After incubation for 18 h at 37C the densely overgrown streak was chloroform-inactivated using a Pasteur pipette to form a thin film covering the whole streak of bacteria. The inhibitory activity was determined qualitatively by applying 10 ll of a standardized 0Æ85% NaCl suspension (McFarland Standard 1) of tested pathogen or indicator strain (E. coli N54) perpendicularly to the chloroform-inactivated producing strain.