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PubMed1994

The treatment of irradiated mice with polymicrobial infection caused by Bacteroides fragilis and Escherichia coli.

The effects on the faecal flora and the efficacies of various antibiotic regimens administered as treatment for a mixed infection caused by Bacteroides fragilis and Escherichia coli in the irradiated host were investigated in a subcutaneous abscess model with C3H/HeN mice which had been exposed to 60Co. The regimens used included imipenem, ofloxacin, metronidazole and the combination of ofloxacin and metronidazole. The incidence of mortality associated with each regimen was as follows: 2 of 20 (10%) mice treated with ofloxacin; 16 of 20 (80%) given metronidazole (P < 0.05 compared with ofloxacin); 8 of 20 (40%) given imipenem (P < 0.05 compared with ofloxacin); 5 of 20 (25%) given the combination of ofloxacin and metronidazole (P = NS compared with ofloxacin); and 15 of 20 (75%) controls given a placebo (P < 0.05 compared with ofloxacin). Compared with the control group, the mean number of lactose-fermenting facultative anaerobes in the faeces of irradiated mice decreased significantly during treatment with either ofloxacin or ofloxacin combined with metronidazole; rose significantly from day 6 during treatment with metronidazole and was similar during treatment with imipenem. The numbers of strict anaerobes fell with all regimens (including the placebo) but, compared with the control group, were significantly higher in the ofloxacin and imipenem groups and significantly lower in the groups which received metronidazole (with or without ofloxacin). Imipenem and the combination of ofloxacin and metronidazole led to significant reductions in the numbers of cfu of both E. coli and B. fragilis in the abscesses compared with the placebo; ofloxacin alone caused a reduction in the number of cfu of E. coli only and metronidazole alone caused a reduction in the number of cfu of B. fragilis only. While the administration of metronidazole had a favourable effect on the B. fragilis component of the localized infection, there was a higher incidence of mortality with this agent, probably because it led to an increase in the number of Enterobacteriaceae in the faeces at the expense of a reduction in the number of strict anaerobes. Antimicrobial agents such as imipenem or the combination of a quinolone, such as ofloxacin, and metronidazole may be used successfully to treat localized infections in the irradiated host while avoiding potentially deleterious increases in the number of facultative anaerobes in the bowel.

Abscess↗
PubMed2003

The complex oxidative stress response of Bacteroides fragilis: the role of OxyR in control of gene expression.

Gram-negative anaerobes in the genus Bacteroides are the predominant members of the GI-tract microflora where they play an important role in normal intestinal physiology. Bacteroides spp. also are significant opportunistic pathogens responsible for an array of intra-abdominal and other infections. Bacteroides fragilis is the most common anaerobic pathogen and it possesses virulence factors such as a capsule and neuraminidase that contribute to its success as a pathogen. Infection occurs when organisms escape from the anaerobic colon to aerobic sites such as the peritoneum where O(2) concentrations average 6%. Thus in addition to the classic virulence factors, resistance to oxidative stress is essential and may be involved in the initiation and persistence of infection. In fact, B. fragilis is highly O(2) tolerant, surviving extended periods (>24h) of O(2) exposure without a significant affect on viability. For protection against this oxidative stress B. fragilis mounts a complex physiological response that includes induction of >28 proteins involved in detoxification of oxygen radicals, protection of macromolecules, and adaptive physiology. One experimental strategy used to characterize this oxidative stress response is the direct detection of genes and proteins induced during exposure to O(2) or H(2)O(2). The methods employed have included RNA differential display to capture unique mRNA transcripts produced during oxidative stress, and native or 2D-gel electrophoresis to isolate and identify newly formed stress-induced proteins. Using these and other approaches a wide array of genes induced by oxidative stress have been discovered. These include genes for catalase, superoxide dismutase, thioredoxin-peroxidase, p20-peroxidase, cytochrome c peroxidase, Dps, alkyl hydroperoxidase, aerobic ribonucleotide reductase, ruberythrin, starch utilization, aspartate decarboxylase, and an RNA binding protein. The genes encoding these activities fall into three regulatory classes: (1) induced by O(2) only, (2) induced by H(2)O(2) only, and (3) induced by either O(2) or H(2)O(2). Such a complex regulatory response will likely involve multiple regulators. Thus far one regulator has been identified, OxyR, which controls a subset of the class 3 genes that are induced by either O(2) or H(2)O(2). OxyR responds rapidly to oxidative stress and transcriptional analyses have shown that OxyR-controlled genes are activated by as little as 0.5% O(2) or 10 microM H(2)O(2). Maximal expression of most OxyR regulon genes was reached at 50 microM H(2)O(2) and 2% O(2). These oxidant concentrations are similar to environmental levels that would be experienced by the organisms in tissues outside of the colon suggesting that the OxyR regulon would be induced during the course of an infection.

