Recommendations for calculating growth parameters by optical density measurements

An automated turbidimetric system, Bioscreen C, was used to monitor bacterial growth in microplates. The detection threshold and linear range of the instrument were determined. Bioscreen C was found to present certain problems in setting up temperature and O.D. stability. A systematic way to calculate growth parameters (maximal growth rate, lag time and logarithmic increase of population) was developed. The repeatability of growth was studied. The validity of the method was illustrated by studying the growth of 9 strains of Listeria monocytogenes under two conditions: 37°C, Aw 0.96, pH 7.0 and 10°C, Aw 1.00, pH 7.0. Growths in Bioscreen C were compared with growth obtained in a fermentor.