DEVELOPMENT OF A SELECTIVE PLATING TECHNIQUE FOR THE RECOVERY OF ESCHERICHIA-COLI O157-H7 AFTER HEAT-STRESS

The use of Sorbitol MacConkey Agar supplemented with 4-methylumbellife ryl beta-D-glucuronide (MSMA), which is commonly used in the isolation of Escherichia coli O157:H7, has been shown to perform poorly when st ressed cells of the pathogen are present. The incorporation of a resus citation period (2 h at 25 degrees C) on Trypticase Soy Agar (TSA) bef ore overlay with MSMA was found to significantly (P less than or equal to 0.01) improve recovery of heat-stressed (52 degrees C/60 min) cell s. Maximal recovery was, however, obtained by adding catalase (1000 U) to the TSA before overlaying with MSMA. This recovery protocol was sh own not to result in the loss of the major known virulence factors of E. roll O157:H7 (genes encoding eae, VT1 and VT2).