Pulsed-field gel electrophoresis (PFGE) was applied as a molecular typing tool for the
spirochaete Serpulina hyodysenteriae, the agent of swine dysentery. Analysis of a collection of
40 mainly Australian isolates, previously characterized by other methods, divided these into 23
PFGE types. This confirmed that there are many strains of the spirochaete in Australia. PFGE
was more discriminatory for strain typing than both multilocus enzyme electrophoresis and
serotyping. It had similar discriminatory power to restriction endonuclease analysis, but the
results of PFGE were easier to interpret. When applied to 29 isolates collected from 4 farms
over periods of up to 8 years, 2 PFGE patterns were found on 3 farms, and a single pattern
on the other. In each case a new strain had apparently emerged as a variant of an original
parent strain. PFGE was found to be a powerful technique for investigating the molecular
epidemiology of swine dysentery outbreaks.