Comparison of the Diatheva STEC FLUO with BAX system kits for detection of O157:H7 and Non-O157 Shiga Toxin-Producing Escherichia coli (STEC) in ground beef and bean sprout samples using different enrichment protocols

Authors: ROTUNDO, LUCA - University Of Urbino; Fratamico, Pina; AMAGLIANI, GIULIA - University Of Urbino; CARLONI, ELISA - University Of Urbino; OMICCIOLI, ENRICA - Diatheva Srl; MAGNANI, MAURO - University Of Urbino

Submitted to: Journal of Food Analytical Methods
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/15/2018
Publication Date: 4/30/2018
Citation: Rotundo, L., Fratamico, P.M., Amagliani, G., Carloni, E., Omiccioli, E., Magnani, M. 2018. Comparison of the Diatheva STEC FLUO with BAX system kits for detection of O157:H7 and Non-O157 Shiga Toxin-Producing Escherichia coli (STEC) in ground beef and bean sprout samples using different enrichment protocols. Journal of Food Analytical Methods. https://doi.org/10.1007/s12161-018-1269-z.

Interpretive Summary: Food-borne pathogenic bacteria known as Shiga toxin-producing Escherichia coli (STEC) belonging to types O157:H7, O26, O103, O111, and O145 are responsible for a large portion of STEC infections worldwide. Cattle and other ruminants are reservoirs for these pathogens, thus food of bovine origin or food contaminated by cattle feces may be vehicles for infection with STEC. Therefore, these bacteria have been classified as adulterants in meat by the USDA Food Safety and Inspection Service (FSIS). Rapid and sensitive methods for detection of these pathogens in animal reservoirs and in food are needed to determine their prevalence and to ensure that food contaminated with STEC does not reach the consumer. The purpose of this study was to evaluate new commercially available real-time polymerase chain reaction- (amplification of specific segments of DNA of the pathogens) based kits to detect the target STEC in beef and bean sprouts and to compare the performance of this method to the protocol currently used by the FSIS for detection of these pathogens. The STEC were detected in ground beef and sprouts that were artificially contaminated with very low numbers of the bacteria using both the commercially available kits and the kits described in the FSIS Microbiology Laboratory Guidebook method. However, results showed that certain components in two of the four growth media that were evaluated hindered detection of the STEC, and thus, the choice of selective agents used for enrichment of STEC in foods must be carefully considered. In summary, the commercial method was rapid and simple and performed as well as the current method used for regulatory testing for STEC, and thus, it can be used for routine and rapid detection of STEC in beef and sprouts.

Technical Abstract: Aims: To assess the performance of the Diatheva STEC FLUO and BAX System real-time PCR assays for STEC detection (stx1/stx2 and eae target genes) and O-group identification in ground beef and bean sprout samples. Methods and Results: Ground beef and bean sprout samples were inoculated with approximately 10 CFU of the “top five” STEC (O157:H7, O26, O103, O111, and O145), enriched with different broths and incubation temperatures, and tested using the Diatheva and BAX assays. In ground beef, both molecular methods were able to detect the “top five” STEC, and lower Ct values were observed for the Diatheva kits compared to BAX System. The O111-contaminated samples gave negative results with both methods using mTSB+novobiocin for enrichment. In bean sprouts, both methods provided equivalent positive results, although detection was not possible using enrichment in mTSB+ACV. Conclusions: The Diatheva and BAX assays methods detected the “top five” STEC in ground beef and bean sprouts when inoculated at low levels. Both assays provided equivalent results in terms of performance and reliability. Significant and Impact of Study: The Diatheva kits are comparable to reference STEC-detection methods and could be used by the food industry to reliably detect the top five STEC.