Efficacy of Amikacin Combinations for Nocardiosis

Efficacy of Amikacin Combinations for Nocardiosis

KEIJI KANEMITSU, HIROYUKI KUNISHIMA, TOMOO SAGA, HIDEO HARIGAE, SHIHO ISHIKAWA, HIROMU TAKEMURA¹ and MITSUO KAKU

Department of Molecular Diagnostics, Tohoku University Graduate School of Medicine, Sendai 980-8574, and ¹Department of Microbiology, St. Marianna University School of Medicine, Kawasaki, Kanagawa 261-8511

We isolated five bacterial strains from patients diagnosed as having nocardiosis. Bacterial species were identified based on the similarities in the nucleotide sequences of 16S ribosomal RNAs. Three of the five strains were identified as Nocardia asteroids, but unexpectedly other two were Streptomyces hygroscopicus and Rothia dentocariosa. The latter two species are not members of the family Nocardiaceae. We investigated the susceptibilities of these five strains to the following nine antimicrobial agents: trimethoprim/sulfamethoxazole (TMP/SMX), minocycline (MINO), erythromycin (EM), amikacin (AMK), cefotaxime (CTX), faropenem (FRPM), imipenem (IPM), ciprofloxacin (CPFX), and sparfloxacin (SPFX). The minimum inhibitory concentration (MIC) ranges (mg/ml) were as follows: TMP-SMX, 4->32; MINO, 0.125-8; EM, ≦0.016->32; AMK, 1-2; CTX, 0.063->32; FRPM, 0.063-16; IPM, 0.125-2; CPFX, 4-32; and SPFX, 0.5-16. Moreover, the synergistic effects of AMK in combination with each of TMP-SMX, MINO, EM, CTX, IPM, and SPFX were investigated by checkerboard synergy testing. No antagonism was recognized for the three N. asteroides strains. Synergistic and additive effects were observed for the combinations of AMK with CTX, IPM, or SPFX.

keywords —— nocardiosis; amikacin; combination therapy; FIC index

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Tohoku J. Exp. Med., 2003, 201, 157-163

Address for reprints: Keiji Kanemitsu, Department of Molecular Diagnostics, Tohoku University Graduate School of Medicine, 1-1 Seiryomachi, Aoba-ku, Sendai 980-8574, Japan.

e-mail: kane2@mail.cc.tohoku.ac.jp