In Vitro Antibacterial and Postantibiotic Effects of Enrofloxacin Combined With Sulfamonomethoxine Against Pathogenic Bacteria of Yellow Catfish (Pelteobagrus fulvidraco)

Abstract

Research on the synergistic effect of combined antibacterial agents has contributed significantly to addressing microbiological challenges, particularly bacterial resistance mutations. This study employed a combination of enrofloxacin (ENR) and sulfamonomethoxine (SMM) to conduct in vitro antimicrobial susceptibility tests and assess postantibiotic effects (PAEs) against three primary pathogens, Edwardsiella ictaluri, Aeromonas veronii, and Aeromonas hydrophila, known to afflict yellow catfish (Pelteobagrus fulvidraco). The results indicated that the minimum inhibitory concentrations (MICs) of ENR against E. ictaluri, A. veronii, and A. hydrophila were 0.25, 0.125, and 0.125 μg/mL, respectively. The MICs of SMM against these pathogens were 800, 700, and 700 μg/mL, respectively. Notably, the combination of ENR and SMM exhibited synergistic effects across all tested strains, increasing the PAE duration compared to ENR or SMM alone at the same concentration (p  < 0.05). In addition, the increase in PAE duration and enhanced antibacterial efficacy observed with the ENR–SMM combination demonstrated a positive correlation with the total drug concentration. These results suggest that the combination of ENR and SMM reduced the dosage of individual antibacterial agents while ensuring an efficient antibacterial effect. This approach holds promise for the treatment of bacterial infections in the yellow catfish.