Three concurrent mechanisms generate gene copy number variation and transient antibiotic heteroresistance

Area of Science:

• Microbiology
• Genetics
• Pharmacology

Background:

• Heteroresistance, where resistant bacteria hide in susceptible populations, compromises antibiotic efficacy.
• The genetic and physiological basis of heteroresistance is not well understood.

Purpose of the Study:

• To investigate the mechanisms driving heteroresistance in Klebsiella pneumoniae.
• To determine the prevalence and impact of these mechanisms in clinical isolates.

Main Methods:

• Analysis of a multi-resistant Klebsiella pneumoniae isolate.
• Gene dosage studies to identify resistance drivers.
• Mouse gut colonization model for in vivo efficacy testing.
• Prevalence study on Escherichia coli bloodstream isolates.

Main Results:

• Identified tandem amplification, increased plasmid copy number, and gene transposition as key drivers of heteroresistance.
• These mechanisms confer fitness costs and are genetically unstable, reverting to susceptibility without antibiotic pressure.
• