Pulsed-field gel electrophoresis, plasmid profiles and phage types for the human isolates of Salmonella enterica serovar Enteritidis obtained over 13 years in Taiwan

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Abstract
Aims: Plasmid profile, phage typing, and pulsed-field gel electrophoresis (PFGE) patterns of 124 Salmonella Enteritidis strains isolated in 1998–2002 in Taiwan were analysed and the results were compared with those of the 63 strains obtained in 1991–1997, so that molecular subtypes and epidemic strains for Salmonella Enteritidis over a 13-year period (1991–2002) could be elucidated. Methods and Results: A total of 124 strains of Salmonella Enteritidis isolated from human in Taiwan between 1998 and 2002 were analysed by PFGE, plasmid analysis and phage typing. The results obtained were compared with those of the 63 strains obtained in 1991–1997, so that the clonal relationships for a total of 187 strains obtained over 13 years could be elucidated. For PFGE, restriction enzymes XbaI, SpeI and NotI were used for chromosomal DNA digestion. Results showed 28 PFGE pattern combinations for the 187 Salmonella strains. Of them, pattern X3S3N3 was the major subtype as 130 strains isolated from different locations during 1991–2002 showed this PFGE pattern. For all these 187 strains, the genetic similarity was higher than 80%. Plasmid analysis showed 17 distinct types, which consist of one to four plasmids and the predominant phage type of those strains was PT4 (71·6%) and PT6a (13·4%). The three methods identified different degrees of polymorphism in the following order: plasmid profile (18 types, D = 0·659) > PFGE (28 types, D = 0·512) > phage typing (13 types, D = 0·438). As PFGE patterns, phage type and plasmid profile were combined for subtyping, the 187 strains could be grouped into 46 subtypes and the discriminatory index was raised to 0·795. For these 46 subtypes, the predominant one was X3S3N3/P1/PT4, which contained 77 (41%) isolates. Conclusions: Most of the Salmonella Enteritidis strains from sporadic cases were with pattern X3S3N3. They were the prevalent and may be the epidemic strains found in Taiwan during 1991–2002. The present study suggested that the several variants were derived from a single clonal line and the genome for strains of Salmonella Enteritidis are highly conserved over a 13-year period (1991–2002). Significance and Impact of the Study: The results obtained here are useful for epidemiolgical study of salmonellosis caused by Salmonella Enteritidis in Taiwan. Comparing the data of the present study with those obtained for strains from other countries, the major subtypes for Salmonella Enteritidis infection in the world can be elucidated.

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