Salmonella collected from nest run cart shelves in commercial shell egg processing facilities

Abstract

Salmonella, a member of the bacterial family Enterobacteriaceae, may be recovered from foods and processing facilities. High levels of Enterobacteriaceae in the processing plant environment can be an indication of inadequate sanitation. This experiment was designed to determine if nest run egg carts serve as reservoirs for Salmonella. Eggs that are produced by hens not housed in buildings connected to the processing plant are referred to as nest run. Many of these eggs are transported to a central processing facility before they are washed, graded, and packed. Two plants in the Southeastern United States were sampled; one was a mixed operation and the other was an off-line operation. On each of 3 visits, 5 shelves on each of 5 carts were sampled (n = 25/visit). A 12 × 12 cm area on each shelf was swabbed with a sterile gauze pad moistened with PBS and transported on ice back to the laboratory. Each swab was preenriched in buffered peptone at 37°C for 24 h, selectively enriched using TT and Rappaport-Vassiliadis broth at 42°C overnight, then plated onto brilliant green sulfa and XLT-4 incubated at 37°C for 24 h. Presumptive colonies were transferred to lysine iron agar and triple sugar iron slants for 24 h at 37°C. Isolates with presumptive reactions were confirmed using commercial polyclonal antisera. After initial confirmation, serogrouping was performed using commercial antisera. Mixed-operation swab samples were 12% positive for Salmonella, whereas off-line samples were 36% positive for Salmonella; isolates were confirmed as serogroups B, C1, and C2. Kauffman-White serotyping was performed by a contract laboratory. Serotypes (n = 30) recovered were Anatum, Heidelberg, Infantis, Kentucky, Mbandanka, and Typhimurium. This work demonstrated that nest run egg carts may serve as reservoirs for Salmonella in the shell egg processing environment.