Cronobacter Support
05-22-2009, 07:52 PM
1st International Conference on Cronobacter Poster Abstract 50
Modelling of thermal inactivation of Cronobacter sakazakii type strain, ATCC 29544, at 60°C in reconstituted infant formula milk.
C. sakazakii, an emerging food pathogen associated with neonatal meningitis, has been found to be more resistant to high temperature treatments in dairy products, than many other Enterobacteriaceae. The objective of this research was to compare the applicability of the primary models for describing the thermal inactivation of C. sakazakii in IMF. C. sakazakii strain, 29544, was used to assess heat resistance, using rubber sealed thin walled glass tubes. Stationary cells were suspended in IMF, divided into 1ml aliquots and heated at 60°C for up to 180 minutes. Samples were removed from the water-bath at one min intervals, cooled on ice and duplicate samples were plated on Tryptone Soya Agar (Oxoid, Basingstoke England) using the spread plate technique. Duplicate experiments were carried out on three separate occasions. Nonlinear microbial survival models (Weibull, modified Weibull and mixed Weibull distributions), which cover a wide range of known inactivation curvatures for vegetative cells, were fitted to the inactivation data and evaluated. Fitted models were also validated by comparing the predicted model parameters with the experimental values. Based on statistical indices and model characteristics, each model parameter reflected a survival characteristic, and all the models were flexible. The Weibull, the modified Weibull and the Mixed Weibull model fitted well to the experimental values (R2>0.79; RMSE <1.06). The isothermal inactivation of C. sakazakii in media was better described by three nonlinear kinetic models, the Weibull-type, the modified Weibull and the mixed Weibull models. Analytical results showed that root mean square error values (RMSE) of the models to be 0.74, 0.33 and 0.77 respectively, at 60°C. The distinct tailing of strain 29544 at 60°C was attributed to the presence of a heat-resistant subpopulation. The Mixed Weibull model conveniently accounts for the frequently observed nonlinearity of semi-logarithmic survivor curves, and the classical first-order approach is a special case of the Weibull model. The characteristic 4 log reduction values were exponentially correlated to the temperature and were found to decrease from 8.4 min to 0.6 min for mixed weibull model. Results of this study indicate that the mixed weibull model adequately describes the non linear inactivation of C. sakazakii in media and the bacterial resistance towards temperature.
Jenna M. Warby, Francis Butler, B. Tiwari, Séamus Fanning, Ciara Walsh and Amalia Scannell
College of Life Sciences,School of Agriculture, Food Science & Veterinary Medicine, UCD Agriculture and Food Science Centre, UCD, Dublin, Belfield, Dublin 4, Ireland.
Modelling of thermal inactivation of Cronobacter sakazakii type strain, ATCC 29544, at 60°C in reconstituted infant formula milk.
C. sakazakii, an emerging food pathogen associated with neonatal meningitis, has been found to be more resistant to high temperature treatments in dairy products, than many other Enterobacteriaceae. The objective of this research was to compare the applicability of the primary models for describing the thermal inactivation of C. sakazakii in IMF. C. sakazakii strain, 29544, was used to assess heat resistance, using rubber sealed thin walled glass tubes. Stationary cells were suspended in IMF, divided into 1ml aliquots and heated at 60°C for up to 180 minutes. Samples were removed from the water-bath at one min intervals, cooled on ice and duplicate samples were plated on Tryptone Soya Agar (Oxoid, Basingstoke England) using the spread plate technique. Duplicate experiments were carried out on three separate occasions. Nonlinear microbial survival models (Weibull, modified Weibull and mixed Weibull distributions), which cover a wide range of known inactivation curvatures for vegetative cells, were fitted to the inactivation data and evaluated. Fitted models were also validated by comparing the predicted model parameters with the experimental values. Based on statistical indices and model characteristics, each model parameter reflected a survival characteristic, and all the models were flexible. The Weibull, the modified Weibull and the Mixed Weibull model fitted well to the experimental values (R2>0.79; RMSE <1.06). The isothermal inactivation of C. sakazakii in media was better described by three nonlinear kinetic models, the Weibull-type, the modified Weibull and the mixed Weibull models. Analytical results showed that root mean square error values (RMSE) of the models to be 0.74, 0.33 and 0.77 respectively, at 60°C. The distinct tailing of strain 29544 at 60°C was attributed to the presence of a heat-resistant subpopulation. The Mixed Weibull model conveniently accounts for the frequently observed nonlinearity of semi-logarithmic survivor curves, and the classical first-order approach is a special case of the Weibull model. The characteristic 4 log reduction values were exponentially correlated to the temperature and were found to decrease from 8.4 min to 0.6 min for mixed weibull model. Results of this study indicate that the mixed weibull model adequately describes the non linear inactivation of C. sakazakii in media and the bacterial resistance towards temperature.
Jenna M. Warby, Francis Butler, B. Tiwari, Séamus Fanning, Ciara Walsh and Amalia Scannell
College of Life Sciences,School of Agriculture, Food Science & Veterinary Medicine, UCD Agriculture and Food Science Centre, UCD, Dublin, Belfield, Dublin 4, Ireland.