Lineage II Escherichia coli O157:H7: genomes, prophages, colicins, and the absence of detectable Stx2.

Lineage II Escherichia coli O157:H7 strains show no detectable Stx2 by Western blot, despite stx2 transcription in 2 of 3 mitomycin C–induced lytic strains.

• Why it matters: This addresses whether lineage II EHEC can produce functional phage and detectable Stx2, a key toxin linked to disease, and clarifies why lineage II persists mainly in bovine and farm environments.
• What they did: Three lineage II genomes (FRIK2069, FRIK2455, FRIK2533) were sequenced and compared, and 11 lineage II strains from the United States were tested for functional phage and Stx2 after mitomycin C treatment.
• The result: Three of 11 strains underwent delayed lysis after 24 h, stx2 transcription occurred in 2 of those, but Stx2 was not detected in any lytic or non-lytic lineage II strain; eight lineage II lysates inhibited E. coli MG1655 via colicins.