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Applied and Environmental Microbiology, December 2002, p. 5816-5825, Vol. 68, No. 12
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.12.5816-5825.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.

Modeling the Lag Time of Listeria monocytogenes from Viable Count Enumeration and Optical Density Data

F. Baty,1* J. P. Flandrois,1 and M. L. Delignette-Muller2

CNRS UMR 5558, Laboratoire de Bactériologie, Faculté de Médecine Lyon-Sud, 69921 Oullins Cedex,1 Unité de microbiologie alimentaire et prévisionnelle, École Nationale Vétérinaire de Lyon, 69280 Marcy l'Etoile, France2

Received 9 May 2002/ Accepted 21 August 2002

The following two factors significantly influence estimates of the maximum specific growth rate (µmax) and the lag-phase duration ({lambda}): (i) the technique used to monitor bacterial growth and (ii) the model fitted to estimate parameters. In this study, nine strains of Listeria monocytogenes were monitored simultaneously by optical density (OD) analysis and by viable count enumeration (VCE) analysis. Four usual growth models were fitted to our data, and estimates of growth parameters were compared from one model to another and from one monitoring technique to another. Our results show that growth parameter estimates depended on the model used to fit data, whereas there were no systematic variations in the estimates of µmax and {lambda} when the estimates were based on OD data instead of VCE data. By studying the evolution of OD and VCE simultaneously, we found that while log OD/VCE remained constant for some of our experiments, a visible linear increase occurred during the lag phase for other experiments. We developed a global model that fits both OD and VCE data. This model enabled us to detect for some of our strains an increase in OD during the lag phase. If not taken into account, this phenomenon may lead to an underestimate of {lambda}.


* Corresponding author. Mailing address: CNRS UMR 5558, Laboratoire de Bactériologie, Faculté de Médecine Lyon-Sud, BP 12, 69921 Oullins Cedex, France. Phone: 33-4-7886-3167. Fax: 33-4-7886-3149. E-mail: baty{at}biomserv.univ-lyon1.fr.


Applied and Environmental Microbiology, December 2002, p. 5816-5825, Vol. 68, No. 12
0099-2240/02/$04.00+0     DOI: 10.1128/AEM.68.12.5816-5825.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.




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Copyright © 2002 by the American Society for Microbiology. All rights reserved.