[Molecular analysis of Salmonella enteritidis by pulsed-field gel electrophoresis]

To study the relationship between different strains of Salmonella enteritidis, a molecular epidemiologic analysis method-pulsed-field gel electrophoresis was established and Salmonella enteritidis isolated from food samples were tested.

Food samples were collected from Henan province, Heilongjiang province and other provinces in 1991 - 2001. Strains were isolated and single colony of each Salmonella enteritidis strain from an agar plate was picked and enriched, then the total DNA was extracted in turn with lysozyme solution, proteinase K solution and TE buffer. The agarose pulgs were digested with restriction enzyme XbaI overnight at 37 degrees C, followed by pulsed-field gel electrophoresis (PFGE) with a CHEF Mapper system in 0.5 x TBE buffer with recirculation at 14 degrees C . DNA macrorestriction fragments were resolved on 1% agarose gels, pulse time were ramped from 5s to 45s during a 26h run at 6V/cm. A lambda ladder pulsed-field gel maker was used as a size standard.

30 Salmonella enteritidis strains were identified in chicken, beef, cooked meat and vegetables. 18 strains were isolated from henna province. More of the stains (22 strains) were isolated in 2001. Two distinct DNA fragment profiles, PFGE types A and B, were observed, representing 63.3% and 36.7% of the isolates respectively. Type A could be subdivided further into two subtypes. Subtype A1 represented the majority (78.9%) of type A strains and differed from subtype A2 in that the latter lacked a band in the 50kb region. There was no correlation between the strains profiles and their isolation time or region. However, all the strains isolated from the chicken were totally type A1, and showed certain epidemiological trend which can be studied in the future.

The pulsed-field gel electrophoresis is a good method to study the molecular epidemiological relationship between the different Salmonella enteritidis srtains.