Abstract: [Objective] To investigate the antibacterial activities of several antibiotics,hyaluronic acid（HA） alone,and HA combined with penicillin （PEN） against Staphylococcus aureus（S.aureus）. [Method] The susceptibility of 1 standard strain and 9 clinical S.aureus strains isolated from dairy cattle to antimicrobial agents was evaluated using the double-dilution method and the micro-checkerboard method. [Result] The resistance rates of S.aureus to PEN,clindamycin and erythromycin were 90%,80% and 40%,respectively. No methicillin-resistant strains were detected,and 40% of the strains showed inducible clindamycin resistance. The combination of HA and PEN exhibited either additive effect （FICI 0.5~1.0） or synergistic effect （FICI≤0.5） against all tested S. aureus strains. [Conclusion] The combination of HA and PEN can significantly reduce the effective minimal inhibitory concentration of both agents against S.aureus,which provides a new idea for the clinical treatment of drug-resistant S.aureus infections.

Key words: hyaluronic acid（HA）, penicillin（PEN）, Staphylococcus aureus（S.aureus）, minimal inhibitory concentration（MIC）