FIG. 2.

Production of stx₂ RNA, Stx2, and phage from STEC strains 1:361 and 1:361ΔQ-p_R′. (A) Measurement by Northern blotting of stx mRNA levels. Total RNA was prepared from 3-h cultures of 1:361 and 1:361ΔQ-p_R′ grown with (+) or without (−) 0.5 μg of mitomycin C per ml. Six micrograms of RNA was run on a 1% agarose gel, transferred to a nylon membrane, and then probed with a ³²P-labeled Stx2-encoding sequence riboprobe. (B) Total Stx2 was measured from the same cultures used in the Northern blot, using a previously described ELISA (14). Values with standard deviations from three independent measurements are shown. (C) Phage titers were determined using E. coli C600 as the indicator strain (3). This procedure leaves uncounted mutant phage producing very low bursts.