Collaborative trial of the direct epifluorescent filter technique (DEFT), a rapid method for counting bacteria in milk

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Abstract
The direct epifluorescent filter technique (DEFT) is a new rapid method which uses membrane filtration and epifluorescent microscopy for counting bacteria in milk. A collaborative trial of the DEFT was conducted between 6 laboratories. Each laboratory obtained a highly significant relationship between the DEFT count and plate count with a correlation coefficient generally > 0.9 but there were significant differences between these relationships. The repeatability of the DEFT, although .apprx. 1.5 times worse than that of the plate count, was of a level acceptable in practice. Reproducibility of the DEFT was .apprx. 3 times that of the plate count. This poor reproducibility was probably mainly due to counting errors. Possible reasons for this and ways of reducing counting errors are discussed.