RECOMMENDATIONS FOR CALCULATING GROWTH-PARAMETERS BY OPTICAL-DENSITY MEASUREMENTS

An automated turbidimetric system, Bioscreen C, was used to monitor ba cterial growth in microplates. The detection threshold and linear rang e of the instrument were determined. Bioscreen C was found to present certain problems in setting up temperature and O.D. stability. A syste matic way to calculate growth parameters (maximal growth rate, lag tim e and logarithmic increase of population) was developed. The repeatabi lity of growth was studied. The validity of the method was illustrated by studying the growth of 9 strains of Listeria monocytogenes under t wo conditions: 37 degrees C, Aw 0.96, pH 7.0 and 10 degrees C, Aw 1.00 , pH 7.0. Growths in Bioscreen C were compared with growth obtained in a fermenter.