Citation:
Lambert, Ronald J. W., A new model for the effect of pH on microbial growth: an extension of the Gamma
hypothesis, Journal of Applied Microbiology, Volume 110, Issue 1, January 2011,
Pages 61–68.
Abstract:
Aims: To investigate the appropriateness of the extended Lambert-Pearson model
(ELPM) to model the effect of pH (as hydrogen and hydroxyl ions) over the whole
biokinetic pH range in comparison with other available models. Methods and
Results: Data for the effect of pH on microbial growth were obtained from the
literature or in-house. Data were examined using several models for pH. Models
were compared using the residual mean of squares. Using the ELPM, pH was
modelled as hydrogen ions and hydroxyl ions; hence, the model was monotonic in
each. The ELPM was able to model data more successfully than the cardinal pH
model (CPM) and other models in the majority of cases. Conclusions: Examining
the effect of pH as hydrogen and hydroxyl ions has the advantage that the basic
form of the ELPM can be retained as each is treated as a distinct antimicrobial
effect. With the ELPM, each inhibitor is described by two parameters; from these
parameters, the pH(min), pH(opt) and pH(max) can be obtained. Furthermore, the
idea of a dose response, absent from other models, becomes important.
Significance and Impact of the Study: The CPM is an excellent model for certain
situations - where there is a high degree of symmetry between the suboptimal pH
and superoptimal pH response and where there are few data points available. The
ELPM is more amenable to highly asymmetric behaviour, especially where plateaus
of effect around the pH optimum are observed and where the number of data points
is not restrictive.