Functional Genetics Of Capsule Phase Variation In Antibiotic Resistant Bacterial Pathogens

Capsular polysaccharides are major virulence factors and therapeutic targets in antibiotic-resistant (AMR) bacterial pathogens such as Klebsiella pneumoniae (Kp). While capsules are known to inhibit phagocytosis and complement-mediated lysis, they also impede epithelial colonisation and uptake of foreign DNA, raising the question: ‘how do encapsulated pathogens colonise the host, acquire AMR, and cause severe infections?’. I have identified an ON/OFF genetic switch of Kp capsule expression, driving a reversible ‘phase variation’ between systemic immune evasion, and colonisation/AMR acquisition. I show this mechanism is conserved in Kp and present in multiple additional AMR pathogens. Thus, I have established a prototype system to study the role of capsule phase variation in AMR pathogen biology. Here, we will characterise genetic determinants of capsule phase variation rate in Kp using comparative genomics of ~1000 clinical isolates, and in vitro assays with representative strains. We will define the role of capsule phase variation in immune evasion, bacterial population fitness in vivo, and the evolution of antibiotic resistance. In later years, we will extend this vision to the two additional AMR pathogens Escherichia coli and Acinetobacter baumannii, identifying conserved mechanisms of virulence regulation which will facilitate development of novel therapeutics and slow the spread of AMR.