Evaluation of Pine oil in combination with Colistin against Multi-Drug Resistant Escherichia coli strains Isolated from Poultry

Abstract

Poultry contributes greatly to the health and economic development of the world. Antibiotic-resistant E. coli is the primary cause of mortality and production loss in poultry. Escherichia coli is a highly resistant, gram-negative, pathogenic, and rod shaped bacteria. Infections caused by pathogenic E. coli are becoming harder to treat due to the rise of antibiotic-resistant strains. The rise of antibiotic resistance is a worldwide issue that affects both human and animal health. To combat this issue, new methods are needed to prevent resistance from spreading and to prolong the effectiveness of existing antibiotics such as the use of essential oils as antibiotics. This study aimed to enhance the potency of conventional antibiotics that are used against E. coli by combinational therapy. Colistin with Pine oil and Colistin with Oxytetracycline are two combinations that were analyzed for their effect on certain virulence factors of E. coli. Colistin is used as 1st line of drugs in poultry and Pine oil is used to keep the farm environment germs-free. For the evaluation of both combinations, 89 isolates of E. coli were processed for antimicrobial susceptibility testing; disc diffusion, MIC, and biofilm formation. The results of disc diffusion revealed 100% and 51.68% resistance in Oxytetracycline and Colistin respectively, while 100% susceptibility was observed by Pine oil. Biofilm assay presents 14.6% of isolates form biofilm and 85.3% do not develop biofilm. MIC results show 96% highest resistance against Oxytetracycline. In the case of Colistin, there is evidence of some resistance, but the resistance falls within the lower ranges of MIC. The FICIs for an antibiotic combination of Colistin and Oxytetracycline were calculated against E. coli based on the minimum inhibitory concentration of each agent. The Colistin and Oxytetracycline combination inhibits the growth of E. coli more efficiently than individual antibiotics, showing a 100% synergistic effect. Whereas, the combination of Colistin with Pine oil shows a 100% antagonistic effect against all tested MDR strains of E. coli that were measured by the disc diffusion method and evaluated by comparison of inhibition zones. The result of the current study concludes that the combination of Colistin with Oxytetracycline is a better substitute against E. coli than the combination of Colistin with Pine oil.