Comparison of the RAPID-B super( registered ) flow cytometer and the BAX super( registered ) system for the detection of non-O157 shiga toxin-producing Escherichia coli (STEC) in beef products

The beef industry continues to be interested in reliable rapid detection technologies for shiga toxin-producing Escherichia coli (STEC). Current rapid technologies require several hours of pre-enrichment and additional time on the rapid technology instrument. A flow cytometer-based system (RAPID-B super( registered )) has been shown to improve the turn-around for results with a more rapid pre-enrichment requiring only 6.5 h pre-enrichment for a 25 g and 8.5 h for a 375 g sample, followed by an additional 30 min time to achieve final results using the screening technology. The purpose of this study was to validate the RAPID-B super( registered ) technology for non-O157 STEC detection as compared to the USDA-FSIS reference method which utilizes the BAX super( registered ) system. A total of 180 STEC isolates from various sources and 20 non-STEC strains were used to evaluate specificity and sensitivity using the RAPID-B super( registered ) flow cytometer. Also, three different weights (25, 325 and 375 g) of beef trim and ground beef samples were spiked with each STEC to verify detection sensitivity of BAX super( registered ) system and RAPID-B super( registered ) flow cytometer. For both methods, samples were confirmed by culturing using the USDA-FSIS reference method regardless of the screening result. The RAPID-B super( registered ) flow cytometer showed that 180 isolates were all positive and the 20 non-STEC strains were all negative. For spiked beef samples, overall detection sensitivity was the same for both the BAX super( registered ) system and RAPID-B super( registered ) flow cytometer. When detection sensitivity was based on sample weight, there was no differences in 25 and 375 g samples between RAPID-B super( registered ) flow cytometer and USDA-FSIS reference method. The RAPID-B super( registered ) system yielded the same sensitivity as the reference method with a decrease of over 10 h of pre-enrichment time and 3 h of rapid screening detection time. In conclusion, the RAPID-B super( registered ) flow cytometer based on whole cell detection generated similar results as BAX super( registered ) system therefore the RAPID-B super( registered ) flow cytometer system could be a valuable rapid method for the detection of non-O157 STEC in beef products.