Clinical Isolates Of Bacteroides Research Articles

Increasing Trends in Antimicrobial Resistance among Clinically Important Anaerobes and Bacteroides fragilis Isolates Causing Nosocomial Infections: Emerging Resistance to Carbapenems

This study reports data on the susceptibilities to five commonly used antianaerobic agents of five clinically frequently encountered anaerobes from 2000 to 2007 and to Bacteroides fragilis isolates causing nosocomial infections from 1990 to 2006. There was a trend of decreasing susceptibilities of these anaerobes to ampicillin-sulbactam, cefmetazole, chloramphenicol, and clindamycin with time during the study period. The rates of susceptibility to clindamycin and cefmetazole for all clinical isolates of Bacteroides fragilis isolates were higher than those of isolates associated with nosocomial infections. The MICs of 207 anaerobic blood isolates collected in 2006 to 14 antimicrobial agents were determined by the agar dilution method. The rates of nonsusceptibility to imipenem and meropenem were 7% and 12% for B. fragilis isolates (n = 60), 7% and 3% for Bacteroides thetaiotamicron isolates (n = 30), 4% and 4% for Fusobacterium species (n = 27), 6% and 0% for Prevotella species (n = 16), 15% and 0% for Clostridium species (n = 28), and 0% and 0% for Peptostreptococcus species (n = 32). The rates of susceptibility to moxifloxacin were 90% for B. fragilis isolates, 87% for B. thetaiotaomicron isolates, 81% for Fusobacterium species, 75% for Prevotella species, 93% for Clostridium species, and 78% for Peptostreptococcus species. Thirty-six percent of Clostridium species and 12% of Peptostreptococcus species were not susceptible to metronidazole. Comparison of the data with the data from a previous survey from the same institute in 2002 revealed higher rates of nonsusceptibility to carbapenems, especially for B. fragilis, Fusobacterium species, and Prevotella species isolates. The high rates of nonsusceptibility to commonly used antianaerobic agents mandate our attention, and periodic monitoring of the trend of the resistance is crucial.

Prevalence and degree of expression of the carbapenemase gene (cfiA) among clinical isolates of Bacteroides fragilis in Nottingham, UK.

The carbapenemase gene (cfiA) was detected in 12 (6.9%) out of 175 clinical isolates of Bacteroides fragilis from Nottingham, three times the frequency reported from France. Only one gene copy was present in all cases. Eleven (6.3%) of the cfiA-positive isolates were susceptible to imipenem or meropenem (MIC < 8 mg/L); strains of this type have the potential to convert to high-level resistance. One isolate (0.6%) displayed resistance to both carbapenem antibiotics and was associated with specific carbapenemase activity six times that of the sensitive isolates.

Distinctive Outer Membrane Protein and Lipopolysaccharide Composition ofBacteroides fragilisStrains that Produce Metallo-β-lactamase

The outer membrane protein and lipopolysaccharide compositions ofBacteroides fragilisstrains which produced metallo-β-lactamase were shown to be different from those of fully sensitive random clinical isolates ofBacteroides fragilisin which metallo-β-lactamase production was not detected. This may reflect differences in the permeability barrier and provides phenotypic evidence thatBacteroides fragiliswhich produce metallo-β-lactamase may belong to a separate biotype. Outer membrane profiles may provide a rapid means of identifying these problem strains.

Analysis of trends in antimicrobial resistance patterns among clinical isolates of Bacteroides fragilis group species from 1990 to 1994.

Antimicrobial resistance, including plasmid-mediated resistance, among Bacteroides fragilis group species is well documented. A 5-year (1990-1994) prospective, eight-center survey of 3,177 clinical isolates of Bacteroides species was undertaken to review trends in resistance, using the breakpoints for full and intermediate susceptibility established by the National Committee for Clinical Laboratory Standards. No documented resistance to either metronidazole or chloramphenicol was found in this survey. Among B. fragilis isolates virtually no resistance was seen to imipenem, meropenem, ampicillin/sulbactam, piperacillin/tazobactam, or ticarcillin/clavulanate. Significant increases in resistance among B. fragilis isolates to cefotetan, ceftizoxime, and clindamycin (p < .01) were noted. Resistance to cefoxitin remained unchanged. Among the non-fragilis species of the B. fragilis group, there was virtually no resistance to imipenem, meropenem, chloramphenicol, or metronidazole. The three beta-lactamase inhibitors had increasing levels of resistance, although 95%-98% of strains were susceptible (p < .05). There was a significant decline in cefoxitin, cefmetazole, and clindamycin activity over time against these strains (p <.01). There was a significant (P < .001) increase in geometric mean minimum inhibitory concentration for most drugs and species tested from 1990 to 1994. Clusters in the eight institutions could not account for this rise in resistance. This survey demonstrates that rates of resistance of B. fragilis and non-fragilis species of B. fragilis group are increasing.

