Analysis of bacterial detachment from substratum surfaces by the passage of air-liquid interfaces.
(73/843)
A theoretical analysis of the detachment of bacteria adhering to substratum surfaces upon the passage of an air-liquid interface is given, together with experimental results for bacterial detachment in the absence and presence of a conditioning film on different substratum surfaces. Bacteria (Streptococcus sobrinus HG1025, Streptococcus oralis J22, Actinomyces naeslundii T14V-J1, Bacteroides fragilis 793E, and Pseudomonas aeruginosa 974K) were first allowed to adhere to hydrophilic glass and hydrophobic dimethyldichlorosilane (DDS)-coated glass in a parallel-plate flow chamber until a density of 4 x 10(6) cells cm(-2) was reached. For S. sobrinus HG1025, S. oralis J22, and A. naeslundii T14V-J1, the conditioning film consisted of adsorbed salivary components, while for B. fragilis 793E and P. aeruginosa 974K, the film consisted of adsorbed human plasma components. Subsequently, air bubbles were passed through the flow chamber and the bacterial detachment percentages were measured. For some experimental conditions, like with P. aeruginosa 974K adhering to DDS-coated glass and an air bubble moving at high velocity (i.e., 13.6 mm s(-1)), no bacteria detached upon passage of an air-liquid interface, while for others, detachment percentages between 80 and 90% were observed. The detachment percentage increased when the velocity of the passing air bubble decreased, regardless of the bacterial strain and substratum surface hydrophobicity involved. However, the variation in percentages of detachment by a passing air bubble depended greatly upon the strain and substratum surface involved. At low air bubble velocities the hydrophobicity of the substratum had no influence on the detachment, but at high air bubble velocities all bacterial strains were more efficiently detached from hydrophilic glass substrata. Furthermore, the presence of a conditioning film could either inhibit or stimulate detachment. The shape of the bacterial cell played a major role in detachment at high air bubble velocities, and spherical strains (i.e., streptococci) detached more efficiently than rod-shaped organisms. The present results demonstrate that methodologies to study bacterial adhesion which include contact with a moving air-liquid interface (i.e., rinsing and dipping) yield detachment of an unpredictable number of adhering microorganisms. Hence, results of studies based on such methodologies should be referred as "bacterial retention" rather than "bacterial adhesion". (+info)
Polysaccharide biosynthesis locus required for virulence of Bacteroides fragilis.
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Bacteroides fragilis, though only a minor component of the human intestinal commensal flora, is the anaerobe most frequently isolated from intra-abdominal abscesses. B. fragilis 9343 expresses at least three capsular polysaccharides-polysaccharide A (PS A), PS B, and PS C. Purified PS A and PS B have been tested in animal models and are both able to induce the formation of intra-abdominal abscesses. Mutants unable to synthesize PS B or PS C still facilitate abscess formation at levels comparable to those of wild-type 9343. To determine the contribution of PS A to abscess formation in the context of the intact organism, the PS A biosynthesis region was cloned, sequenced, and deleted from 9343 to produce a PS A-negative mutant. Animal experiments demonstrate that the abscess-inducing capability of 9343 is severely attenuated when the organism cannot synthesize PS A, despite continued synthesis of the other capsular polysaccharides. The PS A of 9343 contains an unusual free amino sugar that is essential for abscess formation by this polymer. PCR analysis of the PS A biosynthesis loci of 50 B. fragilis isolates indicates that regions flanking each side of this locus are conserved in all strains. The downstream conserved region includes two terminal PS A biosynthesis genes that homology-based analyses predict are involved in the synthesis and transfer of the free amino sugar of PS A. Conservation of these genes suggests that this sugar is present in the PS A of all serotypes and may explain the abscessogenic nature of B. fragilis. (+info)
gyrA mutations associated with quinolone resistance in Bacteroides fragilis group strains.
