Automatic enumeration of adherent streptococci or actinomyces on dental alloy by fluorescence image analysis

The aim of the present study was to develop an automated image analysis met hod to quantify adherence of Streptococcus sanguinis or Actinomyces viscosu s on surfaces of a currently used dental alloy. Counting such bacterial str ains was difficult because of their arrangement, thus S. sanguinis being a coccus arranged in chains or pairs, and A. viscosus a long complexly arrang ed polymorph rod. Direct counting of fluorescently stained adherent bacteri a was done visually and with image analysis methods. To differentiate these two morphotypes, two programs were developed: (i) for streptococci, thresh olding and selection of the object maxima, and (ii) for actinomyces, two st ep thresholding and processing of the characteristic points of the object s keletons. The triplicate enumerations for each bacterial strain were not si gnificantly different (p > 0.005) and correlations between visual counting and automated counting were significant (r = 0.91 for S. sanguinis and r = 0.99 for A. viscosus, p < 0.0001). These rapid and reproducible methods, al lowed us to count either cocci or rods, adherent on an inert substratum, in high density conditions. (C) 1999 Elsevier Science B.V. All rights reserve d.