Type Ib partitioning systems of staphylococcal and enterococcal resistance plasmids

Abstract

Since the introduction of antibiotics into clinical use for the treatment of bacterial infections, resistance has repeatedly emerged and current levels of resistance represent a significant threat to patient outcomes in both healthcare and community settings. Collectively, the main drivers of antibiotic resistance emergence and spread are mobile genetic elements, such as insertion sequences, transposons, and plasmids, the latter of which can confer resistance to multiple antimicrobial agents. These multiresistance plasmids exist at low copy-numbers and generally contain a toolkit of maintenance mechanism, such as Type Ib plasmid partitioning systems, which ensure plasmid copies are stably maintained during cell division, even in the absence of selection pressure for the phenotypes that they confer. Data presented in this thesis provides an important mechanistic overview of how Type Ib partitioning systems function in coccoid organisms and confirms their similarity with well-studied systems. Specifically, functional studies, combined with site-directed mutagenesis, have confirmed the requirement of both ParA and ParB for plasmid stability. Additionally, DNA-binding studies and reporter assays have also confirmed that ParB binds to predicted parS sites and regulates transcription of the par operon. Interestingly, in the case of the pJEG029 system, the ParB protein also regulates the repA gene, and this is the first report of such regulation where the replication gene is located in a separate operon. Furthermore, cytological studies using the staphylococcal system have for the first time revealed that ParA displays dynamic movement within coccoid cells in association with the bacterial nucleoid, which is consistent with the current model for Type I partitioning systems; note that ParB also appears to enhance this movement. Collectively, the results presented in this thesis address a serious knowledge gap and provide a detailed mechanistic understanding of staphylococcal and enterococcal Type Ib plasmid partitioning systems. Ultimately, this and future studies will help provide opportunities for the development of targeted interventions aimed at disrupting resistance plasmid carriage and transfer, and thus the spread of antibiotic resistance.

Date of Award	2020
Original language	English