Multiple antibiotic resistance in gram-negative bacteria: controlling cell envelope barrier function

Trigg, Alexandra Elizabeth (2023). Multiple antibiotic resistance in gram-negative bacteria: controlling cell envelope barrier function. University of Birmingham. Ph.D.

Preview

Trigg2023PhD.pdf
Text - Accepted Version
Available under License All rights reserved.
Download (15MB) | Preview

Abstract

Antimicrobial resistance is increasingly noted in clinical samples. The multiple antibiotic resistance (\(\textit{mar}\)) operon, found in many Gram-negative bacteria, contributes to an increase in susceptibility to a broad range of antibiotics. The \(\textit{mar}\) encoded activator, MarA, transcriptionally regulates a range of genes that contribute to multidrug resistance. Multidrug resistance can be caused by loss-of-function mutations in \(\textit{marR}\), encoding the repressor of the \(\textit{mar}\) operon. Investigating the mechanisms of MarA-related multiple drug resistance in Gram- negative bacteria is essential to understand widespread antibiotic resistance.

The outer membrane and peptidoglycan layer of Gram-negative bacteria acts as an external barrier to reduce diffusion of antimicrobial agents into the cytoplasm. This work has characterised the regulation of several novel MarA targets involved in outer membrane biosynthesis and peptidoglycan hydrolysis. MarA activates \(\textit{lpxC}\), \(\textit{lpxL}\) and \(\textit{waaY}\), which encode enzymes involved in LPS biosynthesis. Additionally, MarA represses \(\textit{pbpG}\), encoding a peptidoglycan hydrolase enzyme.

We hypothesised that MarA-regulated cell envelope genes could act synergistically to improve barrier function. Consistent with this, we found that combining defects in the cell wall and outer membrane barriers significantly changes antibiotic susceptibility. \(\textit{mlaFEDCB}\), encoding an ABC transport system involved in lipid trafficking, has previously been demonstrated to be activated by MarA. Mutating marboxes upstream of \(\textit{mlaFEDCB}\), \(\textit{waaY}\) and \(\textit{pbpG}\) independently caused no change in antibiotic susceptibility. However, mutating marboxes simultaneously resulted in significantly increased antibiotic susceptibility. Thus, this work predicts that MarA targets multiple cell envelope genes to improve barrier function, reducing antibiotic uptake and resulting in the \(\textit{mar}\) phenotype.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):