Enhancing activity of antibiotics against Staphylococcus aureus with Shuang-Huang-Lian

Staphylococcus aureus is a major pathogen in both hospitals and the community and can cause systemic infections such as pneumonia. Multi-drug resistant strains, such as Methicillin-resistant S. aureus (MRSA) are particularly worrisome. Bacterial antibiotic resistance can be attributed to various mechanisms including antibiotic inactivation. In order to reduce the development of bacterial resistance, we hypothesized that two selected traditional Chinese medicines, Shuang-Huang-Lian (SHL) and Lan-Qin, would be effective against S. aureus. In this study, we carried out the zone of inhibition determination of five antibiotics including amoxicillin, gentamicin, penicillin, clarithromycin, cefazolin and the traditional Chinese medicines SHL and Lan-Qin. The preliminary screening results showed that all the drugs except Lan-Qin exhibited antibacterial effects. Then, we conducted quantitative determination experiments to further explore the bacteriostasis of different drugs. The results of minimum inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs) determination indicated that penicillin had the best inhibitory effect on bacterial growth, and clarithromycin killed all the bacteria at the lowest concentration. Also, we tested the combined effect of SHL with different antibiotics against S. aureus and calculated the fractional inhibitory concentration (FIC) of the antibiotics. The results showed that SHL had a synergistic effect with gentamicin as well as additive effects with penicillin and cefazolin against S. aureus by decreasing MICs of antibiotics compared with using antibiotics alone. Our study provides a reference for the clinical treatment of S. aureus infection in combination with traditional Chinese medicines.