ABSTRACT
Background and Aim: Post-weaning diarrhea associated with Escherichia coli is a major challenge in pig production, particularly with the increasing prevalence of multidrug-resistant (MDR) strains. Oregano oil has antimicrobial properties and may provide an alternative to conventional antibiotics. This study evaluated the in vitro antibacterial activity of oregano oil emulsion (OOE) against bacterial isolates, including MDR E. coli from diarrheic pigs, and compared its therapeutic efficacy with enrofloxacin in piglets with naturally occurring diarrhea.
Materials and Methods: E. coli was isolated from fecal samples of 11 diarrheic pigs and identified using culture and biochemical tests. Antimicrobial susceptibility to six antibiotics was determined using the Kirby–Bauer disk diffusion method. The minimum inhibitory concentration (MIC) of OOE was evaluated by agar dilution. For the therapeutic trial, 26 weaned piglets were allocated by litter into two groups (n = 13/group). Piglets received either 5% enrofloxacin orally once daily or OOE at 1 mL/2 kg body weight orally twice daily until fecal scores normalized. Fecal scores, bacterial counts, and weight gain were evaluated.
Results: All field E. coli isolates were resistant to at least two tested antibiotics. Resistance was highest to amoxicillin (100%), followed by amoxicillin–clavulanic acid and enrofloxacin (81.81% each). OOE inhibited field isolates at MICs of 2.5–10 mg/mL. Fecal scores decreased in both treatment groups, reaching 0 by day 7; however, enrofloxacin-treated piglets had greater odds of lower fecal scores (odds ratio = 6.11; 95% confidence interval = 1.23–30.44; p = 0.0274). Bacterial counts declined significantly over time (p < 0.0001), with no treatment effect (p = 0.727) or treatment × day interaction (p = 0.793). Weight gain did not differ between OOE (0.73 ± 0.14 kg) and enrofloxacin (0.71 ± 0.33 kg) groups (p = 0.884).
Conclusion: OOE exhibited antibacterial activity against antibiotic-resistant swine E. coli isolates and produced progressive clinical and bacterial count improvements in diarrheic piglets. Although enrofloxacin produced faster improvement in fecal consistency, OOE achieved fecal score resolution by day 7, with bacterial count reduction and weight gain comparable between treatments. These findings support further evaluation of OOE as a potential non-antibiotic approach for managing E. coli-associated diarrhea in pig production.
Keywords: antimicrobial resistance, antibiotic alternative, carvacrol, diarrheic piglets, Escherichia coli, multidrug resistance, oregano oil emulsion, post-weaning diarrhea.