Comparative In Vitro Activity of Cefoxitin vs. Cefotetan Against Clinical Isolates of Bacteroides and Prevotella Species

Comparative In Vitro Activity of Cefoxitin vs. Cefotetan Against Clinical Isolates of Bacteroides and Prevotella Species

Neuraminidase production byBacteroidesspecies

128 strains of Bacteroides isolated from clinical specimens were surveyed for their ability to produce neuraminidase. All strains of Bacteroides fragilis and the B. fragilis group were neuraminidase-positive, as were strains of B. oralis and B. bivius. All strains of B. capillosus, B. ruminicola, B. disiens, B. multiacidus and B. uniformis did not produce a detectable neuraminidase. When human erythrocytes were exposed to cell extracts of neuraminidase-producing Bacteroides, and then tested with peanut (Arachis hypogeae) lectin, agglutination occurred. It was concluded that the production of neuraminidase by clinical isolates of Bacteroides may be associated with the pathophysiology of severe Bacteroides infections.

Neuraminidase production by Bacteroides species

128 strains of Bacteroides isolated from clinical specimens were surveyed for their ability to produce neuraminidase. All strains of Bacteroides fragilis and the B. fragilis group were neuraminidase-positive, as were strains of B. oralis and B. bivius. All strains of B. capillosus, B. ruminicola, B. disiens, B. multiacidus and B. uniformis did not produce a detectable neuraminidase. When human erythrocytes were exposed to cell extracts of neuraminidase-producing Bacteroides, and then tested with peanut (Arachis hypogeae) lectin, agglutination occurred. It was concluded that the production of neuraminidase by clinical isolates of Bacteroides may be associated with the pathophysiology of severe Bacteroides infections.

Penicillin resistance and penicillinase production in clinical isolates of Bacteroides melaninogenicus.

The minimum inhibitory concentrations (MIC) of penicillin and six other antimicrobials were determined for 50 clinical isolates of Bacteroides melaninogenicus. Agar dilution susceptibilities were performed using supplemented brucella blood agar and the proposed National Committee for Clinical Laboratory Standards standard method for anaerobes; results with the two methods were comparable. A penicillin concentration >/=0.8 mug/ml was needed to inhibit 56% of the isolates, whereas 100% were susceptible to 0.1 mug of clindamycin per ml. All isolates with penicillin MIC values >/=0.8 mug/ml produced beta-lactamase using a slide method. A micro-iodometric assay was used to quantitate beta-lactamase production in six isolates. The beta-lactamase activity of B. melaninogenicus was comparable to that of a Staphylococcus aureus isolate but was not inducible, and the specific amount produced correlated only partially with penicillin MIC values. A clinical review of patients from whom the beta-lactamase-producing strains of B. melaninogenicus were isolated did not suggest any increased virulence in these strains or an unexpectedly poor clinical response to appropriate therapy.

Comparison of the In Vitro Bactericidal Activity of Human Serum and Leukocytes Against Bacteroides fragilis and Fusobacterium mortiferum in Aerobic and Anaerobic Environments

In aerobic and anaerobic in vitro environments, Fusobacterium mortiferum was killed by human leukocytes or serum alone or in combination; clinical isolates of Bacteroides fragilis were killed only by leukocytes in the presence of serum.

Isolation of plasmid deoxyribonucleic acid from two strains of Bacteroides.

Two clinical isolates of Bacteroides contained covalently closed circular deoxyribonucleic acid (DNA) as shown by sedimentation in an alkaline sucrose gradient, CsCl ethidium bromide equilibrium centrifugation, and electron microscopy. Bacteriodes fragilis N1175 contained a homogeneous species of plasmid DNA with a molecular weight of 25 x 10(6). Bacteroides ochraceus 2228 contained two distinct, covalently closed circular DNA elements. The larger cosedimented with the covalently closed circular DNA form of the R plasmid, R100, corresponding to a molecular weight of 70 x 10(6); the smaller sedimented as a 58S molecule with a calculated molecular weight of 25 x 10(6). The roles of these plasmids are unknown. Neither strain transferred antibiotic resistance to plasmid-negative Bacteroides or Escherichia coli, and neither produced bacteriocins active against other Bacteroides or sensitive indicator strains of E. coli.