Evaluation of BD BBL CHROMagar Staph aureus Medium Using AOAC and ISO Culture Methods

Abstract

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.