Second-order functions are the simplest correlations between flow cytometric light scatter and bacterial diameter

Second-order mathematical relationships between bacterial cell diameter det ermined by electric particle analyser and flow cytometric forward light sca tter in axenic cultures are obtained and discussed. Since it is technically impossible today to obtain both measurements for each individual cell, sta ndard regression techniques cannot be applied. To overcome this limitation, we assume that these two parameters are related by a monotone increasing f unction that enables their mathematical relationships to be studied. Our co nclusion is that forward light scatter data cannot be linearly transformed into bacterial size values by an accurate and universal function. However, second-order relationships seem to be the simplest satisfactory relationshi ps between cell diameter and forward light scatter in eubacteria. (C) 2000 Elsevier Science B.V. All rights reserved.