Journal Article↗
PubMed1982

Characterization of opsonins for Bacteroides fragilis in immune sera collected from experimentally infected mice.

Serum collected from mice experimentally infected with Bacteroides fragilis 23745 (immune serum) was analyzed for its ability to opsonize the in vitro ingestion of this organism by mouse peritoneal macrophages. B. fragilis was shown to be phagocytized most efficiently in the presence of immune serum although normal mouse serum demonstrated reduced, but significant, opsonic activity. Phagocytosis was greater in the presence of serum collected from animals inoculated twice with the organism than in the presence of serum from once-inoculated animals. The increased opsonic activity of serum from twice-inoculated animals compared to singly inoculated animals was associated with increases in immunoglobulin G1(IgG1), IgG2a, and IgG2b but not IgM. Adsorption analysis of immune serum with homologous or heterologous bacterial antigens indicated that both antibody and complement act synergistically in opsonizing B. fragilis, although either alone may effectively opsonize this organism. Further evaluation of antibody-mediated opsonization revealed that prior treatment of heat-inactivated immune serum with the reducing agent 2-mercaptoethanol caused a slight, but significant, decrease in opsonic activity, thus indicating that IgM is a minor opsonizing antibody for B. fragilis. When ingestion of a B. fragilis stock strain (23745) was compared to a recent clinical isolate (C-1), it was observed that the stock strain was more easily phagocytized in the presence of normal mouse serum, thus suggesting a possible anti-opsonic-phagocytic property of the clinical strain. In addition, the clinical isolate was phagocytized to a significantly greater degree in an aerobic than an anaerobic environment. Subsequent analysis of in vitro killing of B. fragilis 23745 by peritoneal macrophages reflected the previous results in that optimal killing occurred in the presence of immune serum, although normal serum promoted phagocytic killing to an intermediate degree. Thus, these studies implicate both antibody and complement, either alone or in combination, in the opsonization of B. fragilis. Moreover, the virulence of clinical B. fragilis strains may relate to their refractoriness to opsonization and phagocytosis.

Animals↗
PubMed1982

Detection of species-specific and cross-reactive cell-surface antigens of Bacteroides species by an indirect enzyme-linked immunosorbent assay.

EDTA-released outer-membrane antigen complexes were prepared from 172 laboratory and reference strains and 43 fresh clinical or faecal isolates representing 20 species or subspecies of Bacteroides, together with 13 species of other genera. These antigens were titrated against antisera to whole, live cells of 21 species or subspecies of Bacteroidaceae in an indirect enzyme-linked immunosorbent assay (ELISA). The presence of species-specific antigens was investigated and cross reactions between species were noted. Results showed that a high proportion of the species possess species-specific antigens with little significant cross reactivity. We believe that the ELISA system described here detects antigens that represent the whole cell surface of bacteroides organisms. We have exploited the sensitivity of the system and its quantitative potential to define approaches for those wishing to use serological approaches for either the identification of Bacteroides species or for the titration of serum antibodies in patients with a possible bacteroides infection.

Antigens, Bacterial↗
PubMed1986

Interactions between polymorphonuclear leucocytes, Bacteroides sp, and Escherichia coli: their role in the pathogenesis of mixed infection.

Five Bacteroides fragilis strains and five Bacteroides vulgatus strains were compared with regard to their ability to consume complement and to fix C3, their killing by polymorphonuclear leucocytes, and their ability to inhibit the bactericidal effect of serum and polymorphs on Escherichia coli strains. Complement consumption was positively related to C3 fixation, but no relation was observed between these variables and the killing of the anaerobes. Greatest inhibition of the killing of E coli by serum and polymorphs was achieved with the bacteroides strains that fixed most complement. The greater virulence of B fragilis in mixed infections with E coli was not reflected either by a greater ability to inhibit the killing of E coli or a greater resistance of the anaerobes themselves to the bactericidal effect of serum and polymorphs.

Animals↗
PubMed1992

Epidemiological aspects of infections caused by Bacteroides fragilis and Clostridium difficile.

Bacteroides fragilis and Clostridium difficile are two of the most common anaerobes associated with human disease. Studies on the epidemiology of Bacteroides fragilis are limited and are based predominantly on serogrouping, which suggests intraspecies differences. Further studies using newer techniques for typing are required to elucidate the epidemiological characteristics of this important pathogen. By contrast, numerous phenotypic, immunological and molecular methods have been developed for typing and fingerprinting of Clostridium difficile and applied in epidemiological studies to show conclusively that Clostridium difficile is nosocomially acquired and that there is transmission and cross-infection between hospital patients.

