Fluorescent Antibodies Applied to Direct Epifluorescent Filter Technique for Microscopic Enumeration of Escherichia coli 0157:H7 in Milk and Juice

Abstract

In a modification of the direct epifluorescent filter technique (DEFT), direct fluorescent antibody staining was used for the rapid (<1 h), specific enumeration of foodbome Escherichia coli 0157:H7 by epifluorescence microscopy. Cell counts obtained by this method (Ab-DEFT) correlated well with DEFT counts obtained by acridine orange staining and with viable plate counts ranging from 108 to 101 cells per ml for pure cultures in buffer. Ab-DEFT also was effective for counting E. coli 0157:H7 cells inoculated into milk and juice; the sensitivity limit was about 103 for milk. The highly specific nature of the technique was demonstrated by enumeration of E. coli 0157:H7 cells in the presence of large numbers of indigenous spoilage microorganisms in milk. This is the first known demonstration of the combination of DEFT and antibody probe technology for the specific enumeration of a microbe directly in food without a growth or enrichment step.