Summary auto-generated
This study analyzed the population structure of Serpulina hyodysenteriae, the causative agent of swine dysentery, using multilocus enzyme electrophoresis (MLEE) on 231 isolates from pigs and four from rheas. The isolates were divided into 50 electrophoretic types (ETs) with mean genetic diversity of 0.29. Analysis of the index of association (IA)—a measure of linkage disequilibrium—revealed that the IA for ETs (0.29±0.17) was not significantly different from zero, indicating genetic recombination. However, the IA for isolates (3.93±0.03) was significantly greater than zero, with seven ETs containing 51% of all isolates. This pattern indicates an epidemic population structure, where recombination has shaped the overall population, but certain successful clones have become widely disseminated globally. Serogroups were not distributed along distinct genetic lines, suggesting recombination may have modified genes involved in lipopolysaccharide synthesis. The findings demonstrate that despite high underlying recombination rates, S. hyodysenteriae has epidemic clones like ET 35 (36 isolates) that have spread across multiple geographical regions.
Key findings
- S. hyodysenteriae exhibits an epidemic population structure with evidence of significant genetic recombination at the electrophoretic type level, but certain successful clones dominate the overall population
- Seven of 50 electrophoretic types contain 51% of all 231 isolates, indicating widespread dissemination of epidemic clones globally, particularly ET 35 (36 isolates) and ET 20 (15 isolates)
- Serogroups are not distributed along distinct genetic lines, with 16 of 23 multi-isolate electrophoretic types containing more than one serogroup, suggesting recombination has modified genes involved in lipopolysaccharide synthesis
- High genetic diversity and haplotypic diversity (0.94) indicate relatively even distribution of isolates across electrophoretic types despite epidemic clonal dominance
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Abstract
The population structure of Serpulina hyodysenteriae was investigated using multilocus enzyme electrophoresis. A total of 231 isolates were divided into 50 electrophoretic types (ETs), with a mean genetic diversity of 0.29 for the number of ETs and 0.23 for the number of isolates. Subsets of isolates from two Australian states (71 isolates from Victoria and 68 isolates from Queensland) exhibited as much genetic variation as the entire collection. The calculated index of association (IA) for the number of ETs (0.29 +/- 0.17) was not significantly different from zero, and hence provided evidence for the occurrence of significant genetic recombination accounting for the observed variation between strains. In contrast, the IA for the number of isolates (3.93 +/- 0.03) was significantly different from zero, with seven of the 50 ETs (ETs 4, 6, 13, 14, 20, 33 and 35) containing 51% of all the isolates. Even when multiple isolates from the same farm were removed from the analysis, the IA value for the number of isolates remained significantly greater than zero (IA 9.87 +/- 0.04), indicating that it was not biased by their inclusion. The results suggest that S. hyodysenteriae has an epidemic population structure.