Antibiotic susceptibility of pneumococci and Haemophilus influenzae isolated from patients with acute exacerbations of chronic bronchitis: prevalence of tetracycline-resistant strains in Hong Kong.

The susceptibility of 119 respiratory isolates of Haemophilus influenzae and 87 respiratory isolates of Streptococcus pneumoniae to various antibiotics was tested by means of an agar dilution method and an inoculum size of 10(3) colony forming units (c.f.u.). The antibiotics tested included penicillin/ampicillin, erythromycin, tetracycline, chloramphenicol and four third-generation cephalosporins, cefotaxime, cefoperazone, ceftriaxone and moxalactam. Fifty-eight per cent of the pneumococcal strains and 23 per cent of the H. influenzae strains tested were found resistant to tetracycline (MICs = 4-128 mg/l and 4-64 mg/l, respectively). None of the isolates tested was resistant to erythromycin or chloramphenicol. Three per cent of Haemophilus strains tested were beta-lactamase producing and thus resistant to ampicillin (MICs = 2-8 mg/l), while none of the pneumococcal strains tested was penicillin-resistant. Three of the newer third-generation cephalosporins--cefotaxime, cefoperazone and ceftriaxone--were highly active against both H. influenzae and Str. pneumoniae while moxalactam, though also active, was comparatively less effective.