Characterization of Amino Acid Substitutions in the Two-Component Regulatory System AdeRS Identified in...

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Acinetobacter baumannii utilizes resistance-nodulation-cell division (RND)-type efflux pumps, like AdeABC, as a key mechanism for antimicrobial resistance.
• Mutations in the two-component regulatory system AdeRS are frequently observed in multidrug-resistant (MDR) strains, correlating with increased efflux pump expression.

Purpose of the Study:

• To investigate the functional impact of specific, commonly identified amino acid substitutions (D21V and D26N in AdeR; T156M in AdeS) on the AdeABC efflux system.
• To determine the effect of these mutations on *adeB* gene expression, efflux activity, and antimicrobial susceptibility in *A. baumannii*.

Main Methods:

• Reverse transcription-quantitative PCR (qRT-PCR) to quantify *adeB* mRNA levels.
• Accumulation assays to measure intracellular drug accumulation, indicating efflux activity.
• Antimicrobial susceptibility testing using agar dilution and broth microdilution to determine Minimum Inhibitory Concentrations (MICs).

Main Results:

• The D26N substitution in AdeR and the T156M substitution in AdeS significantly increased *adeB* expression and efflux activity.
• These mutations correlated with increased MICs for various antimicrobial classes, confirming their role in the MDR phenotype.
• The D21V substitution in AdeR did not affect *adeB* expression or antimicrobial susceptibility.

Conclusions:

• The D26N (AdeR) and T156M (AdeS) substitutions are critical drivers of the MDR phenotype in *A. baumannii* by upregulating the AdeABC efflux pump.
• These specific regulators represent potential therapeutic targets for developing strategies to overcome antimicrobial resistance.
• Understanding these regulatory mutations aids in predicting resistance and developing novel approaches to combat MDR infections.