Screening facultative sheep‐rumen bacteria which inhibit growth of Escherichia coliproduced 11 strains of Pseudomonas aeruginosa. The isolates showed three different pulsed‐field gel electrophoresis patterns and strains from different sheep produced pyocins that varied in strain specificity. Representative strains were resistant to ampicillin, methicillin, erythromycin, fusidic acid and augmentin, but not to tetracycline or nalidixic acid. Tested strains attached in large numbers to cultured rumen epithelial cells, potentially providing a means of survival in this ecosystem.