Virulence potential of five major pathogenicity islands (SPI-1 to SPI-5) of Salmonella enterica serovar Enteritidis for chickens.

BACKGROUND: Salmonella is a highly successful parasite of reptiles, birds and mammals. Its ability to infect and colonise such a broad range of hosts coincided with the introduction of new genetic determinants, among them 5 major pathogenicity islands (SPI1-5), into the Salmonella genome. However, only limited information is available on how each of these pathogenicity islands influences the ability of Salmonella to infect chickens. In this study, we therefore constructed Salmonella Enteritidis mutants with each SPI deleted separately, with single individual SPIs (i.e. with the remaining four deleted) and a mutant with all 5 SPIs deleted, and assessed their virulence in one-day-old chickens, together with the innate immune response of this host. RESULTS: The mutant lacking all 5 major SPIs was still capable of colonising the caecum while colonisation of the liver and spleen was dependent on the presence of both SPI-1 and SPI-2. In contrast, the absence of SPI-3, SPI-4 or SPI-5 individually did not influence virulence of S. Enteritidis for chickens, but collectively they contributed to the colonisation of the spleen. Proinflammatory signalling and heterophil infiltration was dependent on intact SPI-1 only and not on other SPIs. CONCLUSIONS: SPI-1 and SPI-2 are the two most important pathogenicity islands of Salmonella Enteritidis required for the colonisation of systemic sites in chickens.

Improved diagnostic and real-time pcr in rapid screening for Salmonella in the poultry food chain.

The goal of this study was to improve the diagnostic applicability of genus- and serovar- (S. Enteritidis and S. Typhimurium) specific PCR systems in screening faecal and caecal samples of poultry, poultry feed and poultrymeat for Salmonella, by keeping the opportunity to obtain Salmonella cultures from positive samples. Peptone broth pre-enrichment cultures of the samples were tested by PCR. In faecal and caecal samples from broiler chicks a strong inhibitory action was frequently observed. This could be reduced markedly by the addition of bovine serum albumin (BSA) acting as amplification facilitator. The results of testing pre-enrichment cultures from artificially contaminated faecal, poultry feed and poultrymeat samples (using S. Enteritidis, S. Typhimurium and S. Hadar as contaminants) suggest that the sensitivity of the above systems is 10(1)-10(2) CFU g(-1) sample. The testing of 95 caecal samples from slaughtered chicks resulted in 49% culture-positive and 76% PCR-positive samples. The suitability of a generic real-time PCR for testing faecal samples of poultry was also studied. Its detection limit for these samples was found to be lower than that of the diagnostic PCR system. Both methods reduced the time required for Salmonella detection to 24-30 h, and the advantage of the real-time PCR was its increased sensitivity. We have established a diagnostic and a real-time PCR system for rapid and reliable genus- and serovar- (S. Enteritidis and S. Typhimurium) specific detection of Salmonella for monitoring purposes in the poultry food chain. Sensitivity is equal to, or higher than, that of the standard bacterial culture method, and the method still provides the Salmonella culture if needed.