ABSTRACTThe effects of chlorine against 2 strains ofE. coliattached to the surface of beef carcass tissue (BCT) were examined using a model carcass washer. Lean and adipose BCT with approximately 5 log10CFU/cm2E. colibacteria were spray‐treated with water and sodium hypochlorite (NaOCl) to give chlorine concentrations of 50, 100, 250, 500, or 800ppm, incubated for 24 h, 4C, andE. colipopulations enumerated. Spray treatments with water did significantly (P<0.05) reduce the bacterial populations of either organism attached to lean or adipose BCT, as compared to populations of controls; however, reductions were less than 0.60 log10CFU/cm2.Treatments with 500 and 800 ppm chlorine againstE. coliATCC 25922 attached to BCT resulted in the greatest reductions of 1.22 and 1.28 log10CFU/cm2,respectively. At 800 ppm chlorine, E. coliO157:H7 ATCC 43895 attached to BCT was reduced by 1.04 log10CFU/cm2,whereas spray treatments with 50, 100, 250, and 500 ppm chlorine resulted in reductions of<1 log10CFU/cm2.Spray treatments with chlorine from sodium hypochlorite solutions reduced populations ofE. coli,however, these reductions were not sufficient to completely inactivate the bacteria attached to red mea