Competitive exclusion of Salmonella enteritidis by Salmonella gallinarum in poultry

Salmonella Enteritidis emerged as a major egg-associated pathogen in the la te 20th century. Epidemiologic data from England, Wales, and the United Sta tes indicate that S. Enteritidis filled the ecologic niche vacated by eradi cation of S. Gallinarum from poultry, leading to an epidemic increase in hu man infections. We tested this hypothesis by retrospective analysis of epid emiologic surveys in Germany and demonstrated that the number of human S. E nteritidis cases is inversely related to the prevalence of S. Gallinarum in poultry. Mathematical models combining, epidemiology with population biolo gy suggest that S. Gallinarum competitively excluded S. Enteritidis from po ultry flocks early in the 20th century.