CONTRIBUTION OF SALMONELLA ENTERITIDIS VIRULENCE FACTORS TO INTESTINAL COLONIZATION AND SYSTEMIC DISSEMINATION IN DAY-OLD CHICKENS
Addwebi, Tarek Mohamed
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Salmonella enterica serovar Enteritidis (S. Enteritidis) is one of the most common serovars associated with poultry and poultry product contamination in the USA. We previously identified fifteen mutant strains of S. Enteritidis phage type 4 (PT4) with significantly reduced invasiveness in human intestinal epithelial cells (Caco-2), chicken macrophages (HD-11) and chicken hepatocellular epithelial cells (LMH). These included S. Enteritidis mutants with transposon insertions in newly identified S. Enteritidis-specific genes (pegD and SEN1393), and genes or genomic islands common to most other Salmonella serovars (SEN0803, SEN0034, KsgA, SEN2278 and SEN3503) along with eight genes previously known to contribute to enteric infection (hilA, pipA, fliH, fljB, csgB, spvR, and rfbMN). We hypothesized that S. Enteritidis employs both common Salmonella enterica colonization factors and S. Enteritidis-specific traits to establish infection in chickens. Four S. Enteritidis mutants (SEN0034::Tn5, fliH::Tn5, SEN1393::Tn5 and spvR::Tn5) were indistinguishable from the isogenic wild-type strain when orally inoculated in one-day-old chickens whereas two mutants (CsgB::Tn5 and PegD::Tn5) were defective for intestinal colonization (P < 0.05) and nine mutants (hilA::Tn5, ksgA::Tn5, SEN3503::Tn5, SEN0803::Tn5, SEN2278::Tn5, fljB::Tn5, rfbM::Tn5, rfbN::Tn5 and pipA::Tn5) showed significant in vivo attenuation in more than one organ (P < 0.05). Complementation studies confirmed the role of rfbN and SEN3503 during infection. This study should contribute to a better understanding of the pathogenic mechanisms involved in S. Enteritidis pathogenesis, and the genes identified here could potentially serve as targets for the development of live-attenuated or subunit vaccine.