Caffeic Acid and Erythromycin: Antibacterial and Synergistic Effects on Staphylococci.

Antibiotic-resistant bacteria, especially 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. 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 (IC) 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. 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. The results of our research demonstrate that caffeic acid has antimicrobial properties against the tested strains.