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Collaborative evaluation of detection methods for Escherichia coli O157:H7 from
radish sprouts and ground beef.
Int J Food Microbiol 1999 Jan 12;46(1):27-36
Onoue Y, Konuma H, Nakagawa H, Hara-Kudo Y, Fujita T, Kumagai S.
Kanagawa Prefectural Public Health Laboratory, Yokohama, Japan.
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.
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