Investigating the dynamics of expression of persister genes in Escherichia coli responding to environmental changes

Abstract

Antibiotics have been a one of the many wonders of modern medicine, improving life quality and saving lives on daily basis. Their misuse has caused decreased efficacy worldwide, which is becoming a serious public health threat. An important aspect of decreased antimicrobial efficacy is antibiotic tolerance, of which persisters and Viable but not Culturable (VBNC) cells are important examples: they survive the antibiotic treatment and can give rise to a new population. Therefore, their presence in otherwise susceptible cultures has been implied in recurring infections, threatening safety of food and of water supplies. So far, no obvious markers for these cells have been identified. These tolerant cells appear randomly in bacterial populations, but their existence is also a form of adaptation to environmental challenges, like the presence of antimicrobial drugs. Independently from their susceptibility, all bacterial cells must constantly fine tune their responses to such challenges, and to interact with their surroundings. Signals from the external environment are transmitted across signalling pathways and influence bacterial gene expression. RNA in its different forms, like mRNA, is the link of this communication between the external world and the cell’s DNA. For this project, RNA was extracted during the lag phase of Escherichia coli BW25113 (wild type) growth in LB medium. Examples of transcriptomics results presented here show that E. coli respond to changes in the culture conditions, like medium temperature and pH. This work also presents a protocol for RNA extractions from E. coli persisters and VBNC cells in exponential phase, after 3 hours of challenge with ampicillin. They did not yield consistent results in terms of RNA quantity but could become a steppingstone to further investigation of the tolerant phenotypes in E. coli.