Synergistic, biofilm inhibition, and antibacterial efficacy of (+)-catechin against methicillin-resistant Staphylococcus aureus and Pseudomonas aeruginosa: in silico and in vitro insights

Methicillin-resistant Staphylococcus aureus (MRSA) and Pseudomonas aeruginosa have been identified as major constituents of multidrug-resistant (MDR) bacteria, representing a substantial concern to global health. This study aims to test the antibacterial, biofilm-inhibitory, and synergistic effects of (+)-catechin against the three ATCC reference S. aureus strains (29213, 9144, and 25923), two ATCC reference P. aeruginosa strains (10145 and 9027), and MDR clinical isolates ( n = 30) collected from urinary tract infections in patients from Baghdad, Iraq. In silico and in vitro models were used to evaluate the influence of catechin on the expression of genes involved in the formation of P. aeruginosa and MRSA biofilms. Synergistic interactions with seven antimicrobials were also evaluated. Catechin showed significant antibacterial activity against MRSA and P. aeruginosa (MIC ranges of 1–4 µg/mL and 2–8 µg/mL, respectively) with biofilm inhibition of ≥ 60% for MRSA and ≥ 75% for P. aeruginosa . Strong synergism was observed with the catechin-azithromycin combination against both bacteria: MRSA (80% synergy) and P. aeruginosa (100% synergy). Catechin showed high affinity for the FnbA protein in MRSA and the AlgD protein in P. aeruginosa according to in silico and gene expression analysis. This study represents the first report of the downregulation of the biofilm-associated protein AlgD in P. aeruginosa and FnbA in MRSA. However, further in vitro assays to explore the full mechanism behind catechin action is warranted.