Escherichia coli collection of reference (ECOR) is a standard collection of 72 wild-type E. coli strains that represent natural E. coli populations found in various environments. Although these strains are widely used in experiments investigating the physiology and behavior of wild-type E. coli, their genetic features including accessory DNA have not been sufficiently studied. In this study, we surveyed for the presence of lysogenic phages in each ECOR strain under both inducing and non-inducing conditions. We found that 34 strains could produce plaque-forming phages; among them, 14 strains were newly discovered to harbor lysogenic phages capable of entering the lytic cycle. We isolated a new phage (designated as “MSU52-L1”) from the ECOR52 strain and identified it as a P22/lambda-like phage with homology to known phages, such as CUS-3, HK620, and HK140.