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Biomedical subjects

F Namavar

Publications and source records attributed to F Namavar.

At least 37 records · Page 2Linked to original sources
PubMed1993

Establishing an experimental infection model for peritoneal dialysis: effect of inoculum and volume.

The effect of the number of bacteria and the volume of the inoculum was studied in an experimental infection model to establish a peritoneal dialysis model in the rat. Staphylococcus aureus was used in all experiments, and Staphylococcus epidermidis only in the volume experiments. A bacterial number between 10(8) and 10(9) colony-forming units (cfu) resulted in a time-dependent decrease of bacteria collected from the peritoneal cavity. Higher concentrations resulted in the death of animals, while lower concentrations were rapidly cleared. There was a positive correlation between the volume in which 3 x 10(8) cfu were dissolved and the number of bacteria isolated from the peritoneal cavity 24 hours after infection. The results of this study led to an experimental dialysis model using 10 mL of dialysis fluid and 0.5 mL of a suspension containing 3 x 10(8) cfu of Staphylococcus aureus.

Animals↗
PubMed1992

Effect of glucose concentration and dwell time of dialysis fluid on the antibacterial defense in the peritoneal cavity of rats.

To study the influence of dialysis fluid on the antibacterial defense in the peritoneal cavity of rats, especially glucose concentration and dwell time, an experimental infection was developed. Rats were injected intraperitoneally with dialysis fluid with a glucose concentration of 1.36%, 2.27%, or 3.86% or physiological saline. Subsequently 1, 4 or 18 hr thereafter an inoculum of approximately 3 x 10(8) colony forming units of Staphylococcus aureus was administered intraperitoneally (i.p.) Next, 24 hr after the inoculation the number of viable bacteria was determined. Peritoneal cells (PC) isolated 1, 4 and 18 hr after the administration of dialysis fluid were tested for their capacity to kill S. aureus in vitro. A positive relation was observed between the glucose concentration and the number of bacteria isolated; the longer the dwell time the lower this number. In vitro PC isolated at the various intervals did not differ in their capacity to kill S. aureus. It is concluded that the glucose concentration in dialysis fluid impairs the antistaphylococcal defense in the peritoneal cavity of rats. A relatively long dwell time enhances this defense. These results cannot be explained by a lower capacity of the PC to kill S. aureus in vitro.

Animals↗
PubMed1991

A nosocomial outbreak of amoxycillin-resistant non-typable Haemophilus influenzae in a respiratory ward.

A nosocomial outbreak of acute bronchitis due to amoxycillin-resistant, non-typable Haemophilus influenzae occurred in a 23-bed unit, housing patients with respiratory disorders. Within a period of one month, 13 patients and two, previously healthy, members of staff were affected. The isolates were studied for strain relatedness by serotyping, biotyping and major outer membrane protein (MOMP) profiles after SDS-polyacrylamide gel electrophoresis; 13 of the isolates belonged to the same biotype and MOMP type, indicating cross-infection. Routine throat cultures of all patients and personnel were undertaken. To stop the epidemic, patients and nurses positive for amoxycillin-resistant H. influenzae were isolated or sent home and, if symptomatic, were treated with co-trimoxazole. We stress the importance of early intervention when amoxycillin-resistant H. influenzae strains occur in a ward.

Acute Disease↗
PubMed1991

A study of the candidate virulence factors of Bacteroides fragilis.

Bacteroides fragilis strains were classified as virulent or avirulent on the basis of their clearance from the subcutaneous tissues of mice. To determine the factors which may contribute to the virulence of B. fragilis strains, we studied encapsulation, hydrophobicity, growth rate, serum sensitivity, agglutination with erythrocytes of different origin, and neuraminidase production. The strains of the virulent group displayed a higher growth rate in broth and a lower sensitivity to the bactericidal activity of serum than the strains of the avirulent group. They also agglutinated different types of erythrocytes more strongly than did the avirulent strains. No significant differences were found between the two groups of strains as regards encapsulation, hydrophobicity and neuraminidase activity.

Animals↗
PubMed1991

Early events after intra-abdominal infection with Bacteroides fragilis and Escherichia coli.

Growth of Bacteroides fragilis and Escherichia coli was monitored during early stages of single (mono-) and mixed intra-abdominal infection in a rat fibrin clot model. When B. fragilis and E. coli were together involved in the infection, B. fragilis numbers increased about 6 h after an initial decline. This increase was not found with B. fragilis mono-infections. The numbers of E. coli increased rapidly in both mono- and mixed infections and stayed high for several days, but only mixed infection resulted in abscesses that persisted for more than 7 days. Macrophages, the main component of the peritoneal cellular defence mechanism, were outnumbered by polymorphonuclear leucocytes during the first 6 h of infection. Further characterisation of the macrophage population by means of monoclonal antibodies showed a shift from resident to exudate macrophages as the result of influx of the latter.

Abdomen↗
PubMed1989

Epidemiology of the Bacteroides fragilis group in the colonic flora in 10 patients with colonic cancer.

We report the relative frequencies of members of the Bacteroides fragilis group in the faeces, in colon lavage fluid obtained pre-operatively, and in colonic tissue specimens obtained at operation from 10 patients with colonic cancer. B. vulgatus was the most and B. fragilis and B. ovatus were the least frequently isolated Bacteroides spp. in the faeces of the 10 subjects. B. uniformis and B. thetaiotaomicron ranked second and third in the faeces. The relative frequencies of all species except B. fragilis were lower in the lavage fluid and in cultures of mucosa. The relative frequency of B. fragilis increased from 4% in faeces to 39% in the final lavage fluid and to 42% in the colonic mucosa culture. Our results suggest that B. fragilis has a more intimate association with the gut mucosa than other members of the B. fragilis group, which might be one explanation for the high incidence of this species in gut-associated intra-abdominal infections.

