BBL CHROMagar Staph aureus (CSA) medium was evaluated internally and externally for the isolation and enumeration of Staphylococcus aureus in cooked roast beef, smoked salmon, and shell eggs. All food matrixes were processed according to the AOAC Official Method 975.55 and ISO 6888-1:1999. Bacterial counts of S. aureus were compared on CSA to the reference media, Baird-Parker, at low, medium, and high contamination levels. Colony counts were converted to log10 for statistical analysis. Based on the paired t-test and one-way analysis of variance, no statistical difference was noted with the CSA method compared to the AOAC Official Method for the recovery of S. aureus for all food types and contamination levels. Compared to the ISO reference method, no statistical difference was found with the CSA method for any food type or contamination level, with the exception of low-level smoked salmon. A statistical difference was seen in the internal testing with the low-level contaminated smoked salmon where CSA recovered more colonies. The external testing showed no statistical difference with smoked salmon at the low level. The correlation coefficients ranged from 92.6 to 99.4, demonstrating good correlation for overall levels in all food types and methods. The sensitivity and specificity of the CSA method using known isolates was 100. The results of this study demonstrate that CSA is an effective medium for the isolation, enumeration, and presumptive identification of S. aureus in cooked roast beef, smoked salmon, and shell eggs in 24 h using ISO and AOAC official methods.

BBL CHROMagar Listeria Media (CL) was evaluated for detection of Listeria monocytogenes in raw ground beef, smoked salmon, lettuce, and Brie cheese. The recovery of L. monocytogenes on CL was compared to the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM), U.S. Department of Agriculture (USDA) Food Safety and Inspection Service (FSIS), AOAC, and International Organization for Standardization (ISO) reference-plated media using the recommended pre-enrichments and selective enrichments. Of the 265 food samples tested, 140 were tested using BAM, USDA, or AOAC methods and 125 were tested using ISO methods. CL produced comparable results with the reference methods on all matrixes with a sensitivity of 99.3 and a specificity of 100. No false negatives were found in testing the food matrixes. There was no statistical difference in recovery based on Chi-square analysis. Known isolates were evaluated, and CL had a sensitivity and specificity of 100. The results of this study demonstrate that CL is an effective medium for the recovery and detection of L. monocytogenes in raw ground beef, smoked salmon, lettuce, and Brie cheese using FDA BAM, USDA FSIS, AOAC, and ISO culture methods.