The Role of Antimicrobial Peptide Resistance Genes, virK and ybjX, during Salmonella enterica Serovar Enteritidis Infection in the Chicken Reproductive Tract



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Salmonella enterica serovar Enteritidis (S. Enteritidis) is a major etiologic agent of non-typhoid salmonellosis, which causes 1.028 million cases with approximately 400 deaths in the United States. S. Enteritidis persistently and silently colonizes the intestinal and reproductive tract of laying hens, resulting in contaminated poultry products. The consumption of contaminated poultry products has been identified as a significant risk factor for human salmonellosis. To understand the mechanisms S. Enteritidis utilizes to colonize and persist in laying hens, we used selective capture of transcribed sequences to identify genes over-expressed in the chicken macrophage cell line (HD11) and in primary chicken oviduct epithelial cells. From the 15 genes found to be overexpressed in both cell types, we characterized the antimicrobial peptide resistance genes (AMPR), virK and ybjX, in vitro and in vivo. In vitro, AMPR genes were required for natural morphology, motility, secretion, defense against detergents such as EDTA and bile salts, and resistance to antimicrobial peptides polymyxin B and avian ?-defensins. From this, we inferred the AMPR genes play a role in outer membrane stability and/or modulation. AMPR genes also played distinct roles in macrophage invasion and survival. In laying hens, both AMPR genes were involved in early intestinal colonization and fecal shedding. In the reproductive tract, virK was required in early colonization while a deletion of ybjX caused increased ovary colonization and egg deposition. In conclusion, data from the present study indicate that AMPR genes are differentially utilized in various host environments to defend against host immunity, with the possibility this is through mechanisms that modulate the outer membrane; this ultimately assists S. Enteritidis in persistent and silent hen colonization. Decoding the specific mechanisms employed by S. Enteritidis during colonization will aid in better control mechanisms to reduce this pathogen?s prevalence.