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 detection of Escherichia coli O157:H7 from ground beef and radish sprouts, a collaborative study was conducted. It focused on a comparison of the efficiency of the plating and immunological methods using various plating agars and immuno-kits in combination with enrichment in modified E. coli broth supplemented with novobiocin (mEC + n), and using immunomagnetic separation. The plating media tested were sorbitol MacConkey agar (SMAC), SMAC supplemented 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 CHROMagar O157. The immuno-kits used were Now E. coli, Path-Stick O157, VIP, EHEC-Tek ELISA System and Rapiblot E. coli O157. The 20 participating laboratories attempted to detect E. coli O157:H7 in 25 g chilled and frozen samples of ground beef uninoculated and inoculated with E. coli O157:H7 at levels of 138.9 and 23.9 cfu/25 g, and in 25 g chilled and frozen samples of radish 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 methods with CT-SMAC, BCM O157 and CHROMagar O157 were most efficient at detecting E. coli O157:H7 in more than 90% of the chilled samples inoculated at the 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) compared with ground beef (23.9 cfu/25 g) especially if the sprouts were frozen. The sensitivity of the immuno-kits appeared to be similar to the IMS-plating methods, but the specificity was lower. Based on the results, we recommend the IMS-plating method using CT-SMAC and agars containing beta-glucuronidase substrate in combination with static enrichment incubation in mEC + n at 42 degrees C.
Kanagawa Prefectural Public Health Laboratory, Yokohama, Japan.
Y
Y
Onoue
H
H
Konuma
H
H
Nakagawa
Y
Y
Hara-Kudo
T
T
Fujita
S
S
Kumagai
D000818:Animals; D002417:Cattle; D015169:Colony Count, Microbial; D004797:Enzyme-Linked Immunosorbent Assay; D019453:Escherichia coli O157 / Q000302:isolation & purification*; D005516:Food Microbiology; D006801:Humans; D018189:Immunomagnetic Separation; D007841:Latex Fixation Tests; D008460:Meat / Q000382:microbiology*; D018520:Plant Shoots / Q000382:microbiology*; D012680:Sensitivity and Specificity; D014675:Vegetables / Q000382:microbiology*