Modulatory effect of Canavalia gladiata lectin on quinolone activity against multidrug-resistant and efflux pump-positive Staphylococcus aureus

Clinically relevant bacteria have increasingly developed resistance to antimicrobial agents, reducing the effectiveness of conventional antibiotic therapies. In this context, antibiotic adjuvants capable of restoring or enhancing the activity of existing drugs represent a potential strategy against multidrug-resistant bacteria. This study evaluated the potential of a lectin isolated from Canavalia gladiata seeds (CGL) as an antibiotic-modulating agent against multidrug-resistant and efflux pump-positive bacterial strains. CGL was purified by affinity chromatography on Sephadex G-50, and its direct antibacterial activity was evaluated by determining the minimum inhibitory concentration (MIC). Its modulatory effects were subsequently assessed in combination with conventional antibiotics and in assays involving strains carrying the NorA and MepA efflux pumps. CGL showed weak intrinsic antibacterial activity against all tested strains, with MIC values ≥1,024 μg/mL. However, when used at a sub-inhibitory concentration, CGL moderately enhanced the activity of norfloxacin against Staphylococcus aureus 10, reducing the MIC from 256 to 170.6 μg/mL, and ciprofloxacin against S. aureus K2068, reducing the MIC from 32 to 13.3 μg/mL. These effects did not restore bacterial susceptibility to clinically established therapeutic breakpoints. In contrast, no significant enhancement was observed for the other antibiotic combinations, and some associations resulted in increased MIC values. Therefore, CGL does not appear to act as a direct antibacterial agent under the conditions evaluated, but may have potential as an antibiotic adjuvant, particularly in combination with quinolones against selected S. aureus strains. Further mechanistic, toxicity, and in vivo studies are required to determine its applicability as an antibiotic-modulating agent.