Submitted to: Avian Diseases
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/7/2001
Publication Date: 5/16/2001
Citation: Hudson,C.R.; Garcia,M.; Gast,R.K.; Maurer,J.J., Determination of close genetic relatedness of the major salmonella enteritidis phage types by pulsed-field gel electrophoresis and DNA sequence analysis of several salmonella virulence genes. Avian Diseases issue 45 pg. 875-886 Interpretive Summary: Identification of the source of bacterial contamination in food products is an important process especially in the event of an outbreak. This process has been particularly difficult when dealing with Salmonella enteritidis. In Europe, the bacteria appear to be distinct and readily discernible from one another. Conversely, differentiation of Salmonella enteritidis in the U.S. is not an easy process. In this study, three molecular typing methods (pulsed-field gel electrophoresis [PFGE], random amplified polymorphic DNA-PCR [RAPD-PCR], and DNA sequencing) were used for comparison to differentiate isolates of S. enteritidis. Of the three methods, RAPD-PCR was the best method for differentiation of the isolates. Neither PFGE nor DNA sequencing provided information necessary for distinguishing differences between the isolates suggesting that the bacteria are highly clonal. This investigation will be useful for scientists and other investigators when attempting to locate a source of S. enteritidis in outbreaks or contamination.
Technical Abstract: Salmonella enteritidis is an important cause of egg-associated outbreaks in both Europe and the United States. Phage typing has become an important epidemiological tool in identifying source of outbreaks. Limitations of phage typing have become apparent with wholesale egg distributors that have multiple suppliers in an area where a particular phage type is endemic. Several different molecular typing methods were evaluated for their discriminatory power to identify genetic differences among different S. enteritidis phage types isolated in Europe and the U. S. Pulsed-field gel electrophoresis (PFGE) identified a single DNA pattern among the different S. enteritidis (SE) phage types. Comparing the nucleotide sequence for several Salmonella virulence genes failed to identify a single nucleotide change in the gene sequences from most S. enteritidis isolates, regardless of phage type. Based on these results, it appears that the different S. enteritidis phage types are genetically related or clonal. However, using primers 1283 and Opa4, it was possible to not only differentiate SE isolates from different geographic locations, but within a specific geographic locale as well using Random Amplified Polymorphic DNA PCR. Any chance for discerning genetic differences among isolates will need to rely on molecular techniques other than PFGE.