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

Eighty-four isolates of penicillin-resistant pneumococci were tested for susceptibility to vancomycin, rifampicin, cotrimoxazole, and 14 beta-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 X 12, 0 X 25, 0 X 5 mg/l, respectively). Cefoxitin and latamoxef were the least active of the drugs studied. The remaining beta-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 beta-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.