A MexR Mutation Which Confers Aztreonam Resistance to Pseudomonas aeruginosa

Area of Science:

• Microbiology
• Genetics
• Pharmacology

Background:

• Pseudomonas aeruginosa infections are difficult to treat due to high antibiotic resistance.
• Genomic mutations in P. aeruginosa contribute to antibiotic resistance and host adaptation.
• Understanding resistance mechanisms is crucial for designing effective combination therapies.

Purpose of the Study:

• To elucidate the aztreonam resistance mechanism in a clinical P. aeruginosa isolate (ARP36) compared to a sensitive isolate (CSP18).
• To identify the specific genetic and transcriptional changes responsible for aztreonam resistance.

Main Methods:

• Comparative analysis of a resistant (ARP36) and sensitive (CSP18) P. aeruginosa clinical isolate.
• RNA sequencing (RNAseq) to compare global transcriptional profiles.
• Genomic DNA resequencing to compare genomic profiles.
• Gene editing to simulate mexR mutation in the sensitive isolate.

Main Results:

• A R70Q substitution in the MexR protein was identified in the resistant isolate ARP36.
• This substitution led to the hyperexpression of the MexAB-OprM efflux pump, conferring aztreonam resistance.
• Gene editing confirmed that the R70Q substitution in MexR is sufficient to confer aztreonam resistance.
• The R70Q substitution impairs MexR binding to the mexAB-oprM operon's regulatory region without affecting dimerization.

Conclusions:

• The R70Q substitution in MexR is a key mechanism driving aztreonam resistance in this clinical P. aeruginosa isolate.
• This study provides the first explanation for how the R70Q substitution leads to derepression of mexAB-oprM.
• Findings contribute to understanding antibiotic resistance in P. aeruginosa and may inform future therapeutic strategies.