Does your E. coli O157:H7 contain an F plasmid? M13 binds and infects E. coli cells through the F pilus. The genotype of TG1 is K-12 supE thi-1 Δ(lac-proAB) Δ(mcrB-hsdSM)5, (rK-mK-) F' [traD36 proAB+ lacIq lacZΔM15] . TG1 has an F' plasmid which allows for M13 infection.

E. coli O157:H7 Sakai contains a F-like plasmid, pO15.

This is what I found about pO157 pilus component:

"Downstream of the hemolysin operon, two adjacent ORFs showed ~50% similarity with 20 and 42 residues from different parts of a second E.coli regulator, PapX, that controls pilus production (P42193). The two ORFs (L7051 and L7052) represent parts of the gene separated by a frameshift. Pili are integral to the recognition and initial attachment of EHECs to the target cells. While there are no obvious pilus components encoded on pO157, two ORFs have some similarity to pilin-related proteins; one (L7081) shows 27% similarity over 67 residues to OrfQ (Q46527), of unidentified function in the fim operon of Bacteroides, and the second (L7024) shows 49% similarity to 43 amino acids in part of the fimbrial regulator FimB of E.coli (P04742)."

https://pdfs.semanticscholar.org/66fc/4ffd32b1bdb1757bb403fa4065400fe0a838.pdf

But I also read the M13 is able to infect several O157:H7 strains. Probably this is not the case.

Thanks a lot for your answer!