Reliability of the modified semi-solid Rappaport-Vassiliadis agar and the modified 1-2 test registered system for detection of Salmonella in poultry feeds

The sensitivity of two screening methods for the rapid detection of Salmonella in naturally contaminated poultry feeds was compared to a standard cultural procedure. Of the 1,197 samples of poultry feeds and poultry feed supplements tested, 104 (8.7%) were found to be contaminated with Salmonella by all methods combined. Data from the modified semi-solid Rappaport-Vassiliadis agar (MSRV) /standard cultural procedure comparison showed equivalence of these two methods; 69 of 700 samples analyzed were positive for Salmonella by both methods combined. The false negative rate for the MSRV was 1.0% and for the standard cultural method 1.14%. Comparing the modified 1-2 Test and the standard cultural method, the false negative rate was equal at 0.85%, where 85 of 1,061 samples were Salmonella positive by both methods combined. Analysis of 645 samples (56 Salmonella positive) by the three test procedures yielded false negative rates of 1.24% (standard cultural), 0.93% (MSRV) and 1.09% (Modified 1-2 Tests). The false positive rates for the three methods were: standard cultural - 0.08%; MSRV - 0.86%; modified 1-2 Test - 1.04%. The agreement between the three methods of analysis was satisfactory overall, indicating that both the MSRV and the Modified 1-2 Test procedures are reliable methods for Salmonella analysis of poultry feeds and poultry feed supplements.