Title: Environmental factors influencing the relationship between optical density and cell count for Listeria monocytogenes
Authors: Francois, K ×
Devlieghere, F
Standaert, AR
Geeraerd, Annemie
Cools, I
Van Impe, Jan
Debevere, J #
Issue Date: 2005
Publisher: Blackwell Science
Series Title: Journal of Applied Microbiology vol:99 issue:6 pages:1503-1515
Conference: date:State Univ Ghent, Lab Food Microbiol & Food Preservat, Dept Food Safety & Food Qual, B-9000 Ghent, Belgium; Katholieke Univ Leuven, Dept Chem Engn, BioTeC Bioproc Technol & Control, Louvain, Belgium
Abstract: Aims: The effect of temperature (2-30 degrees C), pH (4(.)8-7(.)4) and water activity (0(.)946-0(.)995) on the relationship between optical density (OD) at 600 nm and the plate count (CFU ml(-1)) was investigated for Listeria monocytogenes. Methods and Results: Calibration curves, relating OD with plate counts, were collected by measuring the OD of consecutive one-half dilution series, before determining the cell density by classic plate count methods. The calibration curves were observed to be shifting in a parallel way, with increasing stress levels. Especially pH influenced the curve in a great extent, while the other variables were showing more synergetic effects. The reason for the shift was investigated by a microscopic viability test, showing a viability decrease with increasing stress levels, causing the shift of the calibration curve. In a last step a model was made describing the effect of environmental factors on the calibration curve, with different data transformations being tested. A polynomial equation was fitted to the data, taking into account a set of constraints to incorporate microbiological knowledge in the black box model. Hence, illogical interpolation results and overfitting of the data could be avoided. Conclusions: Different stress factors are affecting the relationship between the OD and the cell count of L. monocytogenes by lowering the cell viability. These effects could be modelled using a constrained polynomial model. Significance and Impact of the Study: The observed phenomena are important when calculating growth parameters, like growth rate and lag phase, based on OD data.
ISSN: 1364-5072
Publication status: published
KU Leuven publication type: IT
Appears in Collections:Bio- & Chemical Systems Technology, Reactor Engineering and Safety Section
Division of Mechatronics, Biostatistics and Sensors (MeBioS)
× corresponding author
# (joint) last author

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