Kinetics of E.coli colony area expansion and color development in Chromocult® Coliform Agar (CCA) under different incubation conditions

Abstract

Effects of thermal stress on E. coli colony growth kinetic using Chromocult® Coliform Agar (CCA) was investigated to indicate the optimal incubation temperature and accelerate colony expansion as well as color accentuation. E.coli colonies were cultured on CCA plate and different temperatures ranging from 30 to 45oC were applied to observe E.coli colony growth under thermal stress. The colony imagery was digitized using a digital microscopy equipped with size measurement capability. The colony area in pixels was evaluated and the color development using RGB indices was monitored over 48 h of incubation. Logistic model was utilized to estimate key kinetic parameters (i.e., the maximum specific growth rate and the asymptotic colony area). The colony expansion profiles indicated the optimal range of E. coli colony growth was between 37 and 40oC. High incubation temperature (i.e., 45oC) together with the inhibitory effect from the selective agent in CCA ceased E. coli growth. The colony color development was correlated well with the colony size and incubation temperature. After 16 h of incubation, the colony color saturated while colony size kept expanding for 48 h. Proper incubation temperature was critical to develop unique chromatic quality and played a vital role to escalate color identity of E. coli colony in CCA.