Comparative susceptibilities of penicillin-resistant pneumococci to co-trimoxazole, vancomycin, rifampicin and fourteen β-lactam antibiotics

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Abstract
Eighty-four isolates of penicillin-resistant pneumococci were tested for susceptibility to vancomycin, rifampicin, cotrimoxazole, and 14 β-lactam antibiotics by agar and microbroth dilution methods. Twenty-three were from adult patients with pneumococcal disease, 57 from nasopharingeal carriers (preschool children) and four were resistant South African isolates. For all isolates tested, imipenem (N-formimidoyl thienamycin), rifampicin, ceftriaxone and cefotaxime had the greatest activity (MIC90: 0.12, 0.25, 0.5 mg/1, respectively). Cefoxitin and latamoxef were the least active of the drugs studied. The remaining β-lactams tested had less activity than that of penicillin. All strains were inhibited by 1 mg/l of vancomycin and all but one were resistant to cotrimoxazole. The excellent in-vitro activities of the newer β-lactam agents (ceftriaxone, cefotaxime and, particularly, imipenem) and vancomycin against penicillin-resistant pneumococci offer a considerable promise for their use in the treatment of pneumococcal meningitis caused by these strains.