ON-FARM MONITORING OF MOUSE-INVASIVE SALMONELLA ENTERICA VAR ENTERITIDIS AND A MODEL FOR ITS ASSOCIATION WITH THE PRODUCTION OF CONTAMINATED EGGS

Authors: PETTER, JEAN; HENZLER, DAVID - USDA,FSIS; RAHMAN, MAHBUBUR - U. OF GEORGIA; CARLSON, RUSSELL - U. OF GEORGIA

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/27/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: This research produced a epidemiological model for Salmonella enterica var. Enteritidis (Enteritidis) infections in naturally infected mice that was confirmed in experimentally infected chicks. Evidence strongly suggests that there are three major populations of Enteritidis and only one appears to be associated with significant virulence, which is defined by this research approach as recovery from spleens after intraperitoneal infection of chicks. Previous research had shown that the virulent population was associated with the ability to contaminate eggs. The structure of the major outer membrane carbohydrate, lipopolysaccharide (LPS), was shown to be useful for identifying each of the three populations. Further analysis indicated that field isolates are capable of producing LPS structures that are rarely seen in the laboratory and are detectable when strains swarm across agar surfaces. This research supports that LPS structure is a major determinant of the ability of Enteritidis to be virulent and to contaminate eggs. Vaccination of flocks in production appeared to be associated with lowered recovery of Enteritidis from eggs even when the environment and spleens of mice yielded Enteritidis as compared to unvaccinated flocks. This work is important because it shows that mice are important reservoirs of organ- invasive Enteritidis and because it clarifies the biochemical nature of outer membrane structures that contribute to organ invasiveness.

Technical Abstract: Mice (Mus muscalis) captured in hen houses were assessed for the presence of salmonellae in spleens. Of 621 and 526 spleens cultured during a first and second year of collection, 25.0% and 17.9% were positive for Salmonella enterica var. Enteritidis. Var. Typhimurium was isolated from 1.3% of total spleens cultured, while no other salmonellae were obtained. Contaminated eggs were cultured from nine houses during the first year of sampling, and for eight of these houses, Enteritidis was recovered from the spleens of mice. Environmental sampling was less reliable at detecting houses producing contaminated eggs than organ culturing. Rank statistical analysis of positive batch data from individual farms indicated that three overlapping bacterial populations were present in the data set of positive spleens, and that similar populations were again identified using characterized lipopolysaccharide variants for infection of chicks. These data support that high-molecular-weight smooth lipopolysaccharide is associated with organ invasion, egg contamination and the potential for transmission of Enteritidis to people.