#06-185

Complete

Date Full Report Received

02/17/2010

Date Abstract Report Received

02/17/2010

Investigation

Institution:
Primary Investigator:

Salmonella control requires practical means to reliably test for shedding of the organism. Fecal samples offer the potential to sample on farms or at slaughter plants. However, methods to culture Salmonella are time consuming and require immediate processing. This means that samples must either be processed at the site, or transported immediately to an appropriate laboratory. The objective of this study was to develop reliable methods to freeze samples so that the logistics of sampling could be improved in future studies or other applications. We inoculated feces from growing pigs with strains of Salmonella previous derived from healthy pigs at slaughter. Freezing samples decreased the number of Salmonella recovered using conventional microbiologic technique. Addition of glycerol reliably increased the recovery, that is, decreased the loss of culturable Salmonella due to freezing. The addition of sterile skim milk, Buffered Peptone Water and LB Broth also enhanced recovery, although not as consistently as glycerol. Extending samples with 20% glycerol was reliably helpful; 40% glycerol was detrimental in some experiments. Adding a water based diluent (Phosphate Buffered Saline) before freezing reduced Salmonella recovery; this effect was lessened if glycerin was also added. The findings of this project suggest that for certain applications where financial or practical constraints make storage of samples before testing desirable, freezing with the addition of 20% glycerol and 20% skim milk should increase recovery of Salmonella.