Heat adaptation of Escherichia coli K12: Effect of acid and glucose

AbstractThe objective of this work is to investigate the effect of the (possible) acid adaptation during growth in a glucose rich environment on the heat resistance of Escherichia coli K12 MG1655. E. coli cells were grown in TSB and/or TSB dextrose free broth until they reached the stationary phase. Afterwards, the stationary phase cells were added in TSB and/or TSB dextrose free broth and inactivation took place at 54oC and 58oC. It was observed that growth in a glucose rich environment leads to an increased heat resistance, most likely due to a certain level of acid and further heat adaptation via cross protection

Quantifying the combined effect of salt and temperature on the growth of <i>Listeria</i> strains isolated from salmon and salmon processing environments

The effects of temperature and salt concentration on the growth of relevant strains of L. monocytogenes and Listeria innocua, were quantified based on growth in a liquid broth medium, monitored by measuring turbidity. Absorbance curves were used to estimate maximum growth rate and lag time. The growth rates increase with increasing temperatures. The levels were quite similar for both species, although L. monocytogenes showed higher growth rate than L. innocua at 4 °C. Lag time was more affected both by temperature and salt concentration, and these effects were most prominent for L. innocua.</i

Optimal experiment design for dynamic bioprocesses: a multi-objective approach

status: publishe

On the trade-off between experimental effort and information content in optimal experimental design for calibrating a predictive microbiology model

In predictive microbiology, dynamic mathematical models are developed to describe microbial evolution under time-varying environmental conditions. Next to an acceptable model structure, reliable parameter values are necessary to obtain valid model predictions. To obtain these accurate estimates of the model parameters, labor-and cost-intensive experiments have to be performed. Optimal experimental design techniques for parameter estimation are beneficial to limit the experimental burden. An important issue in optimal experimental design, included in this work, is the sampling scheme. Recent work illustrates that identifying sampling decisions results in bang-bang control of the weighting function in the Fisher information matrix. A second point addressed in this work is the trade-off between the amount of time an experimenter has available for measurements on the one hand, and information content on the other hand. Recently, multi-objective optimization is applied to several different optimal experimental design criteria, whereas in this paper the workload expressed as when to sample, is considered. The procedure is illustrated through simulations with a case study for the Cardinal Temperature Model with Inflection. The viability of the obtained experiments is assessed by calculating the confidence regions with two different methods: the Fisher information matrix approach and the Monte-Carlo method approachstatus: publishe

Optimal experimenal design for microbial inactivation

31 pagesN

Role of growth morphology in the formulation of NaCl-based selective media for injury detection of Escherichia coli, Salmonella Typhimurium and Listeria innocua

Sublethal injury (SI) poses major public health concerns since injured cells are responsible for serious limitations in food diagnostics and are susceptible to recovery, often developing adaptive stress responses. Detection of SI is based on the difference in plate counts between non-selective media, which represent the total cell population, and selective media, to which injured cells become sensitive. Selective media for detection of sublethal membrane damage are often based on NaCl supplement, although there is a lack of consensus in the literature about appropriate levels. Planktonic cells are generally used to investigate SI mechanisms, although they often exhibit different stress tolerance than cell colonies in/on solid food (model) systems. In this work, the effect of growth morphology, colony size and concentration of the gelling agent in the growth media, on the maximum non-inhibitory NaCl concentration in the plating medium was assessed for Escherichia coli, Salmonella Typhimurium and Listeria innocua. Stationary phase cultures of planktonic cells and large and small colonies grown in either 1.5% (w/v) xanthan gum-based system or 2.5% (w/v) xanthan gum-based system exhibited significantly different viable counts and osmotolerance. The effect of cell arrangement and xanthan gum percentage in the growth media depended on the microorganism under investigation. Additionally, differences in the maximum non-inhibitory concentration were evident, with 5.0% (w/v) NaCl for the Gram-negative bacteria and 6.5% (w/v), for L. innocua. Different extent of colony shrinkage and morphological damage was observed as NaCl concentration in the plating medium increased. This information will contribute to define NaCl-based selective media for accurate SI detection under realistic scenarios. © 2014