ABSTRACT Staphylococcus aureus is an important human pathogen with a high potential for antibiotic resistance and zoonotic transmission. Doxycycline is widely used in human and poultry infections, but its extensive application has accelerated the emergence of resistant strains. This study evaluated the potential of tannic acid, salicylic acid, and boric acid as adjuvants to doxycycline against S. aureus isolated from frozen chicken meat. Isolates were identified using selective culture media and biochemical tests. Antimicrobial activity was determined by broth microdilution assays to measure minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values. Synergistic interactions were assessed using the fractional inhibitory concentration index (FICI), while antibiofilm activity was also investigated. In addition, molecular docking analysis was performed using the target protein structure (PDB ID: 4URO). Doxycycline showed a MIC value of 0.5 μg/mL, whereas tannic acid, salicylic acid, and boric acid exhibited MIC values of 500, 1000, and 2000 μg/mL, respectively. Combination treatments reduced the MIC of doxycycline to 0.125 μg/mL with tannic acid and 0.25 μg/mL with salicylic acid, confirming synergistic effects, while boric acid showed no synergism. MBC and biofilm inhibition assays further supported the enhanced antibacterial activity of doxycycline combined with tannic acid or salicylic acid. Molecular docking results were consistent with the biological findings, showing the strongest binding affinity for doxycycline (−6.92 kcal/mol), followed by tannic acid (−5.61 kcal/mol) and salicylic acid (−5.49 kcal/mol), whereas boric acid showed weak binding (−3.22 kcal/mol). Overall, tannic acid and salicylic acid significantly enhanced the antimicrobial and antibiofilm effects of doxycycline against S. aureus , suggesting their potential as natural adjuvants for combating antibiotic resistance.
Al‐Aklah et al. (Mon,) studied this question.
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