Bacterial memory of persisters: Bacterial persister cells can retain their phenotype for days or weeks after withdrawal from colony-biofilm culture

Abstract

Persister cells, or persisters, are a specific subpopulation of bacterial cells that have acquired temporary antibiotic-resistant phenotypes. In this study, we showed that Escherichia coli produces many more persister cells in colony-biofilm culture than in the usual liquid culture and that these persisters can be maintained in higher numbers than those from liquid culture for up to 4 weeks at 37°C in a fresh, nutrient-rich, antibiotic-containing medium, even after complete withdrawal from the colony-biofilm culture. This suggests the presence of a long-retention effect, or "memory effect", in the persister cell state of E. coli cells. We also discovered that such increases in persisters during colony-biofilm culture and their memory effects are common, to a greater or lesser degree, in other bacterial species. This is true not only for gram-negative bacteria (Acinetobacter and Salmonella) but also for gram-positive bacteria (Staphylococcus and Bacillus). This is the first report to suggest the presence of a common memory mechanism for the persister cell state, which is inscribed during colony-biofilm culture, in a wide variety of bacteria.