Microencapsulated essential oils as antibiotic alternatives in broiler chickens

Antimicrobial resistance (AMR) has become a serious problem in poultry farms that can threaten both poultry and human health. An increasing number of studies have been conducted on exploring antimicrobial alternative such as essential oils (EO). The objective of this study was to evaluate the effects of encapsulated EO including cinnamaldehyde (CIN) and citral (CIT) alone or in combination (CIN+CIT) on growth performance, meat quality, gut health, and AMR phenotypes, genotypes, and virulence of broiler chicken fecal Escherichia coli isolates, and zoonosis of poultry-isolated AMR extraintestinal pathogenic E. coli (ExPEC). Results showed the feed efficiency ratio (FCR), mortality (%), gut lesion scores were all reduced by bacitracin and encapsulated CIN, CIT, and CIN+CIT. Cecal microbiota was modulated in birds fed bacitracin, CIN, CIT, and CIN+CIT compared with birds fed basal diets. Furthermore, vaccinated birds showed altered cecal microbiota, reduced mortality (%) but higher gut lesions compared with nonvaccinated birds. The AMR levels (%) of chicken fecal E. coli to most tested antimicrobials were lower in birds fed encapsulated CIN or CIN+CIT which also showed reduced prevalence (%) of some antimicrobial resistance genes and plasmids. Additionally, bird age is also a factor affecting AMR phenotypes, genotypes, and virulence of chicken fecal E. coli. Encapsulated CIN improved apparent ileal nutrient digestibility, intestinal duodenal and jejunal villus/crypt ratio, jejunal gene expressions for nutrient transporters, and changed cecal and ileal intestinal microbiota. The ExPEC isolated from poultry meat and feces had significant effects on reducing survival (%) of Caenorhabditis elegans but the relationships between antimicrobial susceptibility or number of virulence genes with pathogenicity of E. coli isolates were not conclusive. In conclusion, encapsulated CIN has the potential to improve growth performance, gut health, meat quality, modulating ileal and cecal microbiota, and reduce resistance level (%) to antimicrobials and prevalence of antimicrobial resistance genes and plasmids in chicken fecal E. coli isolates. Additionally, ExPEC isolated from poultry meat or feces may possess zoonotic potential to cause human infections.