Heterogeneity and the modelling of bacterial spore death: the case of continuously decreasing death rate

Abstract

Models for the inactivation of bacterial spores for the case of continuously decreasing death rate are reviewed and extended to show that it is not possible to distinguish between one particular model based upon the innate heterogeneity of the population and that based upon the acquisition of heat resistance during the heating process. Two innate heterogeneity models have been fitted to published data.

Growth and Heat Resistance Kinetic Variation Among Various Isolates of Salmonella and its Application to Risk Assessment

“…The survival curves considered can be characterized by an initial shoulder for small times, that, for large times, asymptotically approaches a straight line with slope equal to the negative of the inverse of the asymptotic D‐value. Many equations for describing nonlinear survival curves have been developed, ( 9 , 17‐22 ) some motivated by mechanistic considerations, others by just providing good empirical fits. In attempting to find a set of curves that provides a good fit to the observed data, three different functions were examined.…”

“…A second model considered, This is a modification of an equation developed by Han ( 17 ) for heat activation of spores, and further described by Sharpe and Bektash. ( 18 ) In those papers, the survival curves considered were convex, and there was a relationship of the parameter values such that second derivative of log 10 ( E ( r ( t ))) was positive for all t . For our application, if it is assumed that if a and b ≥ 0, then, for all t , the second derivative of log 10 ( E ( r ( t ))) is negative and as t →∞, the derivative →− k .…”

Resistência térmica de conidiósporos de <i>Aspergillus parasiticus</i> Speare ao calor seco, desenvolvimento de equipamento e ensaios.

“…Para a determinação da resistência termica pelo cãlcu1o de D, que e o numero de unidades de tempo para reduzir 90% dos esporos viãveis de uma população tratada a uma temperatura fixa qualquer, foi empregada a fÕrmula: SENO, 1956;MOLIN e OSTLUND, 1976); ativação e inativação simultâneas (HAN, 1977); diferenças na relação constante de ativação/constante de inativação a diferentes temperaturas (HERRMANN � a1ii, 1978); não homogeneidade das populações tratadas (SHULL � alii, 1963;EDWARD� alii, 1965;ALDER TON e SNELL, 1970;OTDA, 1970;BERG e SANDINE, 1970;BOND et alii, 1971;ADAMS e BUSTA, 1972;STUMBO, 1973;PULEO et li alii, 1975;MOLIN e USTLUND, 1975;SHARPE e BEKTASH, 1977;PEELER et alii, 1977;PULEO � alii, 1978); diferentes meca nismos de ativação a baixas e altas temperaturas (BERG e SANDINE, 1970;ADAMS e BUSTA, 1972); eficiência diferente na ativação por choque têrmico umido e seco (FOX e EDER, 1969); condicionamento prêvio intencional ou acidental (PRADO FILHO, 1975b;REYS et alii, 1981;PRADO FILHO, 1982).…”