Adult↗
PubMed1987

Differences in virulence within the species Bacteroides gingivalis.

In order to gain insight into the relative importance of several virulence factors of Bacteroides gingivalis, 8 strains with a varying virulence were studied. The virulence of B. gingivalis was determined in a mouse model. Strains HG 66, HG 76 and HG 184 were very virulent causing phlegmonous abscesses with lesions and necrosis. The strains HG 405 and HG 462 caused phlegomonous abscesses with pus. Strains HG 91, HG 94 and HG 185 were less virulent and induced gravity abscesses. In vitro strains HG 66, HG 76 and HG 184 induced low amounts of chemiluminescence by polymorphonuclear leucocytes. All other strains including HG 405 and HG 462 caused a relatively high chemiluminescence. Most strains displayed a high sensitivity to the bactericidal activity of fresh serum except for the highly virulent strains HG 66, HG 76 and HG 184. No differences in extracellular proteolytic activity on Azocoll, production of volatile fatty acids and ammonia were found between the B. gingivalis strains studied. In conclusion, differences in virulence were shown within the species B. gingivalis; the relative importance of several virulence factors was investigated.

Ammonia↗
PubMed1987

Effect of Bacteroides fragilis cellular components on chemotactic activity of polymorphonuclear leukocytes towards Escherichia coli.

Chemotaxis of polymorphonuclear leukocytes (PMNL) in response to cell components of Bacteroides fragilis alone or in combination with Escherichia coli was evaluated. E. coli produced much more powerful chemotactic factors than B. fragilis. The culture filtrate (CF), outer membrane (OM) preparation, and lipopolysaccharide (LPS) of B. fragilis slightly stimulated chemotactic activity of PMNL. The culture filtrate and OM preparation were capable of inhibiting the chemotaxis of PMNL in response to the chemotactic factors of E. coli but LPS of B. fragilis was not able to do so. Reduction by B. fragilis of PMNL chemotaxis in response to E. coli was not specific for B. fragilis but also occurred in the presence of facultative bacteria. In parallel with chemotaxis, lysozyme release, but not beta-glucuronidase release, by PMNL was significantly stimulated by E. coli but not by B. fragilis.

Bacterial Outer Membrane Proteins↗
PubMed1986

Effect of Bacteroides fragilis grown in the presence of clindamycin, metronidazole and fusidic acid on opsonization and killing of Escherichia coli.

Bactericidal action of human polymorphonuclear leucocytes on Escherichia coli in the presence of Bacteroides fragilis grown in subinhibitory concentrations of clindamycin, metronidazole and fusidic acid was studied. Bacteroides fragilis grown in the absence of drugs significantly inhibited the killing of Escherichia coli. Bacteroides fragilis grown in the presence of the drugs had a reduced inhibitory effect on the killing of Escherichia coli but this reduction was only significant for Bacteroides fragilis grown in 1/2 MIC of clindamycin. The phagocytosis of Bacteroides fragilis grown with and without clindamycin, as measured by killing, was the same. Complement consumption of Bacteroides fragilis grown with and without clindamycin did not differ. Clindamycin-treated Bacteroides fragilis fixed C3 to a significantly lower degree than did untreated bacteria. The chemiluminescence of Escherichia coli opsonized with serum preincubated with clindamycin-treated Bacteroides fragilis was significantly higher than with serum preincubated with untreated bacteria. These results suggested that in killing experiments of mixed Escherichia coli and Bacteroides fragilis, the mechanism underlying the reduced inhibitory capacity of clindamycin-exposed Bacteroides fragilis is related to greater availability of C3 in serum for opsonization of Escherichia coli.

Anti-Bacterial Agents↗
PubMed1986

Pathogenic synergy between Escherichia coli and Bacteroides fragilis or B. vulgatus in experimental infections: a non-specific phenomenon.

The virulence of Bacteroides fragilis and B. vulgatus for mice was compared in a skin-infection model. These strains were also tested for pathogenic synergy in mixed infections with Escherichia coli. Strains of B. fragilis were generally more virulent than strains of B. vulgatus and, with one exception, the effect of Bacteroides strains in mixed infections merely reflected their inherent virulence.

Animals↗
PubMed1986

Haemagglutination by the Bacteroides fragilis group.

Adhesive properties of five species of Bacteroides were compared by direct haemagglutination with erythrocytes of different origin. Only strains of Bacteroides fragilis agglutinated erythrocytes and different patterns of haemagglutination were observed. None of eight carbohydrates tested inhibited haemagglutination. The activity was destroyed by heat and by periodate treatment, but not by three proteases tested.

Adhesiveness↗
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↗
PubMed1985

Pathogenic synergy between Escherichia coli and Bacteroides fragilis: studies in an experimental mouse model.

An animal model is described for quantitative evaluation of pathogenic synergy between Escherichia coli and Bacteroides fragilis in which adjuvants were not required for abscess formation. Two sets of strains of E. coli and B. fragilis isolated from human wound infections were tested. Pathogenic synergy was observed in only one of the two combinations and was dependent on properties of E. coli.

Abscess↗