Caffeic Acid and Erythromycin: Antibacterial and Synergistic Effects on Staphylococci

Background: Antibiotic-resistant bacteria, especially Staphylococcus species, are a growing concern in healthcare settings and infections caused by multidrug-resistant strains are difficult to treat. Therefore, it is imperative to explore new treatment methods for these infections such as combinations of natural compounds with antibiotics. Methods: The main objective of this study was to investigate the antimicrobial activity of caffeic acid against staphylococcal strains. The viability of bacterial cells and half maximal inhibitory concentration (IC₅₀) for caffeic acid were also examined. The minimum inhibitory concentration (MIC) of the caffeic acid was determined using a serial microdilution method. To study the combined effect of caffeic acid and erythromycin, the fractional inhibitory concentrations (FICs) were determined. Results: Caffeic acid inhibited the growth of all the tested isolates, with MIC values ranging from 256 to 1024 µg/mL and reduced bacterial cell viability at concentrations corresponding to MIC values. Caffeic acid and erythromycin showed a synergistic effect when used together against three examined strains and had an additive effect against two isolates. However, their combination was indifferent against the seven remaining staphylococci tested. Conclusions: The results of our research demonstrate that caffeic acid has antimicrobial properties against the tested strains.