Animals↗
PubMed1975

In vivo protection of Fusobacterium necrophorum from penicillin by Bacteroides fragilis.

A mixed infection of Bacteroides fragilis and Fusobacterium necrophorum was resistant to treatment with penicillin even though a pure F. necrophorum infection could be successfully treated with penicillin. Since B. fragilis alone did not produce infection, these results indicate that B. fragilis can protect F. necrophorum from penicillin in vivo. The extent of protection afforded by a strain of B. fragilis was related to its level of resistance to penicillin. Only a few cells of B. fragilis were required in the initial bacterial injection. Moreover, protection was demonstrated when B. fragilis cells were injected as late as 24 h after the F. necrophorum cells. Protection of F. necrophorum from penicillin by B. fragilis was also demonstrated in vitro.

Animals↗
PubMed1984

Presence of two unique genes encoding macrolide-lincosamide-streptogramin resistance in members of the Bacteroides fragilis group as determined by DNA-DNA homology.

The relationship of a previously described, plasmid-encoded macrolide-lincosamide-streptogramin (MLS) resistance determinant to Bacteroides fragilis group clinical isolates from 11 different patients with bacteroides infections was assessed using in situ hybridization. Most of the strains were found to have DNA sequences homologous with the bacteroides MLS plasmid, pBF4, but this homology was exclusively to chromosomal DNA. Two organisms isolated from different sites in a single patient did not share homology with the plasmid, and probably represent a second type of MLS gene. The MLS resistance plasmids, pBF4 (from Bact. fragilis) and pE194 (from Staphylococcus aureus), did not share homologous sequences; therefore at least one of the bacteroids MLS genes is different from that found in Gram-positive organisms.

Bacteroides fragilis↗
PubMed1983

Are first-generation cephalosporins effective for antibiotic prophylaxis in elective surgery of the colon?

First-generation cephalosporins have recently declined in popularity as antibiotics for prophylaxis in elective surgery of the colon, but their efficacy has not been defined precisely. In a prospective randomized study, 44 patients who underwent elective colonic operations received, preoperatively, cefazolin in a parenteral dose adequate to kill aerobic coliforms. Six had wound infections; Bacteroides fragilis was grown, along with other organisms, from all these wounds. In contrast, only 1 of 57 similar patients had a wound infection after receiving, preoperatively, erythromycin base and metronidazole orally--directed at anaerobic bacteria. Local contamination, predominantly by anaerobic bacteria, is the main cause of wound infection after elective surgery of the colon. Even in what seems to be adequate dosage, first-generation cephalosporins are not antibiotics of first choice for preventing wound infections after these operations.

Aged↗
PubMed2006

Prevalence of enterotoxigenic Bacteroides fragilis in hospital-acquired diarrhea.

Stool specimens from 152 hospitalized patients with diarrhea were analyzed for the presence of enterotoxigenic Bacteroides fragilis (ETBF) by a nested polymerase chain reaction (PCR) assay. ETBF gene sequences were directly detected in 14/152 (9.21%) stools of patients. The prevalence of ETBF in hospital-acquired diarrhea was statistically significant when compared to a prevalence of 2.3% in control subjects (P = 0.04). B. fragilis was cultured from 19.7% (30/152) patients with diarrhea; 4 of these isolates were enterotoxigenic. To determine whether colonization with B. fragilis is heterogeneous in nature, multiple colonies from 17 individual patients were analyzed for enterotoxin gene sequences and genotyped by arbitrarily primed PCR. Of these 17 patients, 13 harbored multiple strain types suggesting heterogeneity of colonization with both enterotoxigenic and non-enterotoxigenic strains. Identification of ETBF in the stools of 10 patients in the absence of a positive culture is likely due to the noted heterogeneity and suggests that detection of enterotoxin by PCR should be performed directly in the stool. These preliminary data indicate that ETBF may play a role in hospital-acquired diarrhea of unknown origin and suggest the need for further studies.

Bacteroides Infections↗
PubMed1989

Pathogenicity of enterococci in a rat model of fecal peritonitis.

The pathogenicity of enterococci in intraabdominal sepsis has not been clarified. Therefore, fecal-type peritonitis was induced in rats by intraperitoneal injection of barium sulfate along with a bacterial inoculum consisting of Escherichia coli, Bacteroides fragilis, and Clostridium perfringens with or without Streptococcus faecalis. Mortality at 19 d and characteristics of intraabdominal abscesses in survivors at 19 d were analyzed. The presence of S. faecalis in the original inoculum was significantly associated with death or large (greater than 20 mm) abscess formation when these two end points were examined together. S. faecalis may synergize with other bacteria in intraabdominal sepsis to augment morbidity and possibly mortality.

Abscess↗