On-site Method for Detecting Bacteria Using Flow Cytometer

Abstract

  We have investigated the usefulness of on-site detection technique using flow cytometer for the screening of bacteria. The machine, “MICROCYTE”, used in this experiment provides us with the information of size (positional indication 1-240, 0.4-15 μm) and number of particles in the sample solution. Four vegetative bacteria (Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Yersinia pseudotuberculosis) showed a similar flow cytometric distribution pattern of the peak center of about 40, and the particle numbers were 10¹¹-10¹² cells per wet volume (g). The spores of Bacillus subtilis and dry yeast showed somewhat larger particles (peak center: 103 and 193). The flow cytometric patterns of “white powder”, wheat flour, starch and detergent were quite different from those of bacteria. The patterns of pepper, soybean flour, sugar and chalk were similar to those of bacteria, but particle numbers per wet volume were quite few, compared to those of bacteria. From the sample of salt, only very few particles were observed. Therefore, it is possible to distinguish such white powders from bacteria in their flow cytometric distribution patterns. The flow cytometric pattern of the mixed solution of bacteria and white powders showed the presence of bacteria clearly. The autoclave treatment shifted the histogramic position to the smaller size, and decreased the particle number, but still made it possible to detect bacteria.