Clinical Isolates Of Haemophilus Influenzae Research Articles

In vitro activity of temocillin against gram-negative clinical isolates.

120 consecutive clinical isolates of various species of Enterobacteriaceae and 30 consecutive clinical isolates of Haemophilus influenzae (including 5 which produced beta-lactamase) were assessed for susceptibility to temocillin using a broth microdilution technique and both 'light' (10(3) CFU/ml) and 'heavy' (10(6) CFU/ml) inocula. At the lighter inoculum, 90% of the Enterobacteriaceae were inhibited by temocillin at a concentration of 4 mg/L. 90% of the H. influenzae were similarly inhibited at a concentration of 0.5 mg/L, and no differences were observed between producers and non-producers of beta-lactamase. At the heavier inoculum, a significant inoculum effect was observed: minimum inhibitory concentrations (MICs) increased up to 128-fold for H. influenzae and somewhat less than that for the Enterobacteriaceae. Klebsiella pneumoniae was least affected by inoculum, showing only a 2- to 4-fold increase in the MIC. It is concluded that temocillin is active in vitro against the species tested and warrants further clinical trial.

In-vitro activity of imipenem against 100 strains of serotype b and nontypable Haemophilus influenzae, including strains resistant to ampicillin, chloramphenicol or both.

Imipenem, along with ampicillin, chloramphenicol, ceftazidime, aztreonam and ceftriaxone were tested against 100 clinical isolates of Haemophilus influenzae. Eighty-eight of the isolates were serotype b, 35 isolates were beta-lactamase producers, and five isolates were chloramphenicol resistant. Inoculum densities of 1 X 10(3), 1 X 10(5) and 1 X 10(8) cfu/ml were tested for all isolates. MIC90s and MBC90s at the two lower inoculum densities for imipenem, ceftazidime, aztreonam and ceftriaxone were in the susceptible range for all categories of isolates tested. Imipenem, ceftazidime and aztreonam displayed elevated MBC90s at the high inoculum density. The effect of the high inoculum density upon the ceftriaxone MBC90 was below the level of detection afforded by the study design.

Activities of newer β-Lactam antibiotics agsinst ampicillin, chloramphenicol, or multiply-resistant Haemophilus influenzae

The susceptibilities of singly or multiply-resistant clinical isolates of Haemophilus influenzae were determined by agar dilution to aztreonam, imipenem, and six third-generation cephalosporins. These included selected isolates that were resistant to ampicillin only, chloramphenicol only, and four isolates that were resistant to ampicillin, chloramphenicol, and trimethoprim-sulfamethoxazole. All of the isolates were highly susceptible to these newer β-lactam antibiotics. Isolates resistant to trimethoprim-sulfamethoxazole and/or chloramphenicol had susceptibilities similar to those of strains resistant only to ampicillin. Ceftriaxone, ceftizoxime, and cefotaxime were the most active of the study antibiotics ( MIC 90 = 0.004–0.016 μg/ ml), and were also bactericidal at concentrations no more than twice the minimum inhibitory concentration (MIC). Minimum inhibitory concentrations of cefoperazone increased dramatically with only a 10-fold increase in inoculum size of β-lactamase producing strains, while MICs of the other new agents were not significantly affected by elevation of the inocolum. These new antibiotics appear to be promising candidates for therapy of infections due to resistant H. influenzae .

In vitro activity of rosoxacin against Haemophilus influenzae.

The in vitro activity of rosoxacin was compared to that of ampicillin, cefoxitin, chloramphenicol, and rifampin, against 94 clinical isolates of Haemophilus influenzae. The results indicated that rosoxacin had significantly better in vitro activity against H. influenzae than the other antibiotics evaluated in this study. In addition, rosoxacin was an effective antimicrobial agent against isolates of H. influenzae that were resistant to ampicillin due to beta-lactamase production.

Interrelationships between physical state, phenotypic stability and transferability of beta-lactamase genes in Haemophilus influenzae.

SUMMARY: We have evaluated 66 β-lactamase-producing (β-Lac+) clinical isolates of Haemophilus influenzae for the presence of plasmid DNA, ability to conjugate with an H. influenzae type b recipient, and stability of the β-Lac+ phenotype. Of the 66 strains, 23 (35%) contained a plasmid demonstrable by either of two methods of cleared cell lysate preparation. The molecular weight of 17 of the plasmids was approximately 30 x 106. Four strains carried a plasmid of mol.wt 3 x 106 and single strains carried plasmids of mol. wt 36 x 106 or 50 x 106. Of 23 plasmids that were unstable in vitro, 10 (43%) had molecular weights of 30 x 106 and coded only for β-lactamase. Stability of the β-Lac+ phenotype was observed in all 43 strains in which plasmid DNA was not demonstrated by physical methods. When β-Lac+,‘plasmid-free’ strains were conjugated with strain Eagan (H. influenzae type b), ampicillin-resistant transconjugants were isolated in 21 out of 43 matings (the lower limit of detection was 10-7 per donor cell per 30 min mating). With few exceptions, homologous (type b x type b) crosses with β-Lac+, plasmid-containing donors were more efficient (frequency 10-2—10-3) than heterologous (untypable x type b) matings (frequency 10-6-10-7). β-Lac+,‘plasmid-free’ strains were inefficient donors (frequency 10-6-10-7) irrespective of serotype, but all transconjugants from these crosses were efficient donors (frequency 10-1-10-4) and contained a plasmid of mol. wt 30 x 106 that was unstable in 9 cases out of 26 (35%). The increase in transferability and phenotypic instability of plasmid-bearing β-Lac+ strains reinforces the concept of a chromosomal locus for β-lactamase genes in‘plasmid-free’ β-Lac+ strains. Carriage of β-lactamase genes on 30 x 106 mol. wt R plasmids aids transferability at the expense of genetic stability.

Die biochemische Charakterisierung von Haemophilus-Stämmen mit Hilfe der API 20E- und API 50E-Testsysteme

Abstract The commercially available test systems API 20E and API 50E were used to characterize 74 reference strains and clinical isolates of Haemophilus influenzae, H. aegyptius, H. parainfluenzae, H. paraphropbilus and H. paraphrohaemolyticus . The strains were grown on chocolate agar followed by suspending some colonies in proteose pepton medium, pH 7.6, supplemented with the X- and V-factors. The alkaline suspension was used to inoculate the cups of the test kits. The alkali of the medium did not influence the biochemical reactions of the bacteria and enabled elimination of false positive reactions, particularly with the indicator phenol red. The API-systems proved efficacious for the diagnosis and characterization of the strains as compared with conventional biochemical tests.