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Applied and Environmental Microbiology, November 2000, p. 4979-4987, Vol. 66, No. 11
School of Agricultural Science, University of
Tasmania, Hobart, Tasmania 7001, Australia
Received 21 October 1999/Accepted 7 September 2000
Models describing the limits of growth of pathogens under multiple
constraints will aid management of the safety of foods which are
sporadically contaminated with pathogens and for which subsequent
growth of the pathogen would significantly increase the risk of
food-borne illness. We modeled the effects of temperature, water
activity, pH, and lactic acid levels on the growth of two strains of
Listeria monocytogenes in tryptone soya yeast extract broth. The results could be divided unambiguously into "growth is
possible" or "growth is not possible" classes. We observed minor
differences in growth characteristics of the two L. monocytogenes strains. The data follow a binomial probability
distribution and may be modeled using logistic regression. The model
used is derived from a growth rate model in a manner similar to that
described in a previously published work (K. A. Presser, T. Ross,
and D. A. Ratkowsky, Appl. Environ. Microbiol. 64:1773-1779,
1998). We used "nonlinear logistic regression" to estimate the
model parameters and developed a relatively simple model that describes
our experimental data well. The fitted equations also described well
the growth limits of all strains of L. monocytogenes
reported in the literature, except at temperatures beyond the limits of
the experimental data used to develop the model (3 to 35°C). The
models developed will improve the rigor of microbial food safety risk
assessment and provide quantitative data in a concise form for the
development of safer food products and processes.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Growth Limits of Listeria monocytogenes
as a Function of Temperature, pH, NaCl, and Lactic Acid

*
Corresponding author. Mailing address: School of
Agricultural Science, University of Tasmania, G.P.O. Box 252-54, Hobart, Tasmania 7001, Australia. Phone: 61-3-62261831. Fax:
61-3-62262642. E-mail: Tom.Ross{at}utas.edu.au.
Present address: Department of Medical Sciences, Ministry of Public
Health, Nontaburi, Thailand.
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