Detection of freeze-injured Escherichia coli O157:H7 cells from foods by resuscitation prior to selective enrichment

We tried to detect Escherichia coli O157:H7 in food samples artificially contaminated with freeze-injured E. coli O157:H7 using an enrichment method with modified EC broth supplemented with novobiocin (mEC+n). When the samples were cultured for enrichment immediately after inoculation of freeze-injured cells, E. coli O157:H7 was not detected in 13 out of 18 samples. However, allowing the food samples to stand for 3 h at room temperature prior to enrichment in mEC+n remarkably improved recovery of E. coli O157:H7 except for some acidic foods. E. coli O157:H7 was detected in the acidic foods by introducing a resuscitation step of 3-h of incubation in a non-selective broth at room temperature prior to enrichment with mEC+n.