In vitro synergism between mnocycline and amikacin against clinical isolates of gram-negative bacilli

Akira Watanabe, Masako Sasaki, Seiichi Aonuma, Kotaro Oizumi, Kiyoshi Konno

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    4 Citations (Scopus)

    Abstract

    In vitro inhibitory effects of minocycline in combination with amikacin on the growth of a total of 107 clinical isolates of gram-negative bacilli were examined by a checker board dilution method. Following strains were included in this experiment ; 15 strains of P. aeruginosa, 18 strains of E. 25 strains of pneumoniae and 49 strains of Serratia marcescens (20 of the 49 strains were epidemic strains of a nosocomial episode in Iwaki City Hospital). The average fractional inhibitory concentration index (FIC index) of minocycline in combination with amikacin against E. and K. pneumoniae was 0.43. Thus, the combined effects were found to be synergistic. The average FIC index against P. aeruginosa was 0.63, that against Serratia marcescens 0.56 and that against the epidemic strains in Iwaki City Hospital 0.73. Thus, it was found that the inhibitory effects of minocycline in combination with amikacin on the growth of P. aeruginosa and Serratia was not synergistic, but only additive. Four of 107 strains tested were selected at random and the effects of minocycline in combination with amikacin on the growth of the above four strains was examined in broth by counting the viable cells. In a strain of Serratia, on which the inhibitory effect of minocycline in combination with amikacin had exerted antagonistic effects, as evaluated by a checker board dilution method, the combined effects on growth in broth was antagonistic as well. The growth inhibitory effects of minocycline plus amikacin on one strain each of E.coli, K.pneu-moniae and Serratia were confined by a checker board dilution method, and then experiments of similar nature in broth were undertaken. The number of viable cells in two-drug experiment, in which the concentrations of both drugs were below 1 MIC, decreased at 2 hour of incubation to less than 1 : 1,000 as compared with that found in the single-drug experiment. Thus, it was found that minocycline in combination with amikacin, at the concentrations below 1 MIC each, exerted a synergistic and bactericidal action against these 3 strains.

    Original languageEnglish
    Pages (from-to)308-315
    Number of pages8
    JournalChemotherapy
    Volume30
    Issue number3
    DOIs
    Publication statusPublished - 1982 Jan 1

    ASJC Scopus subject areas

    • Pharmacology (medical)
    • Infectious Diseases
    • Pharmacology
    • Drug Discovery
    • Oncology

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