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.