ABSTRACT:Lactose‐negativeEscherichia coilfrom cattle feces appeared as yellow, atypical colonies on m‐FC medium plates with water samples from rangeland streams. The lactose‐negativeE. coilmay impact stream water quality analyses if infrequent samples are collected; are less antibiotic resistant than the lactose‐positiveE. coiliisolated from rangeland streams; and are colicinogenic toward all the laboratory strains ofE. coilexamined and toward 61 percent of the lactose‐positiveE. coilrangeland‐stream isolates that were tested. This latter result could explain the potentially low degree of antibiotic resistance transfer from lactose‐positive to lactose‐negativeE. coil. In addition, the colicinogenicity of the lactose‐negativeE. coilmay interfere with microbiological water quality analyses that depend upon lactose fernientations with mixed populat
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