COMPARISON OF LAG TIMES OBTAINED FROM OPTICAL DENSITY AND VIABLE COUNT DATA FOR A STRAIN OF PSEUDOMONAS FRAGI

ABSTRACT Values were obtained for the lag times of a strain of the meat spoilage bacterium Pseudomonas fragi under a variety of cultural conditions by analyzing optical density (OD) and viable count (VC) data using the Gompertz equation. Lag times produced from OD data were shorter than those derived from VC data. Observations showed that during the lag phase, cell length increased before the cells began to divide, explaining the apparent earlier resolution of lag phase observed with the OD measurement technique. By linear regression the general equation: Log (VC Lag time) = A + B.Log (OD Lag time) where A = 0.344 and B = 0.868 was derived to interconvert OD lag times and VC lag times. This equation was applied to predicted lag times derived from models that had been constructed using optical density data and that are used to predict growth kinetics of cold‐tolerant pathogens on foods. With this adjustment, the models demonstrated an improved predictive ability when compared to measured values for growth of these pathogens on foods.