Egyptian Apis mellifera bee propolis modulating resistance of Staphylococcus aureus to antibiotics

Staphylococcus aureus remains a significant challenge due to its persistent antibiotic resistance, highlighting the urgent need for alternative antibacterial agents. Our study explored the resistance-modulatory potential of two Egyptian propolis samples against 68 clinical S. aureus isolates (61 MRSA and 7 MSSA). We assessed methicillin resistance and antibiotic susceptibility, further evaluating propolis resistance modulatory and synergistic effects using specific methodologies, including the checkerboard method. Antibacterial potency was determined via broth microdilution, while HPLC characterized its chemical profile. We differentiated strains using spa typing and investigated propolis direct cellular effects through time-kill assays and transmission electron microscopy. HPLC analysis showed distinct chemical profiles for Egyptian propolis extracts (PEE), with unique constituents influencing their effects. Western-Nile PEE had an average MIC of 0.6470 ± 0.0375 mg/mL, while Upper-Egypt PEE averaged 0.445 ± 0.012 mg/mL. Upper-Egypt PEE demonstrated significantly lower MBCs against S. aureus ATCC strains (P = 0.0203 for MRSA), though no significant MIC difference was noted between PEE types for standard strains (P > 0.9999). Effects on clinical isolates varied. Propolis exhibited significant resistance modulation, with modulatory factors ranged from 2 to 590 leading to MIC reductions of 50-99.83%. For example, propolis reduced ciprofloxacin MIC by 75% for MRSA ATCC 43,300 (P = 0.0022) and 98.44% for MDR clinical isolates (P = 0.0027). Vancomycin showed the most significant combined inhibitory effect (P < 0.0001). Checkerboard assays confirmed a powerful synergistic effect (ΣFIC ranged from 0.037 to 0.06; P < 0.05) while transmission electron microscopy revealed obvious severe damage to bacterial cell wall integrity. Egyptian propolis represents a promising resistance modulator and antimicrobial agent. This study adopted a comprehensive approach to investigate the antibacterial and resistance-modifying properties of two Egyptian propolis samples collected from different regions against Staphylococcus aureus. Ethanolic extracts were prepared and further analyzed by High Performance Liquid Chromatography (HPLC) for chemical profiling. Various methodologies were employed, beginning with the recovery and identification of Staphylococcus aureus from diverse clinical specimens, followed by antibiotic susceptibility profiling across different classes. Methicillin resistance was phenotypically confirmed via cefoxitin screening and genotypically by molecular detection of the mecA gene. Virulence determination and strain differentiation were achieved through single-locus sequence typing of the spa gene. To evaluate propolis intrinsic antibacterial activity broth microdilution method was utilized. This was complemented by time-kill assays and transmission electron microscopy to determine dose and time-dependent killing kinetics and effect on cell wall, respectively. Resistance modulation was assessed by specific approach and antibiotic resistance and its synergistic potential with a panel of antibiotics was investigated using the checkerboard method. All generated data underwent appropriate statistical analysis to ensure result significance.