In vitro and in vivo activities of minocycline and other antibiotics against Acinetobacter (Herellea-Mima).

Minocycline was the most active of six antibiotics tested against 65 clinical isolates of Acinetobacter calcoaceticus (syn.: Herellea, Mima) received from six medical centers. In the Bauer-Kirby disk susceptibility test, all isolates were rated susceptible to minocycline, gentamicin, and polymyxin; 25% were resistant to tetracycline. In agar dilution tests, minocycline was two to four times more potent than gentamicin or polymyxin and eight times more potent than tetracycline. Ampicillin and cephalexin were relatively ineffective. Against lethal infections produced by five strains of A. calcoaceticus in mice, minocycline was, in general, more active than gentamicin or polymyxin on a dosage basis and significantly more active on a blood-level basis. Minocycline was significantly more potent than tetracycline on both dosage and blood-level bases against tetracycline-sensitive and -resistant strains. In the last decade there has been an increase in the reported incidence of acinetobacters in a variety of infections. The cultures are susceptible to few antibiotics. Our data show that minocycline could offer an effective alternative to the more toxic drugs for the treatment of these infections. Susceptibility should be determined with minocycline disks.