(75/843)
Mutations in the gyrA gene contribute considerably to quinolone resistance in Escherichia coli. Mechanisms for quinolone resistance in anaerobic bacteria are less well studied. The Bacteroides fragilis group are the anaerobic organisms most frequently isolated from patients with bacteremia and intraabdominal infections. Forty-four clinafloxacin-resistant and-susceptible fecal and clinical isolates of the B. fragilis group (eight Bacteroides fragilis, three Bacteroides ovatus, five Bacteroides thetaiotaomicron, six Bacteroides uniformis, and 22 Bacteroides vulgatus) and six ATCC strains of the B. fragilis group were analyzed as follows: (i) determination of susceptibility to ciprofloxacin, levofloxacin, moxifloxacin, and clinafloxacin by the agar dilution method and (ii) sequencing of the gyrA quinolone resistance-determining region (QRDR) located between amino acid residues equivalent to Ala-67 through Gln-106 in E. coli. Amino acid substitutions were found at hotspots at positions 82 (n = 15) and 86 (n = 8). Strains with Ser82Leu substitutions (n = 13) were highly resistant to all quinolones tested. Mutations in other positions of gyrA were also frequently found in quinolone-resistant and -susceptible isolates. Eight clinical strains that lacked mutations in their QRDR were susceptible to at least two of the quinolones tested. Although newer quinolones have good antimicrobial activity against the B. fragilis group, quinolone resistance in B. fragilis strains can be readily selected in vivo. Mutational events in the QRDR of gyrA seem to contribute to quinolone resistance in Bacteroides species. (+info)
Susceptibility of the Bacteroides fragilis group to newer quinolones and other standard anti-anaerobic agents.
(76/843)
The susceptibilities of 200 clinical isolates of the Bacteroides fragilis group to four quinolones (moxifloxacin, clinafloxacin, trovafloxacin and ciprofloxacin) were determined, as well as to cefoxitin, clindamycin, metronidazole, imipenem and ticarcillin-clavulanic acid. The results for the latter five agents were compared with those of a study on 200 isolates done 6 years previously. Clinafloxacin and trovafloxacin were the most active agents tested with MIC90s lower than all other antimicrobials except imipenem. Susceptibility rates for imipenem, ticarcillin- clavulanic and metronidazole continue to be high, although resistant strains are emerging. For ticarcillin-clavulanic acid and metronidazole, MIC90s increased four- to eight-fold for the B. fragilis species between the two study periods. (+info)
In vitro activities of MK-0826 and 16 other antimicrobials against Bacteroides fragilis group strains.
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The activity of MK-0826, a new carbapenem, against 309 Bacteroides fragilis group strains was investigated and compared with that of 11 other beta-lactam and 5 non-beta-lactam agents. MK-0826 showed excellent activity (MICs ranged from < or =0.06 to 4 microg/ml). The new carbapenem may be useful in the treatment of mixed anaerobic infections involving B. fragilis group strains. (+info)
Structural rationale for the modulation of abscess formation by Staphylococcus aureus capsular polysaccharides.
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Staphylococcus aureus is a medically important bacterial pathogen that is a common cause of superficial and deep-seated abscesses in humans. Most S. aureus isolates produce either a serotype 5 or 8 capsular polysaccharide (CP) that has been shown to enhance bacterial virulence. We investigated the role of S. aureus CPs in modulating abscess formation in an experimental animal model of intraabdominal infection. Structural studies of CP8 revealed that it has a zwitterionic charge motif conferred by the negatively charged carboxyl group of N-acetylmannosaminuronic acid and free amino groups available on partially N-acetylated fucosamine residues. We report that purified CP5 and CP8 facilitated intraabdominal abscess formation in animals when given i.p. with a sterile cecal contents adjuvant. Chemical modifications that neutralized the positively or negatively charged groups on CP8 abrogated its ability to provoke abscesses. Rats prophylactically treated with CP8 s.c. were protected against abscess formation induced by homologous or heterologous zwitterionic polysaccharides. Likewise, treatment with CP8 protected against challenge with viable S. aureus strains PS80 (a capsule type 8 strain) or COL (a methicillin-resistant capsule type 5 strain). Purified CP8 was a potent activator of rat and human CD4(+) T cells in vitro. When transferred to naive rats, these activated T cells modulated the development of intraabdominal abscess formation. These results provide a structure/function rationale for abscess formation by S. aureus and expand the sphere of encapsulated organisms that interact directly with T cells to regulate this host response to bacterial infection. (+info)
Escherichia coli hemoglobin protease autotransporter contributes to synergistic abscess formation and heme-dependent growth of Bacteroides fragilis.
