(107c) Viable but Non-Culturable and Persistence Describe the Same Bacterial Stress State (invited talk)

Bacteria are often thought of as having two dormant phenotypes: the viable but non-culturable (VBNC) state and the persister state. Persister cells are a multi-drug tolerant subpopulation of bacteria that contribute to chronic and recalcitrant clinical infections such as cystic fibrosis and tuberculosis, and we have demonstrated that persister cells are metabolically dormant (Antimicrob. Agents Chemother. 57:1468–1473, 2013). VBNC cells are formed during stresses like extended starvation and are reported to not be resuscitated under normal conditions. We investigated the relatedness of the two stress-induced phenotypes at the single-cell level to examine cell morphology and quantify cell resuscitation (Environ. Microbiol. on-line 2018, doi: 10.1111/1462-2920.14075). Using the classic starvation conditions to create VBNC cells, we found that the majority of the remaining Escherichia coli K-12 population are spherical, have empty cytosol, and fail to resuscitate; however, some of the spherical cells resuscitate immediately. Critically, all the culturable cells in this starved population became persister cells within 14 days of starvation (similar results were found with the environmental isolate E. coli O157:H7 EDL933). We found that the persister cells initially are rod-like, have clear but limited membrane damage, can resuscitate immediately, and gradually become spherical by aging. After 24 h, only rod-shaped persister cells survive, and all the spherical cells lyse. Both cell populations formed under the VBNC-inducing conditions and the persister conditions are metabolically inactive. Therefore, the bacterial population consists of dead cells and persister cells in the VBNC-inducing conditions; i.e., the non-lysed particles that do not resuscitate are dead, and the dormant cells that resuscitate are persister cells. Hence, “VBNC” and “persister” describe the same dormant phenotype. In this presentation, we will also demonstrate that persister cells wake immediately when presented with nutrients and that they wake as a function of their ribosome content (Environ. Microbiol. on-line 2018, doi: 10.1111/1462-2920.14093).