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.

The survival or clearance of the avian influenza virus (AIV) of subtype H7N2 in its chicken host was evaluated using experimentally infected specific pathogen free (SPF) chickens of different age groups. Birds of different ages were successfully infected with infectious doses ranging between 10(4.7) and 10(5.7) ELD50 per bird. In infected birds, the infective virus was undetectable usually by the third week following exposure. The infectivity or inactivation time of the H7N2 AIV in various environmental conditions was studied using chicken manure, heat, ethanol, pH, and disinfectants. The H7N2 AIV was effectively inactivated by field chicken manure in less than a week at an ambient temperature of 15-20 degrees C. At a pH 2, heating at 56 degrees C, and exposure to 70% ethanol or a specific disinfectant, the AIV infectivity was destroyed in less than 30 min.

Variability in the lipopolysaccharide (LPS) of the two most prevalent Salmonella serotypes causing food-borne salmonellosis was assessed using gas chromatography analysis of neutral sugars from 43 Salmonella enterica serovar Enteritidis (S. Enteritidis) and 20 Salmonella enterica serovar Typhimurium (S. Typhimurium) isolates. Four substantially different types of O-chain chemotypes were detected using cluster analysis of sugar compositions; these were low-molecular-mass (LMM) LPS, glucosylated LMM LPS, high-molecular-mass (HMM) LPS and glucosylated HMM LPS. Nineteen out of 20 S. Typhimurium isolates yielded glucosylated LMM. In contrast, S. Enteritidis produced a more diverse structure, which varied according to the source and history of the isolate: 45.5% of egg isolates yielded glucosylated HMM LPS; 100% of stored strains lacked glucosylation but retained chain length in some cases; and 83.3% of fresh isolates from the naturally infected house mouse Mus musculus produced glucosylated LMM LPS. A chain length determinant (wzz) mutant of S. Enteritidis produced a structure similar to that of S. Typhimurium and was used to define what constituted significant differences in structure using cluster analysis. Fine mapping of the S. Enteritidis chromosome by means of a two-restriction enzyme-ribotyping technique suggested that mouse isolates producing glucosylated LMM LPS were closely related to orally invasive strains obtained from eggs, and that stored strains were accumulating genetic changes that correlated with suppression of LPS O-chain glucosylation. These results suggest that the determination of LPS chemotype is a useful tool for epidemiological monitoring of S. Enteritidis, which displays an unusual degree of diversity in its LPS O-chain.

Eggs were cultured from four commercial chicken layer houses implicated in three human outbreaks of Salmonella enteritidis serotype enteritidis infection as part of the activities of the USDA-APHIS, VS, Salmonella enteritidis Task Force. Each house was part of a multiple in-line complex, ranging from three to seven houses. Houses were located on three separate farms, and each house contained between 50,000 and 80,000 chickens. S. enteritidis phage types 8, 13a, and 23 were isolated from samples taken from environmental and organ tissue samples, but only phage type 8 was cultured from eggs. Phage type 8 was isolated from humans in all three S. enteritidis outbreaks. Frequency estimates of contaminated eggs ranged from 0.03% to 0.90%.

Mice (Mus musculus) captured in henhouses were assessed for the presence of salmonellae in spleens. Of 621 and 526 spleens cultured during the first and second years of collection, 25.0 and 17.9%, respectively, were positive for Salmonella enterica serovar Enteritidis. Contaminated eggs were cultured from nine houses during the first year of sampling, and for eight of these houses, serovar Enteritidis was recovered from the spleens of mice. Rank sum statistical analysis of positive mouse spleens indicated that three overlapping bacterial populations were present. This pattern of infection was repeated when lipopolysaccharide (LPS) variants were used to infect chicks, and the worst infections were associated with isolates producing high-molecular-weight (HMW) LPS. Mouse isolates were capable of producing unprecedented amounts of HMW LPS as indicated by compositional analysis of six isolates that swarmed across 2% agar, which is a type of bacterial migration dependent upon production of HMW LPS. It is suggested that monitoring serovar Enteritidis cultured from the spleens of mice caught on farms will detect strains that are enhanced in their ability to contaminate eggs, in part because they are able to produce HMW LPS.