Effects of Sublethal Treatments on the Variability of the Lag Phases in Salmonella Enterica Serovar Enteritidis and Listeria Innocu.

Abstract

This research work studied the variability of the lag phase in individual Salmonella enterica serovar Enteritidis and Listeria innocua cells after receiving inactivating acidification, irradiation and heat treatments. Once the protocol of experimental trials has been established; Bioscreen previously determined: the number of bacteria that generate a turbidity of 0,20 optical density, the detection time and the specific maximum growth rate; data indicating the lag phases in experimental conditions. However, to further refine the estimation of cells number per well and then calculate the lag phase of individual cells. Two strategies were proposed: 1) that all the growing samples contained a cell; 2) than a certain number of samples will contain one, two or more cells. So, if there are two, three or n viable cells, the lag phase of the population will be gradually shorter and, hopefully, less variable. The analyzed data concluded that the variability of the microorganisms under study increases when the growth substrate of the microorganism is more complex and when the growth temperature moves away from the optimum. From the lag phase point of view acidification is the most variable, instead irradiation is an excellent alternative to thermal treatment because, both for inactivation and for the lag phase of irradiated surviving microorganisms the results are more homogeneous and less variable.