Strain differentiation in Bacteroides fragilis by RAPD and Dendron computer-assisted gel analysis

Bacteroides fragilis induce necrosis on mice peritoneal macrophages: In vitro and in vivo assays

Bacteroides fragilis is an anaerobic bacteria component of human intestinal microbiota and agent of infections. In the host B. fragilis interacts with macrophages, which produces toxic radicals like NO. The interaction of activated mice peritoneal macrophages with four strains of B. fragilis was evaluated on this study. Previously was shown that such strains could cause metabolic and morphologic alterations related to macrophage death. In this work propidium iodide staining showed the strains inducing macrophage necrosis in that the labeling was evident. Besides nitroblue tetrazolium test showed that B. fragilis stimulates macrophage to produce oxygen radicals. In vivo assays performed in BalbC mice have results similar to those for in vitro tests as well as scanning electron microscopy, which showed the same surface pore-like structures observed in vitro before. The results revealed that B. fragilis strains studied lead to macrophage death by a process similar to necrosis.

bft gene subtyping in enterotoxigenic Bacteroides fragilis isolated from children with acute diarrhea

Enterotoxigenic Bacteroides fragilis (ETBF) strains are associated with diarrhea disease in farm animals and young children. In this study, the bft gene subtyping from ETBF strains recovered from one immunodeficient and two immunocompetent children with diarrhea were determined. Thirteen ETBF strains were isolated and by using a multiplex-PCR their bft subtypes were determined. All 13 ETBF strains harbored the bft-1 subtype and by AP-PCR they were clustered in the same group I. This study shows that ETBF strains can be present in acute diarrhea and that bft-1 subtype is often present in these organisms. However, further studies are needed to evaluate the role of this bft-1 subtype in the pathogenesis of diarrhea.

Bacteroides species produce Vibrio harveyi autoinducer 2-related molecules

Quorum sensing is a density-dependent gene regulation mechanism that has been described in many bacterial species in the last decades. Bacteria that use quorum sensing as part of their gene regulation circuits produce molecules called autoinducers that accumulate in the environment and activate target genes in a quorum-dependent way. Some specific clues led us to hypothesize that Bacteroides species can produce autoinducers and possess a quorum sensing system. First, Bacteroides are anaerobic bacteria that are frequently involved in polymicrobial infections. These infections often involve Pseudomonas aeruginosa and Staphylococcus aureus, two of the best understood examples of bacteria that employ quorum sensing systems as part of their pathogenesis. Also, studies have detected the presence of a quorum sensing gene involved in the production of autoinducers in Porphyromonas gingivalis, a species closely related to the Bacteroides genus. These and other evidences prompted us to investigate if Bacteroides strains could produce autoinducer molecules that could be detected by a Vibrio harveyi reporter system. In this paper, we show that supernatants of B. fragilis, B. vulgatus and B. distasonis strains are able to stimulate the V. harveyi quorum sensing system 2. Also, we were able to demonstrate that the stimulation detected is due to the production of autoinducer molecules and not the growth of reporter strains after addition of supernatant. Moreover, the phenomenon observed does not seem to represent the degradation of repressors possibly present in the culture medium used. We could also amplify bands from some of the strains tested using primers designed to the luxS gene of Escherichia coli. Altogether, our results show that B. fragilis, B. vulgatus and B. distasonis (but possibly some other species) can produce V. harveyi autoinducer 2-related molecules. However, the role of such molecules in the biology of these organisms remains unknown.

Bacteroides fragilis interferes with iNOS activity and leads to pore formation in macrophage surface

Bacteroides fragilis is the anaerobe most commonly recoverable from clinical specimens. The wide genetic diversity of this bacterium related with virulence potential is still an open question. In this study, we analyzed the morphological aspects and microbicide action of MØ during interactions with B. fragilis. A filamentous cytoplasm content release and a different actin organization colocalized with iNOS were detected. It was also possible to observe the reduction of NO production in the same conditions. The scanning electron microscopy showed the formation of pore-like structures in the surface of macrophages in the bacterial presence and by transmission electron microscopy we could observe the extrusion of cytoplasm contents as well as the condensation of chromatin in the nucleus periphery. These data suggest the existence of an inhibitory mechanism developed by B. fragilis strains for one of the macrophage microbicide actions.

Genetic diversity of Leptotrichia and description of Leptotrichia goodfellowii sp. nov., Leptotrichia hofstadii sp. nov., Leptotrichia shahii sp. nov. and Leptotrichia wadei sp. nov

Sixty strains of Gram-negative, anaerobic, rod-shaped bacteria from human sources initially assigned to Leptotrichia buccalis (n=58) and 'Leptotrichia pseudobuccalis' (n=2) have been subjected to polyphasic taxonomy. Full-length 16S rDNA sequencing, DNA-DNA hybridization, RAPD, SDS-PAGE of whole-cell proteins, cellular fatty acid analysis and enzymic/biochemical tests supported the establishment of four novel Leptotrichia species from this collection, Leptotrichia goodfellowii sp. nov. (type strain LB 57(T)=CCUG 32286(T)=CIP 107915(T)), Leptotrichia hofstadii sp. nov. (type strain LB 23(T)=CCUG 47504(T)=CIP 107917(T)), Leptotrichia shahii sp. nov. (type strain LB 37(T)=CCUG 47503(T)=CIP 107916(T)) and Leptotrichia wadei sp. nov. (type strain LB 16(T)=CCUG 47505(T)=CIP 107918(T)). Light and electron microscopy showed that the four novel species were Gram-negative, non-spore-forming and non-motile rods. L. goodfellowii produced arginine dihydrolase, beta-galactosidase, N-acetyl-beta-glucosaminidase, arginine arylamidase, leucine arylamidase and histidine arylamidase. L. shahii produced alpha-arabinosidase. L. buccalis and L. goodfellowii fermented mannose and were beta-galactosidase-6-phosphate positive. L. goodfellowii, L. hofstadii and L. wadei were beta-haemolytic. L. buccalis fermented raffinose. With L. buccalis, L. goodfellowii showed 3.8-5.5 % DNA-DNA relatedness, L. shahii showed 24.5-34.1 % relatedness, L. hofstadii showed 27.3-36.3 % relatedness and L. wadei showed 24.1-35.9 % relatedness. 16S rDNA sequencing demonstrated that L. hofstadii, L. shahii, L. wadei and L. goodfellowii each formed individual clusters with 97, 96, 94 and 92 % similarity, respectively, to L. buccalis.