The role of mice in the epizootiology of Salmonella enteritidis infection on chicken layer farms.

A microbiological survey of 10 mice-infested poultry farms was conducted to determine the role of mice in the epizootiology of S. enteritidis infection. Five of the farms were rated as clean of S. enteritidis and five as contaminated based on culture results of environmental samples for S. enteritidis. Of 2103 environmental samples and 715 mice and rats tested, 5.1% and 16.2%, respectively, were culture-positive for S. enteritidis. On contaminated farms, S. enteritidis was isolated from 24.0% of the mice and 7.5% of the environmental samples, which represented 75.3% of all Salmonella isolations from mice but only 18.0% of Salmonella isolations from environmental samples on these farms. S. enteritidis was not detected in mice on clean farms. Phage types 13a and 14b were the two most frequently isolated phage types from mice and environmental samples. Although only a single phage type was isolated from single free-standing poultry houses, multiple phage types were isolated from multi-house complexes. A bacterial count from the feces of one mouse yielded 2.3 x 10(5) S. enteritidis bacteria per fecal pellet. S. enteritidis persisted at least for 10 months in an infected mouse population.