Temporal changes in the population genetics of Salmonella pullorum

Salmonella pullorum is the cause of pullorum disease, which is characterize d by white diarrhea and a high mortality rate in poultry. During the 1990s, the serologic "pullorum" test has occasionally failed to detect infected b irds during the early stage of disease. To determine if any recent genetic changes have taken place in S. pullorum to account for poor seroconversion sometimes observed in infected flocks, S. pullorum from 1930s outbreaks and strains isolated prior to the 1980s were typed by random amplified polymor phic DNA (RAPD). Of 40 S. pullorum isolates typed by this method, eight dis tinct DNA patterns were identified with one of three RAPD polymerase chain reaction primers. Sixty-two percent of S. pullorum isolates shared the same RAPD DNA pattern, and a major proportion of these strains were from recent flock infections. The RAPD patterns for S. pullorum were clearly distinct from the avian Salmonella group B isolates included in this analysis. The d istribution of Salmonella virulence genes among avian Salmonella isolates w as also examined. Eighty-five percent of the S. pullorum isolates had both the virulence plasmid gene, spvB, and the invasion gene, invA, with the sam e percentage positive for the Salmonella enteriditis fimbrial gene, sef: Ho wever, significant variability was observed among S. pullorum in their abil ity to invade avian epithelial cells, despite the presence of the Salmonell a invasion gene in these isolates.