Submitted to: Avian Pathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/20/2008
Publication Date: 8/21/2008
Citation: Li, S., Zhang, Z., Pace, L., Zhang, S., Lillehoj, H.S. 2008. Functions exerted by the virulence-associated type 3 secretion systems during Salmonella enterica serovar Enteritidis infection of chicken oviduct epithelial cells and macrophages. Avian Pathology. 38:97-106.
Interpretive Summary: Salmonella enterica serovar Enteritidis (SE) is a predominant etiologic agent of non-typhoidal salmonellosis, accounting for 18.6% of all cases in the US according to CD report in 2007. Consumption of SE-contaminated poultry products remains a risk factor for human SE outbreaks and epidemiological studies demonstrate that contamination of raw poultry products with Salmonella is attributable to cross-contamination in the hatchery from infected or contaminated fertilized eggs to uninfected chicks. Earlier studies showed that the pathogenicity island-1 (SPI-1) and SPI-2 of Salmonella enterica encode two virulence associated type three secretion systems, namely T3SS-1 and T3SS-2, respectively. Mutations in the genes encoding secretion appraratus, translocases, or certain effectors has been shown to develop attenuated phenotypes in terms of either invasion or intracellular replication. A recent study suggested that inactivation of ssrA, a regulator of T3SS-2, rendered SE unable to successfully colonize chicken oviduct. In this study, Scientists at the Mississippi State University, College of Veterinary Medicine and ARS have investigated the pathogenic roles of individual effectors of T3SS-1 and T3SS-2 in SE invasion and intracellular survival in chicken oviduct epithelial cells and macrophages. This study shows that (1) both T3SS-1 and T3SS-2 are required by SE to invade COEC; (2) SipA and PipB are necessary for the survival of SE in chicken COEC and PBLM, respectively; and (3) T3SS-2 triggers PBLM death during the early stage of SE infection and this process does not depends on PipB. This new information is important to develop a novel vaccine strategy against salmonellosis for poultry scientists at academia and industry.
Technical Abstract: Salmonella enterica serovar, Enteritidis (SE) infection of chicken is a major contributing factor to non-typhoidal salmonellosis. The roles of the type three secretion systems (T3SS-1 and T3SS-2) in the pathogenesis of SE infection of chickens are poorly understood. In this study, the functions exerted by T3SS-1 and T3SS-2 during SE infection of primary chicken oviduct epithelial cells (COEC) and macrophages were characterized. The T3SS-1 and T3SS-2 null mutants (sipB and ssaV) were significantly less invasive than their wild type parent strain. The genes encoding effector proteins of T3SS-1 (SipA, SopB, and SopE2) and T3SS-2 (PipB) contributed equally to the entry of SE into COEC. The sipA mutant showed a reduced survival and the pipB mutant displayed an enhanced replication in COEC. Mutations in T3SS-2 genes, ssaV and pipB, impaired the survival of SE in chicken periphery blood leukocytes-derived macrophages (PBLM), but not in HD11, an established chicken macrophage cell line. A mutation in the ssaV gene also abolished SE-induced PBLM death from 1hpi to 4hpi. This study shows that (1) both T3SS-1 and T3SS-2 are required by SE to invade COEC; (2) SipA and PipB are necessary for the survival of SE in chicken COEC and PBLM, respectively; and (3) T3SS-2 triggers PBLM death during the early stage of SE infection and this process does not depends on PipB.