Collaborative evaluation of detection methods for Escherichia coli O157 : H7 from radish sprouts and ground beef

For the evaluation of plating and immunological methods applicable to the d etection of Escherichia coli O157:H7 from ground beef and radish sprouts, a collaborative study was conducted. It focused on a comparison of the effic iency of the plating and immunological methods using various plating agars and immune-kits in combination with enrichment in modified E. coli broth su pplemented with novobiocin (mEC + n), and using immunomagnetic separation. The plating media tested were sorbitol MacConkey agar (SMAC), SMAC suppleme nted with cefixime (0.05 mg/l) and potassium tellurite (2.5 mg/l) (CT-SMAC) , and agars containing beta-glucuronidase substrates such as BCM O157 and C HROMagar O157. The immune-kits used were Now E. coli, Path-Stick O157,VIP, EHEC-Tek ELISA System and Rapiblot E. coli O157. The 20 participating labor atories attempted to detect E. coli O157:H7 in 25 g chilled and frozen samp les of ground beef uninoculated and inoculated with E. coli O157:H7 at leve ls of 138.9 and 23.9 cfu/25 g, and in 25 g chilled and frozen samples of ra dish sprouts uninoculated and inoculated at levels of 20.4 and 1.7 cfu/25 g . E. coli O157:H7 was recovered well from ground beef by all of the methods except direct plating with SMAC. For radish sprouts, the IMS-plating metho ds with CT-SMAC, BCM O157 and CHROMagar O157 were most efficient at detecti ng E. coli O157:H7 in more than 90% of the chilled samples inoculated at th e level of 20.4 cfu/25 g. All the methods were less sensitive when applied to similar levels of E. coli O157:H7 in radish sprouts (20.4 cfu/25 g) comp ared with ground beef (23.9 cfu/25 g) especially if the sprouts were frozen . The sensitivity of the immune-kits appeared to be similar to the LMS-plat ing methods, but the specificity was lower. Based on the results, we recomm end the IMS-plating method using CT-SMAC and agars containing beta-glucuron idase substrate in combination with static enrichment incubation in mEC + n at 42 degrees C. (C) 1999 Elsevier Science B.V. All rights reserved.