Characterization of the virulence regions in the plasmids of three live Salmonella vaccines

Suitability of repetitive-DNA-sequence-based PCR fingerprinting for characterizing epidemic isolates of Salmonella enterica serovar Saintpaul

Three molecular typing methods, repetitive-sequence-based PCR (rep-PCR) fingerprinting, plasmid profiling, and arbitrarily primed PCR fingerprinting, were used to characterize isolates of Salmonella enterica serovar Saintpaul. Most of the isolates were obtained from epidemic human cases of food-borne salmonellosis, together with some from the food material suspected to be the source of infection, and a few were obtained from other cases apparently not related to the epidemic. All three methods adequately discriminated the epidemic strain from other strains of the serovar. In addition several isolates from human cases which are not identical to the epidemic strain were found. These isolates therefore must have been responsible for some sporadic infections, which were only temporally related to the epidemic. These strains showed a high degree of similarity to a strain isolated from a turkey. rep-PCR fingerprinting with REP-Dt primers and primer ERIC1R, applicable even to crude cell lysates, offers an attractive choice as a primary method for the discrimination of various Salmonella serotypes as well as isolates within serotype Saintpaul.

Molecular characterization of Salmonella enterica subsp. enterica serovar choleraesuis field isolates and differentiation from homologous live vaccine strains suisaloral and SC-54

Four independent molecular methods were used to characterize the Salmonella enterica subsp. enterica serovar choleraesuis live vaccine strains SC-54 and Suisaloral and to differentiate them from S. choleraesuis field isolates. Plasmid analysis revealed the presence of seven plasmid profiles. A virulence plasmid of 52-kbp was identified by hybridization with an spvB-spvC gene probe in each of the S. choleraesuis field isolates and in the Suisaloral vaccine strain, but not in the SC-54 vaccine strain. Ribotyping, performed with a gene probe that recognized 23S, 16S, and 5S rRNA genes, resulted in three closely related hybridization patterns. IS200 elements were not detected in the field isolates or in the two S. choleraesuis live vaccine strains. Macrorestriction analysis with the enzymes XbaI, SpeI, NotI, and SfiI differentiated the 29 S. choleraesuis strains included in this study into 10, 13, 8, and 13 different fragment patterns, respectively. While the Suisaloral vaccine strain showed a unique XbaI macrorestriction pattern, the fragment patterns of the SC-54 strain obtained with the different enzymes were shared by 2 to 18 S. choleraesuis field strains. A combination of plasmid analysis and macrorestriction analysis proved to be most suitable for the molecular typing of S. choleraesuis and the differentiation of both live vaccine strains from field isolates of this serovar.

Evaluation and comparison of molecular techniques for epidemiological typing of Salmonella enterica subsp. enterica serovar dublin

A total of 28 unrelated isolates of the Salmonella enterica subsp. enterica serovar dublin (S. dublin) collected during a 6-year period, as well as four samples of the S. dublin live vaccine strain Bovisaloral and its prototype strain S. dublin 442/039, were investigated by different molecular typing methods for the following reasons: (i) to find the most discriminatory method for the epidemiological typing of isolates belonging to this Salmonella serovar and (ii) to evaluate these methods for their capacity to discriminate among the live vaccine strain Bovisaloral, its prototype strain S. dublin 442/039, and field isolates of the serovar dublin. Five different plasmid profiles were observed; a virulence plasmid of 76 kbp as identified by hybridization with an spvB-spvC gene probe was present in all isolates. The detection of 16S rRNA genes and that of IS200 elements proved to be unsuitable for the epidemiological typing of S. dublin; only one hybridization pattern could be observed with each of these methods. The results obtained from macrorestriction analysis strongly depended on the choice of restriction enzyme. While the enzyme NotI yielded the lowest discriminatory index among all enzymes tested, it was the only enzyme that allowed discrimination between the Bovisaloral vaccine strain and its prototype strain. In contrast to the enzymes XbaI and SpeI, which only differentiated among the S. dublin field isolates, XhoI as well as AvrII also produced restriction fragment patterns of the Bovisaloral strain and of its prototype strain that were not shared by any of the S. dublin field isolates. Macrorestriction analysis proved to be the most discriminatory method not only for the epidemiological typing of S. dublin field isolates but also for the identification of the S. dublin live vaccine strain Bovisaloral.

Use of ribotyping, IS200 typing and plasmid analysis for the identification of Salmonella enterica subsp. enterica serovar Typhimurium vaccine strain Zoosaloral H and its differentiation from wild type strains of the same serovar

Fifty Salmonella enterica subsp. enterica serovar Typhimurium (S. Typhimurium) isolates obtained from one vaccinated and three non-vaccinated poultry flocks as well as the commercially available vaccine strain Zoosaloral H and a S. Typhimurium reference strain were characterized genotypically to differentiate between S. Typhimurium live vaccine strain Zoosaloral H and wild type strains of the same serovar. Ribotyping revealed five different patterns one of which exclusively occurred in the vaccine strain. Seven different hybridization patterns could be observed by IS200-typing of the S. Typhimurium isolates; one of them was only detectable in the vaccine strain. Plasmid analysis showed that 51% of the S. Typhimurium isolates including the vaccine strain harboured large plasmids of approximately 60 MDa. Hybridization with a virulence gene probe identified only 48% of these large plasmids, including that of the vaccine strain, to carry this virulence-associated gene. However, restriction endonuclease analysis of the hybridizing plasmids showed that the virulence gene was located on HindIII fragments of different sizes in the plasmid of the S. Typhimurium vaccine strain Zoosaloral H and in the plasmids of the respective wild type S. Typhimurium isolates. Thus, ribotyping, IS200-typing and plasmid analysis represent at least three independent systems which allow the genotypic identification of the S. Typhimurium vaccine strain Zoosaloral H and its differentiation from wild type isolates of the same serovar.