  A hallmark of bacterial populations cultured in vitro is their homogeneity of
growth, where the majority of cells display identical growth rate, cell size
and content. Recent insights, however, have revealed that even cells growing in
exponential growth phase can be heterogeneous with respect to variables
typically used to measure cell growth. Bacterial heterogeneity has important
implications for how bacteria respond to environmental stresses, such as
antibiotics. The phenomenon of antimicrobial persistence, for example, has been
linked to a small subpopulation of cells that have entered into a state of
dormancy where antibiotics are no longer effective. While methods have been
developed for identifying individual non-growing cells in bacterial cultures,
there has been less attention paid to how these cells may influence growth in
colonies on a solid surface. In response, we have developed a low-cost,
open-source platform to perform automated image capture and image analysis of
bacterial colony growth on multiple nutrient agar plates simultaneously. The
descriptions of the hardware and software are included, along with details
about the temperature-controlled growth chamber, high-resolution scanner, and
graphical interface to extract and plot the colony lag time and growth
kinetics. Experiments were conducted using a wild type strain of Escherichia
coli K12 to demonstrate the feasibility and operation of our setup. By
automated tracking of bacterial growth kinetics in colonies, the system holds
the potential to reveal new insights into understanding the impact of microbial
heterogeneity on antibiotic resistance and persistence.
