FLUORESCENT-ANTIBODIES APPLIED TO DIRECT EPIFLUORESCENT FILTER TECHNIQUE FOR MICROSCOPIC ENUMERATION OF ESCHERICHIA-COLI 0157-H7 IN MILK AND JUICE

In a modification of the direct epifluorescent filter technique (DEFT) , direct fluorescent antibody staining was used for the rapid (<1 h), specific enumeration of foodborne Escherichia coli 0157:H7 by epifluor escence microscopy. Cell counts obtained by this method (Ab-DEFT) corr elated well with DEFt counts obtained by acridine orange staining and with viable plate counts ranging from 10(8) to 10(1) cells per ml for pure cultures in buffer. Ab-DEFT also was effective for counting E. co li 0157:H7 cells inoculated into milk and juice; the sensitivity limit was about 10(3) for milk. The highly specific nature of the technique was demonstrated by enumeration of E. coli 0157:H7 cells in the prese nce of large numbers of indigenous spoilage microorganisms in milk. Th is is the first known demonstration of the combination of DEFT and ant ibody probe technology for the specific enumeration of a microbe direc tly in food without a growth or enrichment step.