The use of direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) to assess microbial populations on food contact surfaces

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Abstract
Two rapid methods, direct epifluorescent microscopy (DEM) and the direct epifluorescent filter technique (DEFT) on swab resuspension fluids, were compared with the traditional total viable count (TVC) on swab resuspension fluids for their ability to enumerate surface populations of attached bacteria. The degree of error in estimating surface populations was shown to be significantly less with DEM than DEFT followed by TVC. DEM estimated populations in the range 3 .times. 103 to 5 .times. 107 colonies/cm2 while DEFT enumerated populations above 3 .times. 104 colonies/cm2 and TVC above 3 .times. 105 colonies/cm2 (as measured by DEM). Swabbing was shown to remove a constant proportion of organisms from the surface populations tested, although below 3 .times. 105 colonies/cm2 most of the organisms remained in the cotton matrix and wee difficult to resuspend. DEFT was more able to enumerate swab resuspension fluids obtained from surface populations below 3 .times. 105 colonies/cm2 than was TVC.