CONDITIONS AFFECTING AUTOINDUCER-2-BASED QUORUM-SENSING OF ESCHERICHIA COLI O157:H7 ON FRESH BEEF Y. YOON and J.N. SOFOS 1 Center for Meat Safety & Quality Department of Animal Sciences 1171 Campus Delivery Colorado State University Fort Collins, CO 80523 Accepted for Publication November 26, 2007 ABSTRACT This study evaluated whether inoculated (none, 1, 5 log colony-forming units [cfu]/cm 2 ) Escherichia coli O157:H7 would result in detection of auto- inducer (AI)-2-like activity on beef. Inoculated fresh beef, containing low (LNB) or high (HNB) initial levels of natural flora, was analyzed for bacterial populations and AI-2-like activity during aerobic or vacuum-packaged storage (4, 10, 25C). As expected, no growth of E. coli O157:H7 was detected at 4C, while at 10C, growth was detected only on LNB samples stored aero- bically; AI-2-like activity was minimal (P  0.05) at both temperatures. E. coli O157:H7 showed more growth in LNB than HNB, and in aerobically than vacuum-packaged samples inoculated with 1 log cfu/cm 2 of the pathogen during storage at 25C. AI-2-like activity was generally higher in LNB than HNB samples stored aerobically at 25C, while no significant AI-2-like activity was detected in samples stored in vacuum packages. The results indicated that E. coli O157:H7 may exhibit AI-2-like activity on aerobically stored beef in the presence of lower initial levels of natural flora, and at temperatures allowing prolific growth of the pathogen. Thus, AI-2-based quorum-sensing of E. coli O157:H7 may not be of importance in beef stored at low temperatures. PRACTICAL APPLICATIONS This study presents evidence that Escherichia coli O157:H7 showed autoinducer (AI)-2 activity and involved in quorum-sensing on fresh beef 1 Corresponding author. TEL: 970-491-7703; FAX: 970-491-0278; EMAIL: John.Sofos@ colostate.edu Journal of Food Safety 28 (2008) 587–600. All Rights Reserved. © 2008, The Author(s) Journal compilation © 2008, Wiley Periodicals, Inc. 587