GIT.…”