ABSTRACT: The antimicrobial activity of origanum oil (OG) was determined against Salmonella Typhimurium and E. coli O157:H7. The efficacy of catfish gelatin coating containing selected concentrations of OG (0.5%, 1.0%, and 2.0%, v/v) was also investigated in catfish flesh irradiated, inoculated with both bacteria, and stored at selected temperatures. The antimicrobial activity of catfish gelatin coating was determined by cell counts during storage at 4 and 10 °C for 12 d. The color properties of catfish flesh coated with catfish gelatin containing OG were also measured. In the media, the inhibitory effects of OG against S. Typhimurium were greater than the inhibition effects against E. coli O157:H7, exhibiting complete inhibition against S. Typhimurium at the concentration greater than 0.5% (v/v). The incorporation of OG into catfish gelatin coating also inhibited both S. Typhimurium and E. coli O157:H7 in catfish flesh stored at 4 °C. The reduction of S. Typhimurium counts by gelatin coating containing 0%, 0.5%, 1%, 2% (v/v) OG were 0.58, 0.73, 1.16, and 1.76 log CFU/g, respectively, exhibiting the greatest effect at 2% (v/v) OG (P < 0.05). During storage at 10 °C, the reduction of S. Typhimurium counts by catfish gelatin coatings with 0%, 0.5%, 1%, and 2 % (v/v) OG were 0.67, 0.91, 1.32, and 2.05 log CFU/g, respectively. The incorporation of OG into catfish gelatin coating exhibited greater antimicrobial activity against S. Typhimurium than against E. coli O157:H7 at both temperatures. The lightness and yellowness of catfish flesh was not altered; however, the redness of catfish gelatin was decreased by catfish gelatin coating containing OG.