Development of a new molecular subtyping tool for Salmonella enterica serovar Enteritidis based on single nucleotide polymorphism genotyping using PCR

The lack of a sufficiently discriminatory molecular subtyping tool for Salmonella enterica serovar Enteritidis has hindered source attribution efforts and impeded regulatory actions required to disrupt its food-borne transmission. The underlying biological reason for the ineffectiveness of current molecular subtyping tools such as pulsed-field gel electrophoresis (PFGE) and phage typing appears to be related to the high degree of clonality of S. Enteritidis. By interrogating the organism's genome, we previously identified single nucleotide polymorphisms (SNP) distributed throughout the chromosome and have designed a highly discriminatory PCR-based SNP typing test based on 60 polymorphic loci. The application of the SNP-PCR method to DNA samples from S. Enteritidis strains (n = 55) obtained from a variety of sources has led to the differentiation and clustering of the S. Enteritidis isolates into 12 clades made up of 2 to 9 isolates per clade. Significantly, the SNP-PCR assay was able to further differentiate predominant PFGE types (e.g., XAI.0003) and phage types (e.g., phage type 8) into smaller subsets. The SNP-PCR subtyping test proved to be an accurate, precise, and quantitative tool for evaluating the relationships among the S. Enteritidis isolates tested in this study and should prove useful for clustering related S. Enteritidis isolates involved in outbreaks.

Molecular study of Salmonella enteritidis in poultry samples by PCR, plasmid curing, antibiotic resistance and protein pattern analysis

In this study two control isolates of Salmonella enteritidis, RTCC1623 and RTCC1624, were obtained from the institute ofRazi (Karaj-Iran) and 14 strains were isolated from poultry samples in Kermanshah province of Iran, according to a standard protocol. These isolates were confirmed by PCR amplification of SefA gene fragments. Results showed that, 6 isolates of 14 isolates of Salmonella which their biochemical tests were positive contain 511 bp amplified fragments of the SefA gene. In other purpose, to correlating the presence of plasmids with antibiotic resistance and protein pattern, plasmid DNA was isolated before and after plasmid curing by using the alkaline lysis method. Strains of S. enteritidis contain seven different plasmid profiles (P1-P7) which were characterized by antibiotic resistance and protein pattern. Our observed showed, there was a high molecular weight plasmid with Rf 0.17 in all strains and the frequency of other plasmids was low. The plasmid with Rf about 0.2 is responsible for resistance to Cephalothin and the isolates that lost it were susceptible to this antibiotic. All strains, 100%, were resistant to ampicillin before and after curing of strains. According to present findings, PCR is a rapid and sensitive method for typing of S. enteritidis and plasmid profiling; antibiotic resistance and protein pattern are suitable methods for subtyping of S. enteritidis isolates. No direct correlation was found between plasmid contents, antibiotic resistance patterns and protein profiles of local S. enteritidis isolates.

Characterisation of local isolates of Enterobacteriaceae from Turkey

20 local isolates of enterics belonging to the genera Salmonella, Enterobacter, Proteus, Citrobacter from human, chicken and/or egg were characterised for their antibiotic resistance patterns, plasmid profiles, phage types, outer membrane proteins, and lipopolysaccharide patterns. Relatedness of these characteristics for epidemiological analysis was assessed. 18 (90%) strains were resistant to at least one antibiotic and those (multi-drug resistant ones) resisting to two or more antibiotics constituted 50% of all isolates. A common 54 kb plasmid was harboured by 55% of the isolates. 14 isolates showed smooth type lipopolysaccharide. 60% of the 20 isolates contained outer membrane proteins in a molecular weight range of 34.6 to 30.6 kDa. The data reveal the lack of correlation between the characteristics investigated.