A model of microbial survival after exposure to pulsed electric fields

Survival curves of microorganisms exposed to pulsed electric fields have a characteristic sigmoid shape when plotted in linear coordinates. They can be described by the phenomenological model S(V, n) - 100/(1 + exp(V - Vc(n)) /a((n))) where S(V, n) is the percent surviving organisms, V the field intensity, n the number of pulses, Vc(n) critical field intensity corresponding to 50% survival and a(n) a constant representing the curve's steepness (about 90% of the loss in number occurs within Vc ± 3a). Testing the model with published data showed an excellent fit. Moreover, both Vc(n) and a(n) could be described in terms of a single exponential decay term, indicative of the increased lethality of the field as the number of pulses increases. These enabled the creation of three dimensional plots of the survival-field intensity-number of pulses relationships, with linear or semi-logarithmic scales, from which similarity and differences in resistance can be revealed at a glance. The tabulated model's constants can also be used for quantitative comparison of the survival curves of different organisms. WhenV ≫ Vc the model is reduced to log[S(V, n)/100] = -V/a(n), that is it entails the same type of semi-logarithmic relationship between survival and field intensity, a relationship that is traditionally used to present survival curves.