Investigating the Potential of Natural Antimicrobial Molecules for Reducing Samonella enterica serovar Enteritidis Colonization in Chickens

Salmonella Enteritidis is a major pathogen that causes foodborne human illness in the United States. Despite several control measures adopted for reducing the pathogen by pre-harvest and post-harvest approaches, Salmonella is widespread in poultry leading to elevated incidence rates. Epidemiological studies suggest that poultry and poultry products are the major vehicles for transmission of S. Enteritidis to humans. Chickens serve as natural hosts for S. Enteritidis with the cecum being the principal site of colonization. Cecal colonization of S. Enteritidis in birds leads to the contamination of carcasses during slaughter, contamination of eggshell with feces, and contamination of egg yolk, albumen and shell membranes by transovarian route. Therefore, reducing S. Enteritidis carriage in chickens is critical for reducing human infections. In this Ph. D. dissertation, the efficacy of three natural molecules, caprylic acid (CA), a medium chain fatty acid, and trans-cinnamaldehyde (TC) and eugenol (EG), two phytophenols, were investigated for reducing cecal colonization and fecal shedding of S. Enteritidis in chickens. In addition, cell culture studies, quantitative real-time PCR and DNA microarray were used to elucidate the molecular mechanisms behind the antimicrobial action of TC and EG. Results revealed that prophylactic and therapeutic supplementation of CA, TC and EG in feed significantly reduced S. Enteritidis populations in the cecum and cloaca of treated chickens, compared to the control birds (P \u3c 0.05). Feeding of CA, TC or EG did not adversely affect the body weight, feed intake, pH, or endogenous cecal bacterial population in treated chickens, compared to the negative controls. Follow up studies revealed that the natural molecules reduced S. Enteritidis motility and invasion of avian intestinal epithelial cells, in vitro (P \u3c 0.05). Real-Time quantitative PCR results indicated that the expression of major virulence genes such as hilA, hilD, invF, flhC , and motA in S. Enteritidis was reduced significantly by CA, TC and EG (P \u3c 0.05). The DNA microarray data revealed that the TC and EG exerted antimicrobial effect on S. Enteritidis by multiple mechanisms, including down-regulation of genes responsible for flagellar motility, Salmonella Pathogenicity Island 1, type three secretion system, translocation and effector proteins, hyb virulence operon, outer membrane proteins, cell division, transcription, translation, metabolism, biosynthetic pathways, and terminal electron acceptors. The efficacy of CA, TC and EG in reducing S. Enteritidis in chickens could be utilized in the control of the pathogen in chickens as a pre-harvest treatment for potentially decreasing foodborne diseases caused by the pathogen.