(79/843)
Intra-abdominal infections (IAI) continue to be a serious clinical problem. Bacterial synergism is an important factor that influences the shift from contamination to IAI, leading to the development of lesions and abscess formation. Escherichia coli and Bacteroides fragilis are particularly abundant in IAI. The underlying molecular mechanisms of this pathogenic synergy are still unclear. The role of the hemoglobin protease (Hbp) autotransporter protein from E. coli in the synergy of IAI was investigated. Hbp is identical to Tsh, a temperature-sensitive hemagglutinin associated with avian pathogenic E. coli. Clinical isolates from miscellaneous extraintestinal infections were phenotypically and genotypically screened for Hbp. The presence of Hbp was significantly associated with E. coli isolated from IAI and other extraintestinal infections. In a murine infection model, Hbp was shown to contribute to the pathogenic synergy of abscess development. Mice immunized with Hbp were protected against mixed infections and did not develop abscess lesions. Furthermore, an E. coli wild-type strain that did not induce abscess formation in the synergy model was transformed with a plasmid encoding the hbp gene, and mixed infections with this strain lead to increased growth of B. fragilis and induction of abscess lesions. Growth-promoting studies showed that purified Hbp is able to deliver heme to B. fragilis strain BE1. In conclusion, results suggest the synergy of abscess formation by E. coli and B. fragilis can be partly explained by the capacity of B. fragilis to intercept Hbp and iron from heme to overcome the iron restrictions imposed by the host. (+info)
Pharmacodynamics of trovafloxacin and levofloxacin against Bacteroides fragilis in an in vitro pharmacodynamic model.
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An in vitro pharmacodynamic investigation was conducted to explore whether the area under the concentration time curve from 0 to 24 h (AUC(0-24))/MIC ratio could predict fluoroquinolone performance against Bacteroides fragilis. An in vitro model was used to generate kill curves for trovafloxacin (TVA) and levofloxacin (LVX) at AUC(0-24)/MIC ratios of 1 to 406 against three strains of B. fragilis (ATCC 25285, ATCC 23745, and clinical isolate M97-117). TVA and LVX were bolused prior to the start of experiments to achieve the corresponding AUC(0-24)/MIC ratio. Experiments were performed in duplicate over 24 h and in an anaerobic environment. Analyses of antimicrobial performance were conducted by comparing the rates of bacterial kill (K) using nonlinear regression analysis with 95% confidence intervals. Statistical significance was defined as a lack of overlap in the 95% confidence limits generated from the slope of each kill curve. For both TVA and LVX, K was maximized once an AUC(0-24)/MIC ratio of > or =40 was achieved and was not further increased despite a 10-fold increase in AUC(0-24)/MIC from approximately 40 to 400 against all three strains of B. fragilis. No significant differences were found in K between AUC(0-24)/MIC ratios of approximately 40 to 200. In experiments where AUC(0-24)/MIC ratios that were > or = 5 and < or = 44 were conducted, 64% demonstrated regrowth at 24 h. Resistant strains were selected in 50% of those experiments, demonstrating regrowth, which resulted in increased MICs of two- to 16-fold for both TVA and LVX. Regrowth did not occur, nor were resistant strains selected in any studies with an AUC/MIC that was > 44. Our findings suggest that fluoroquinolones provide antibacterial effects against B. fragilis in a concentration-independent manner associated with an AUC(0-24)/MIC ratio of > or =40. Also, the potential for the selection of resistant strains of B. fragilis may increase with an AUC(0-24)/MIC ratio of < or =44. (+info)