rpoS -Regulated Core Genes Involved in the Competitive Fitness of Salmonella enterica Serovar Kentucky in the Intestines of Chickens

Abstract

e Salmonella enterica serovar Kentucky has become the most frequently isolated serovar from poultry in the United States over the past decade. Despite its prevalence in poultry, it causes few human illnesses in the United States. The dominance of S. Kentucky in poultry does not appear to be due to single introduction of a clonal strain, and its reduced virulence appears to correlate with the absence of virulence genes grvA, sseI, sopE, and sodC1. S. Kentucky's prevalence in poultry is possibly attributable to its metabolic adaptation to the chicken cecum. While there were no difference in the growth rate of S. Kentucky and S. Typhimurium grown microaerophilically in cecal contents, S. Kentucky persisted longer when chickens were coinfected with S. Typhimurium. The in vivo advantage that S. Kentucky has over S. Typhimurium appears to be due to differential regulation of core Salmonella genes via the stationary-phase sigma factor rpoS. Microarray analysis of Salmonella grown in cecal contents in vitro identified several metabolic genes and motility and adherence genes that are differentially activated in S. Kentucky. The contributions of four of these operons (mgl, prp, nar, and csg) to Salmonella colonization in chickens were assessed. Deletion of mgl and csg reduced S. Kentucky persistence in competition studies in chickens infected with wild-type or mutant strains. Subtle mutations affecting differential regulation of core Salmonella genes appear to be important in Salmonella's adaptation to its animal host and especially for S. Kentucky's emergence as the dominant serovar in poultry.A ccording to the Centers for Disease Control and Prevention, an estimated 1 million cases of human disease due to salmonellosis occur annually in the United States (1). Salmonella outbreaks are often associated with the consumption of contaminated meat and eggs (2). While more than 2,000 Salmonella serovars have been identified, 20 Salmonella serovars account for 73% of salmonellosis cases in the United States (3). Salmonella enterica Enteritidis and S. enterica serovar Typhimurium are the top two serovars associated with outbreaks in the United States (3) and are responsible for 50% of human infections worldwide (4). The serovar S. Kentucky is rarely associated with human illnesses in the United States (0.18% of cases) (3); however, it is the most prevalent serovar in poultry in the United States (5, 6).The emergence of S. Kentucky as the dominant serovar in poultry is similar to the emergence of S. Enteritidis in the 1980s (7), except that S. Enteritidis quickly became the leading cause of human salmonellosis in many countries (8), including the United States (9). There has been extensive research on S. Enteritidis, focused especially on identifying factors that contribute to colonization and egg transmission (10). While S. enterica subspecies I serovars share many metabolic and virulence pathways, forming a Salmonella core genome (11,12), there are differences with regard to the distribution of mobile genetic elements (prophage...

Phenotypic Prediction: Linking in vitro Virulence to the Genomics of 59 Salmonella enterica Strains

“…Most of the virulence genes that have a positive association with P(inf) were plasmid and phage associated genes (Table 2). Cheng et al (2015) mentioned that the disease incidence of poultry strains in humans may be attributable to the distribution of phage-associated virulence genes sodCI, sopE , and sseI and the plasmid located spvB in S . enterica serovars.…”

Impact of Dietary Galacto-Oligosaccharide (GOS) on Chicken’s Gut Microbiota, Mucosal Gene Expression, and Salmonella Colonization

“…Similar differences in competitive fitness have also been reported between S . Kentucky and ST in coinfected chickens S. Kentucky and ST/SE ( 27 , 28 ). Furthermore, challenging birds prior to molt with a non-SE serovar before exposure to SE has been shown to reduce SE-associated problems during molt ( 29 ), indicating that delayed coinfection in older birds also results in out competition of SE.…”

Salmonella spp. in poultry: a constant challenge and new insights

“…The experimental infection of two day old broiler chickens has revealed that serovar Kentucky persisted longer in the cecum comparing to Typhimurium and the peak was noted at 25 days pi (Cheng et al, 2015). Compared to S. Typhimurium, the expression of genes regulated by RNA polymerase sigma S factor (rpoS) was more pronounced in serovar Kentucky in the ceca content.…”