Chapter 10 - Bacterial Growth, Culturability and Viability

Abstract

For most of the 20th century ideas of the growth and life cycles of bacteria were dominated by the concepts of lag, exponential, stationary and death phases and analogies with the eukaryotic cell cycle were largely rejected. While the classical growth phases remain key points of reference, the last 20 years have seen an explosion of molecular and cytological results showing the diversity of bacterial physiological adaptive states and indicating cyclical events beyond a headlong accumulation of biomass; there is clearly more to bacteria than growing, not growing or dying. Since growth is integral to infection we would like to know the growth state of bacteria in a medically relevant sample. In this chapter, bacterial growth is reviewed from a molecular perspective considering the signals that might indicate the status of cells in a sample. Major advances have been made in describing cell replication and division and, in particular, the development of microfluidic systems linked to imaging has made it possible to follow the fate of cells through many generations. We are beginning to appreciate the consequences of asymmetric cell division and how this further underpins the diversity of cells in a bacterial population where once all those comprising a balanced exponential phase culture were considered identical with respect to their time since division. The concepts of viability and culturability remain a challenge and it is necessary now to link them up with the avalanche of data emerging from microbiomic studies applied to human samples.