Utilization of nylon membranes for the specific isolation of Escherichia coli O157 with DNA probes and checking for relationship to the shiga toxin Escherichia coli (STEC) group

A method for specific isolation of Escherichia coli strains of serotype O157 is given. DNA-hybridization technique by using DIG-labeled specific O157 PCR-amplificates as probes is the basis. These investigations can be used for the detection and isolation of shigatoxin-producing Escherichia coli (STEC) of this serotype in combination with other tests for detection of shigatoxin genes (stx). No background is seen by using 'DIG Easy Hyb' solution and Nylon membranes for colony-and plaque-hybridization (Roche Diagnostics Boehringer Mannheim). Dark brown spots (E. coli colonies) are visible on the membranes after staining. After comparing the membrane with the masterplate it is possible to isolate the colonies from the masterplate, respectively. It is necessary to make proof that the isolates possess the rfb-genes (verification of serotype O157) and the stx-genes (test for belonging to the STEC-group). Both tests could be done by using PCR. In case of positive results other virulence factors of the isolates can be detected.