Arbekacin, an aminoglycoside antibiotic, has antibacterial activity against both Gram-positive and Gram-negative bacteria and is stable in the presence of aminoglycoside-inactivating enzymes produced by methicillin-resistant Staphylococcus aureus (MRSA). In this report, the antibacterial activity of arbekacin was compared with that of vancomycin, a glycopeptide antibiotic that also has potent antibacterial activity against MRSA. Arbekacin showed concentration-dependent bactericidal activity against MRSA strain 1936 (0.5-2 x MIC), but vancomycin showed only slight bactericidal activity, even at high concentrations of 19 x MIC. Arbekacin showed a longer post-antibiotic effect (2.3-3.8 h) than vancomycin (0-1.3 h) against MRSA strain 1936. Arbekacin induced marked morphological changes at 0.5 x MIC and the changes remained for 2 h after removal of the agent. When exposed to 0.5 x MIC of vancomycin, no notable morphological change was observed in the treated cells. Since arbekacin has broad-spectrum activity, these findings suggest that it may be a useful agent against MRSA infection, especially for polymicrobial MRSA infection with Gram-negative bacilli, such as Pseudomonas aeruginosa.

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