USDA FSIS and FDA BAM Culture Methods BBL CHROMagar Salmonella Prepared Plated and Difco Dehydrated Culture Media

Abstract

BBL and Difco CHROMagar Salmonella (CS) was evaluated internally and externally for the recovery of Salmonella in raw chicken, raw ground beef, raw fish, lettuce, and shell eggs. The raw chicken and ground beef were processed according to the U.S. Department of Agriculture, Food Safety and Inspection Service reference methods. The raw fish, lettuce, and shell eggs were processed according to the U.S. Food and Drug Administration, Bacteriological Analytical Manual procedures. Only raw chicken was found to be naturally contaminated with Salmonella; all other matrixes were seeded with an appropriate dilution of organism to achieve fractionally positive results. Salmonella strains were permitted to equilibrate with the culture-negative matrixes for 48 h at 4 degrees C. Twenty 25 g samples of each food matrix plus 5 uninoculated samples were processed. CS prepared plates (CS PPM) and laboratory prepared plates from dehydrated culture media (CS DCM) were evaluated with the reference method media. A total of 16 positive cultures were obtained from the raw chicken samples, 17 in the raw ground beef, 18 in the raw fish and lettuce, and 11 in the shell eggs. A Chi-square analysis was performed on each of the food matrixes. BBL CS produced comparable results with the reference methods on all matrixes, resulting in a method agreement of 100% based on the Chi-square results. In testing known isolates the sensitivity and specificity was determined to be 94%. Specificity improved to 98% when tetrathionate broth enrichment was used. A negative- and false-positive rate of 6% was found with known isolates. No false negatives were found in testing the food matrixes. The performance of the CS prepared plate and laboratory prepared plate was identical.