Investigating the synergistic antimicrobial effect of carvacrol and zinc oxide nanoparticles against Campylobacter jejuni

Campylobacter is a leading cause of foodborne gastroenteritis worldwide. Campylobacter contamination along the poultry production chain is believed to greatly contribute to human infections. Antibiotics are widely used in poultry industry to prevent infections as well as enhance animal growth, but the use of antibiotics is believed to be an important factor that promotes the emergence and dissemination of antibiotic-resistant Campylobacter. Alternative antimicrobial strategies will be beneficial to reduce the prevalence of this microbe in agri-foods and avoid the emergence of antibiotic resistance. Synergistic antimicrobial approach is to combine several antimicrobials of different mechanistic actions that can reduce the dosage of individual antimicrobial and expand the spectrum of antimicrobial activity. In this study, carvacrol and zinc oxide nanoparticles (ZnO NPs) were investigated regarding their synergistic antimicrobial effect against Campylobacter jejuni. The single treatment of either carvacrol or ZnO NPs at low concentration only generated a bacteriostatic effect. In contrast, the combination of carvacrol and ZnO NPs resulted in a bactericidal effect that significantly enhanced the antimicrobial efficacy. The mechanism of action of this synergism was investigated from both phenotypic and genotypic perspectives of C. jejuni using Raman spectroscopy and real-time quantitative polymerase chain reaction (RT-qPCR). Carvacrol was the inducing factor to damage the cell membrane and increase the susceptibility of C. jejuni, followed by the treatment of acting factor ZnO NPs to physically induce cell leakage. This study provides an alternative strategy to inactivate C. jejuni and demonstrates its potential to be applied in food industry against other foodborne pathogens.