Salmonella enterica subspecies enterica serovar Enteritidis Salmonella pathogenicity island 2 type III secretion system: role in intestinal colonization of chickens and systemic spread

Abstract

Salmonella enterica subspecies enterica serovar Enteritidis (S. Enteritidis) has been identified as a significant cause of salmonellosis in humans. Salmonella pathogenicity islands 1 and 2 (SPI-1 and SPI-2) each encode a specialized type III secretion system (T3SS) that enables Salmonella to manipulate host cells at various stages of the invasion/infection process. For the purposes of our studies we used a chicken isolate of S. Enteritidis (Sal18). In one study, we orally co-challenged 35-day-old specific pathogen-free (SPF) chickens with two bacterial strains per group. The control group received two versions of the wild-type strain Sal18: Sal18 attTn7 : : tet and Sal18 attTn7 : : cat, while the other two groups received the wild-type strain (Sal18 attTn7 : : tet) and one of two mutant strains. From this study, we concluded that S. Enteritidis strains deficient in the SPI-1 and SPI-2 systems were outcompeted by the wild-type strain. In a second study, groups of SPF chickens were challenged at 1 week of age with four different strains: the wild-type strain, and three other strains lacking either one or both of the SPI-1 and SPI-2 regions. On days 1 and 2 post-challenge, we observed a reduced systemic spread of the SPI-2 mutants, but by day 3, the systemic distribution levels of the mutants matched that of the wild-type strain. Based on these two studies, we conclude that the S. Enteritidis SPI-2 T3SS facilitates invasion and systemic spread in chickens, although alternative mechanisms for these processes appear to exist.

Utilization of Pyrosequencing to Monitor the Microbiome Dynamics of Probiotic Treated Poultry (<i>Gallus gallus domesticus</i>) during Downstream Poultry Processing

“…Interestingly, Wisner et al [35], showed that the Salmonella was cleared after 3 and 4 days of post challenge which suggests that testing the feces could have helped in finding specific inoculated bacteria.…”

A review of the ecology, colonization and genetic characterization of Salmonella enterica serovar Sofia, a prolific but avirulent poultry serovar in Australia

“…Desin et al (2009) states that S. Enteritidis mutants deficient in the entire SPI-1 (ΔSPI-1) were able to colonize chicken caeca at the same level as the non-mutant wildtype (wt). Mutant strains ΔSPI-1 and ΔSPI-2 were out-competed by wt strains during colonization but reached the same level of systemic spread at a slower rate than parent strains (Wisner et al, 2010). Together this suggests that changes within S. Sofia SPI-1 and 2 compared to S. Typhimurium may not play a major role in this organism's successful colonisation of chickens.…”

The Salmonella Pathogenicity Island-1 and -2 Encoded Type III Secretion Systems

“…To examine this, chickens were challenged orally with 10 6 -10 9 Salmonella bacteria. In co-challenge trials using 35-day-old chickens we showed that although a S. Enteriditis wild-type strain was only slightly more competitive in colonizing the ceca than mutants defective in SPI-1 and SPI-2, the systemic spread of both of these mutant strains to the liver and spleen was significantly less successful than that of the wild-type strain (Desin, et al, 2009, Wisner, et al, 2010. Colonization of the gut was nearly 100% for both wild-type and mutants, whereas Salmonella was detected in the liver and spleen in approximately 30% of the birds in these trials.…”