Combinatorial Approach: Potentiation of Ciprofloxacin by Silkworm- Derived Moricin against Pseudomonas aeruginosa Strains

Antimicrobial resistance (AMR) in Pseudomonas aeruginosa threatens the efficacy of last-line antibiotics like ciprofloxacin. Novel strategies, including combination therapy with natural antimicrobial peptides (AMPs), offer a pathway to potentiate existing drugs. This study evaluated the synergistic potential of silkworm-derived moricin combined with ciprofloxacin against clinical P. aeruginosa isolates. Three molecularly identified P. aeruginosa strains (PA03, PA065, PA076) were isolated from fish pond water. Minimum inhibitory concentrations (MICs) of moricin and ciprofloxacin, alone and in combination at nine ratios (9:1 to 1:9), were determined using broth microdilution. Moricin alone exhibited MICs of 0.125–0.500, while ciprofloxacin alone showed 0.125–0.250. Combination therapy produced ratio-dependent MIC reductions, with maximal potentiation at 3:7 and 2:8 ratios (moricin:ciprofloxacin). MICs decreased 2- to 7.9-fold compared to moricin alone (PA03: from 0.125 to 0.017; PA076: from 0.500 to 0.063). One-way ANOVA confirmed significant MIC reductions across combination ratios for all isolates (F = 22.8–28.4, df = 10, p < 0.001). Post-hoc analysis showed that 6:4 to 2:8 ratios produced significantly lower MICs than moricin alone (p < 0.01), while 9:1 and 8:2 ratios did not (p > 0.05). Combinatorial use of moricin and ciprofloxacin synergistically enhances anti-pseudomonal activity in a ratio-dependent manner, significantly reducing effective MICs. This study provides the first statistical evidence of moricin-ciprofloxacin synergy against Nigerian aquaculture-derived P. aeruginosa strains, demonstrating that optimized peptide-antibiotic ratios can resensitize resistant isolates, offering a low-toxicity pipeline for combating fluoroquinolone-resistant infections.