Susceptibility of Haemophilus influenzae to chloramphenicol and eight beta-lactam antibiotics

In vitro activity of second and third generation cephalosporins against ampicillin susceptible and resistant haemophilus influenzae

One hundred seventy-five clinical isolates of Haemophilus influenzae (including 74 beta-lactamase-producing strains) were examined for susceptibility to ampicillin, cefonicid, cefamandole, cefuroxime and cefotaxime. Cefonicid and cefamandole exhibited similar activity against ampicillin-susceptible strains (MIC90 = 0.2 mg/l for both antibiotics); cefuroxime was slightly less active (MIC90 = 0.01 mg/l). However, cefonicid, cefuroxime and cefotaxime were all more active against beta-lactamase-producing H. influenzae than cefamandole (MIC90 = 1.0 mg/l for cefonicid, MIC90 = 2.0 mg/l for cefuroxime, MIC90 = 0.01 mg/l for cefotaxime, MIC90 = 5.0 mg/l for cefamandole). One hundred twenty-five of the 175 isolates were also tested for susceptibility to cefonicid and cefamandole by disc diffusion technique and a plot of zone diameter vs. MIC was analyzed for the beta-lactamase-producing strains.

Haemophilus influenzae: antibiotic susceptibility

Ampicillin resistance was first reported among clinical isolates of Haemophilus influenzae in 1972. Reports of chloramphenicol resistance followed shortly thereafter. The principal mechanism of resistance to these two antibiotics is enzymatic. Although other mechanisms have been described, they are found in comparatively few strains. The genetic information for the inactivating enzymes is plasmid mediated and therefore readily transmissible to susceptible strains. Consequently, effective therapy for invasive disease caused by this pathogen has been seriously compromised. As antibiotic susceptibility became less predictable, in vitro testing became increasingly important. Unfortunately, the standardization of methods for laboratory testing has been slow and complicated by the fastidious nature of the organisms. This review traces the development of antibiotic resistance in H. influenzae, discusses the mechanisms which appear to be important in mediating resistance, explores newer antimicrobial agents which might be useful in the treatment of infection, and analyzes the various approaches to in vitro testing.

Cefuroxime treatment of bacterial meningitis in infants and children

Recently, ampicillin- and chloramphenicol-resistant strains of Haemophilus influenzae type b and multiply-resistant Salmonella strains have appeared in some areas of the world. Therefore, alternative drug therapy for infections caused by these organisms is being sought. We used cefuroxime to successfully treat five children with H. influenzae type b meningitis and two children with Salmonella meningitis. Four H. influenzae type b isolates and one Salmonella isolate were resistant to ampicillin, chloramphenicol, and cotrimoxazole. Each of the patients received 200 to 250 mg of cefuroxime per kg per day in four divided doses for 14 to 21 days. The concentrations of cefuroxime in cerebrospinal fluid at 2 h after intravenous 50-mg/kg doses were 6.4 +/- 1.7 (mean +/- standard deviation) and 3.6 +/- 2.2 micrograms/ml on days 2 and 14 of treatment, respectively. The level of drug in cerebrospinal fluid was 1.34 +/- 1.3 micrograms/ml in children without meningitis. The mean cefuroxime concentration in subdural fluid samples from each of three patients was 12.6, 15, and 25.2 micrograms/ml. Cefuroxime is recommended as an alternative drug for the treatment of H. influenzae type b meningitis, but additional information is necessary before cefuroxime can be recommended for therapy of Salmonella meningitis.