The Combined Strategy of Baicalin and Oxacillin Sodium Against Methicillin-Resistant Staphylococcus aureus: Biofilm Inhibition, Virulence Attenuation and In Vivo Anti-Infection Efficacy

Over the past few years, considerable scholarly interest has been directed toward the synergistic application of natural compounds alongside conventional antibiotics to address infections stemming from multidrug-resistant (MDR) pathogens. The primary objective of this research is to investigate the efficacy of baicalin (BA), an extract obtained from Scutellaria baicalensis, when used in conjunction with oxacillin sodium (OXS). Specifically, the study evaluates their combined impact on biofilm formation and toxicity reduction in methicillin-resistant Staphylococcus aureus (MRSA) strain USA300. Furthermore, a murine peritonitis model induced by MRSA USA300 was developed to determine the therapeutic potential of this combination therapy against infection. Experimental data indicate that the co-administration of BA and OXS does not induce hemolysis in vitro. In comparison to treatments involving either BA or OXS alone, the combined regimen significantly enhances the accumulation of intracellular reactive oxygen species (ROS) within MRSA USA300. Additionally, this synergistic approach suppresses the production of extracellular polymeric substances (EPSs), decreases the overall protein content within the biofilm matrix, and impairs the metabolic functions of biofilm cells. The investigation also revealed that the synergistic application of BA and OXS intensifies the suppression of key virulence determinants, specifically lipase activity and staphyloxanthin production, while simultaneously downregulating the transcription of sarA (a global regulator of virulence). These findings substantiate the anti-virulence efficacy of the BA-OXS combination. In a murine model of peritonitis established using MRSA USA300, the healthy mice group, the MRSA USA300 group, the BA group, the OXS group, the combined group of BA and OXS, and the VAN group were set up, with eight mice in each group. The results showed that the combined therapy significantly mitigated body weight reduction, decreased the circulating counts of inflammatory cells, including leukocytes and lymphocytes, and suppressed the secretion of pro-inflammatory mediators such as TNF-α, IL-6, and IL-1β, thereby demonstrating potent anti-inflammatory properties. Furthermore, the co-administration of BA and OXS reduced bacterial burden in the abdominal organs of infected mice and alleviated associated histopathological injuries. Importantly, the treatment regimen exhibited no hepatorenal toxicity in the peritonitis mice, effectively maintaining normal levels. In the plasma of mice suffering from peritonitis, the concentration of malondialdehyde (MDA), a marker of oxidative stress, was reduced, while the activities of catalase (CAT) and superoxide dismutase (SOD) were elevated. This modulation contributes to anti-infective effects. These findings offer a theoretical foundation for subsequent investigations into the synergistic application of natural compounds and conventional antibiotics against MRSA.