Yeast extract

Bacterial strains, bacteriophages and plasmids used in this study are listed in Table 3. The E. coli O157:H7 C7927 bacterial strain was used for the cultivation of phage ΦV1032 (link). Homologous recombination was carried out in a lysogenic strain E. coli O157:H7 C7927 (ΦV10) bearing the lambda Red expression plasmid pKD46. For the construction of ΦV10 reporter phage, bacterial strains were grown in Luria-Bertani (LB) broth (Difco Laboratories, MI) or LB agar plates supplemented with antibiotics as needed [ampicillin (Ap), 100 μg ml⁻¹; kanamycin (Kan), 50 μg ml⁻¹ (Sigma-Aldrich, MO)]. Salt-Optimized Carbon broth medium (SOC) (Clontech Laboratories, Inc, CA) was used for recovery of cells after electroporation. Modified tryptone soya broth (Oxoid Ltd., UK) containing 1% casamino acids (VWR International, PA) with novobiocin (Sigma-Aldrich, MO) of 8 mg l⁻¹ (mTSB + n) was used for ground beef enrichment as specified by the USDA-FSIS protocol33 34 . Cell dilutions were done in phosphate buffered saline (PBS) (8 mM Na₂HPO₄, 6 mM NaH₂PO_4, 145 mM NaCl, pH7.6). Phage buffer (50 mM Tris, 100 mM MgCl₂, pH7.6) was used to dilute and preserve the phage stock. LB Top agar (1% (wt/vol) tryptone (Becton Dickinson, NJ), 1% (wt/vol) NaCl (Macron, PA), 0.5% (wt/vol) yeast extract (Hardy Diagnostics, CA) and 0.6% (wt/vol) agar (Alfa Aesar, MA)) was used for the overlay plaque assay.