These four chemical combinations were tested for their antimicrobial effects on E. coli O26:H11 and E. coli O111:NM in water containing large amounts of rumen content (10:1 [vol/wt]). The results revealed that the same three combinations, A, B, and C, had similar antimicrobial activities (ca. 5-log CFU/ml reduction within 20 min at 21°C) against E. coli O26:H11 (Table (Table2)2) and E. coli O111:NM, except for treatment B, which required 30 min for a 5-log CFU/ml reduction (Table (Table3).3). Combination D reduced E. coli O26:H11 and E. coli O111:NM populations within 20 min by 3.3 and 3.0 log CFU/ml, respectively (Tables (Tables22 and and33).