Therapeutic potential of thymol, carvacrol, and biogenic silver nanoparticle against avian pathogenic Escherichia coli (APEC): alternatives to the use of antimicrobials.

Antimicrobial resistance represents a significant threat to global public health, and poultry production is a critical sector within this context. Since the use of antimicrobials in poultry farming can promote the selection of resistant bacterial strains, the search for effective alternatives is essential. Thymol and carvacrol, two aromatic monoterpenes, as well as biogenic silver nanoparticles (bio-AgNP) have antimicrobial potential. Therefore, the aim of this study was to evaluate the action of thymol, carvacrol, and bio-AgNP against multidrug-resistant (MDR) Escherichia coli strains with virulence factors of avian pathogenic E. coli (APEC), as well as the capacity to reduce the microbial population. of these compounds in a colibacillosis experimental infection. The antimicrobial activity of thymol, carvacrol, and bio-AgNP was evaluated in vitro against E. coli strains, and in vivo, assessing the therapeutical efficacy of thymol/carvacrol (500 and 1000 mg/kg) and bio-AgNP (25 and 51 mg/kg) in an experimental colibacillosis model. The cecal bacterial populations (APEC strain used for bacterial challenge and Enterobacteriaceae), were quantified, and their potential for translocation was evaluated. Although bio-AgNP, thymol, and carvacrol showed significant in vitro antimicrobial activity, the combination of these compounds at therapeutic doses was not effective to reduce the cecal bacterial population of APEC nor Enterobacteriaceae, even at high concentrations of the monoterpenes. The administration of bio-AgNP caused an increase in the body weight of broilers. Our findings indicate that, despite their antimicrobial efficacy in vitro assays, the therapeutic application of the compounds in vivo, under the evaluated conditions, did not result in significant antimicrobial benefits.