A Comparison of Sample Weight and Culture Methods for the Detection of Salmonella in Pig Feces

Abstract

Five protocols were compared to determine the combined effects of different sample weights and culture methods for the recovery of Salmonella from 310 pig cecal samples taken in abattoirs as part of the Canadian Integrated Program for Antimicrobial Resistance Surveillance. Sample weights evaluated were 1 and 10 g. Culture methods used with each sample weight were modified semisolid Rappaport-Vassiliadis agar (MSRV) and brilliant green agar with sulfa and novobiocin (BGSN) and xylose-lysine-tergitol-4 agar (XLT4). A preliminary sample preparation step in saline was also evaluated using a 10-g sample and MSRV. The Salmonella recovery rate varied from 20% for the saline MSRV 10-g protocol to 32% for the MSRV 10-g and the BGSN-XLT4 10-g protocols. A good agreement (κ > 0.8) was observed between pairs of protocols except whenever the saline MSRV 10-g and the MSRV 1-g protocols were compared. Larger samples (10 g) yielded higher detection of Salmonella than 1-g samples for the MSRV protocol (32 versus 25%), whereas the differences were not statistically significant for the BGSN-XLT4 protocols. Protocols using the BGSN-XLT4 agar yielded higher detection rates of Salmonella compared with MSRV with 1-g samples (30 versus 25%), whereas it was equivalent with 10-g samples. Considering a greater recovery rate, the ease of use, and a better time and resource efficiency, the MSRV 10-g protocol was therefore adopted by the Canadian Integrated Program for Antimicrobial Resistance Surveillance.