Synergistic Evaluation of Ciprofloxacin with Plant Essential Oils against Salmonella Spp. Isolated from Animal Origin

Abstract

Foodborne salmonellosis caused by Salmonella spp. represented a major public health concern, further complicated by multidrug-resistant (MDR) strains. This study assessed the distribution, antibiotic resistance, and synergistic potential of plant essential oils (EOs) with ciprofloxacin (CIP) against Salmonella isolates from animal-based food samples collected in Faisalabad, Pakistan. Out of 105 samples, 41 (39%) were found positive for Salmonella, with the highest distribution in beef (73%) and mutton (67%). Antibiotic susceptibility testing revealed high resistance to co-trimoxazole (78%), ampicillin (76%), and ceftriaxone (76%), while CIP resistance was observed in 49% of isolates. Four EOs clove (CEO), thyme (TEO), tea tree (TTEO), and rosemary (REO)—were evaluated for antibacterial activity; CEO exhibited the largest inhibition zones (20–24 mm) and the lowest MIC values (250–500 µg/mL).Checkerboard assays showed that CIP–CEO combinations produced the strongest synergistic effect (FICI 0.39–0.47), CIP–TTEO displayed partial synergy (FICI 0.72–0.75), CIP–TEO demonstrated additive effects (FICI 0.88–0.92), and CIP–REO combinations were antagonistic (FICI 1.10–1.19). These results indicated that specific EOs, particularly CEO and TTEO, enhanced CIP efficacy against MDR Salmonella spp., suggesting a potential strategy to reduce antibiotic doses and mitigate antimicrobial resistance.

Keywords: Salmonella spp., Ciprofloxacin, Essential oils, Synergistic effect, foodbornemicrobes