Utilization of Nylon membranes for the specific isolation of Escherichia coli O157 by using DNA-probes and checking the isolates of belonging to the group of shigatoxin-producing Escherichia coli (STEC)

A method for specific isolation of Escherichia coli strains of serotype O15 7 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 (S TEC) of this serotype in combination with other tests for detection of shig atoxin genes (stx). No background is seen by using 'DIG Easy Hyb' solution and Nylon membranes for colony-and plaque-hybridization (Roche Diagnostics Boechringer Mannheim ). Dark blown spots (E. coli colonies) are visible on the membranes after s taining. 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 (veri fication of serotype O157) and the stx-genes (test for belonging to the STE C-group). Both tests could be done by using PCR. In case of positive result s other virulence factors of the isolates can be detected.