Comparison of the immunomagnetic separation method (IMS) with an automated immunoconcentration (VIDAS-ICE) system for detecting Escherichia coli O157:H7 in bovine raw milk and unpasteurized cream

In order to compar two commercially available immunoseparation/immunoconcentration methods for the isolation of Escherichia coli O157:H7 from food enrichments, a total of 80 dairy samples (40 bovine raw milk samples and 40 unpasteurized cream samples) were tested. The samples were collected in the Parmesancheese area, Parma province (northern Italy), from 9 cheese factories. The IMS requires a 24 h enrichment in m-TSB+acriflavin and after immunoseparation the Dynabeads®-bacteria complexes are plated onto CT-SMACTheVIDAS-ICE method needs a double enrichment, 6 h in m-TSB+acriflavin followed by 18 h in CT-MacConkey broth, and after automated immunoconcentration the samples are streaked onto O157:H7 ID chromogen medium. Even if no colonies of E. coli O157:H7 were isolated from the dairy samples, the IMS technique was laborious compared to the VIDAS ICE method. Moreover, confirmation of suspect colonies grown on CT-SMAC was time-consuming, due to the higher number of sorbitol-negative colonies to be tested compared to the lower number of green colonies grown on O157:H7 ID (433 vs. 153).