The inhibitory effect of calcinated calcium on the growth of Escherichia coli O157:H7 during fresh radish (Raphanus sativus L.) sprout production was studied. It was revealed that the addition of 0.4% (wt/vol) calcinated calcium into radish sprouting medium which was artificially contaminated with E. coli O157:H7 (3.0 to 3.2 log CFU/ml) completely inhibited the growth or inactivated the microorganism. When radish seed extract was used instead of radish sprout production, the same extent of growth inhibition or inactivation was observed with much lower amounts (0.07%) of calcinated calcium under similar experimental conditions. The findings suggested that calcinated calcium may be useful to control E. coli O157:H7 contamination during the production of radish sprouts.

ABSTRACT. To develop a rapid and specific method to detect and/or identify enterohemorrhagic Escherichia coli O157:H7, two mouse monoclonal antibodies (MAbs) were prepared. Specificities of these two MAbs (1D9 and 3E8) were determined by flow cytometry method (FCM). MAbs 3E8 and 1D9 were found to react with E. coli O157:H7, Citrobacter freundii and Salmonella group N (O:30), but not with Escherichia hermannii. With a mixture containing strains of E. coli O157:H7 and E. coli O6:H1, two different peaks appeared in FCM with MAbs, whereas a single peak appeared with polyclonal rabbit antiserum. From these findings, FCM with MAb is suggested to be a rapid, specific, and useful method to detect and identify strain(s) of E. coli O157:H7 in food ingredients. -KEY WORDS: Escherichia coli, FCM, O157.

To detect low concentrations of enterohaemorrhagic Escherichia coli O157:H7 rapidly, flow cytometry (FCM) was carried out with specific IgG-sensitized latex beads (IgG-Lx). It was found that test samples for FCM can be prepared for much shorter periods by culturing E. coli O157:H7 in trypto-soya broth at 42 degrees C and by treatment with 0.5% formalin at 37 degrees C. FCM with IgG-Lx performed with E. coli O157:H7 prepared by such a procedure revealed that the lowest number of E. coli O157:H7 prepared in pure culture detected by FCM was 10(3)/ml. Because similar findings have already been reported by FCM with immunomagnetic beads, FCM with IgG-Lx is also suggested to be a valuable technique to detect low numbers of E. coli O157:H7 rapidly in food stuffs.

Direct detection of E. coli O157 by flow cytometry (FCM) was performed using heattreated E. coli O157 and FITC-labeled anti-E. coli O157 IgG. The flow cytogram which was obtained within 30 minutes revealed an obvious difference between E. coli O157 treated with and that untreated with FITC-labeled anti-E. coli O157 IgG. There was also a clear difference between E. coli O157 and other strains of E. coli than E. coli O157 in reaction with FITC-labeled IgG.Among twelve other strains of E. coli tested, six strains exhibited agglutination titers ranging from 1 to 4. The same six strains also gave weaklypositive results in FCM. It is therefore possible to count the numbers of E. coli bearingthe O157 antigen by using FCM.