Diversity and molecular variation among plasmids inSalmonella entericaserotype Dublin based on restriction enzyme fragmentation pattern analysis

Abstract

SUMMARYMolecular variation within and between plasmids ofSalmonella enterica serotype Dublin was analysed. Such variation has been demonstrated in the serotypespecific plasmids (SSP's) of Typhimurium and Enteritidis. The two aims of this study were to determine the plasmid diversity in a host-adapted serotype and also the incidence of molecular variation in the SSP among strains of Dublin using restriction endonuclease fragmentation pattern (REFP) analysis with Pstl, Smal and EcoRV. Sixty-five strains were examined from seven countries. Plasmid profile and REFP analysis showed that none of the strains was plasmid-free. Seventy-seven percent of the strains possessed the 72 kb SSP either alone or in combination with another plasmid; 23 % harboured plasmids which were molecular variants of the SSP. Four of the variants were more closely related to each other than to the reference SSP and were harboured by Dublin isolated from both the USA and Europe. A further three were shown to be cointegrate plasmids and were similarly distributed. Thirty-two percent of strains possessed the SSP alone. None of the UK strains was resistant to any of the antimicrobial agents tested whereas 74 % of the remaining strains were resistant to between one and five antimicrobial agents. This study corroborates previous findings concerning the high degree of stability of the SSP and confirmed the clonal nature of Dublin.Co-resident plasmids provided evidence of sub-clones within localized geographical areas.

Molecular analysis of Salmonella enterica serotype Dublin: Building bridges between population genetic and molecular epidemiological studies

“…Population genetic studies of Dublin based on multilocus enzyme electrophoresis [24,251 argued in favour of two major clones Dul and Du3, the former world-wide in distribution and of PP80:3 or 80; the latter restricted to the UK and France of PP80, 8050, 80:40 or 40. A more detailed study of plasmids including REFP analysis of SAP variants among strains of Dublin indicated considerably greater diversity [23]. Whereas the plasmid profiles of some strains corresponded to presumed D u l and Du3 other strains harboured plasmids not reported in previous investigations and the geographical distribution of intermediate sized plasmids was extended.…”

An Evaluation of DNA-Based Methodologies for SubtypingSalmonella

“…Small plasmids contributed to the diversity of profiles. Browning et al (1995) found 15 plasmid profiles in 65 S. dublin strains from seven countries, including Denmark, but profiles did not …”

“…Browning et al (1995) reported plasmids in all 65 S. dublin isolates in their collection from seven countries. Threlfall et al (1994b) reported plasmids in 94% of 1089 S. enteriditis PT4 isolates, and Rankin et al (1995) found plasmids in 91% of 434 S. enteriditis isolates from Scotland and the U.S. Olsen et al (1992) detected plasmids in 88% of 1284 S. berta strains.…”

“…For generating plasmid fingerprints, plasmid DNA has usually been purified to improve digestion with restriction enzymes, for example, by using phenol-chloroform extraction, isopropanol precipitation, RNase treatment, and ethanol precipitation (Browning et al, 1995). Platt et al (1986) described a plasmid fingerprinting protocol for enterobacteria, including Salmonella.…”

“…Restriction digestions have been performed on total plasmid DNA containing multiple plasmid types (Dorn et al, 1993), but this approach does not determine the plasmid from which particular fragments have originated. Browning et al (1995) circumvented this dilemma by digesting total plasmid DNA of isolates in which the plasmid of interest was the sole plasmid. Olsen et al (1992) electrophoresed total plasmid DNA, sliced individual bands from the gel, and digested each plasmid size separately.…”