Collateral Changes in Cell Physiology Associated with ADC-7 β-Lactamase Expression in Acinetobacter baumannii

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Acinetobacter baumannii is a high-priority pathogen with extensive antibiotic resistance.
• AmpC beta-lactamase (ADC) is chromosomally encoded in A. baumannii, implying a potential cellular role.
• Beta-lactam resistance contributes significantly to treatment failures in A. baumannii infections.

Purpose of the Study:

• To investigate the cellular function and vulnerabilities associated with ADC beta-lactamase overexpression in A. baumannii.
• To identify novel therapeutic targets for combating beta-lactamase-producing A. baumannii.
• To explore the impact of ADC-7 overexpression on bacterial physiology and antibiotic susceptibility.

Main Methods:

• Peptidoglycan composition analysis to assess changes in l,d-transpeptidase activity.
• Transposon insertion screening to identify genes essential for viability under ADC-7 overexpression.
• Gene deletion and overexpression studies of carbonic anhydrase (canB) and various beta-lactamases (ADC-7, OXA-23, TEM-1).
• Sensitivity testing against peptidoglycan synthesis inhibitors and ethoxzolamide.

Main Results:

• Overexpression of ADC-7 beta-lactamase altered peptidoglycan composition, suggesting modified l,d-transpeptidase activity.
• A transposon insertion in canB (carbonic anhydrase) led to loss of viability upon ADC-7 overexpression.
• canB deletion mutants showed amplified sensitivity to ADC-7 overexpression, and also to OXA-23 and TEM-1 overexpression.
• Reduced carbonic anhydrase activity increased sensitivity to ethoxzolamide and peptidoglycan synthesis inhibitors, with synergistic effects observed with fosfomycin.

Conclusions:

• ADC-7 beta-lactamase overexpression induces significant physiological changes in A. baumannii.
• The essential carbonic anhydrase CanB represents a novel target for antimicrobial agents.
• Carbonic anhydrase inhibitors may offer a new strategy to treat infections caused by beta-lactamase-overexpressing A. baumannii.