Accurate flow cytometric measurement of bacteria concentrations

Accurate measurements of bacteria concentrations are required in numerous studies; they raise methodological problems that complicate, for instance, the investigations of polymorphonuclear neutrophil functions. We propose a new flow cytometric method of determining bacteria concentrations by comparison with a standardized fluorescent latex bead solution. Relative counts of beads and bacteria are established in a system using both fluorescence and light scatter for the two types of particles. On the one hand, the latex bead size (0.98 microns in diameter) permits counting on traditional hematological counters and, on the other, a flow cytometric detection with the same conditions for bacteria. The reproducibility of the study of bacteria concentration measurements gave a coefficient of variation of < 5%.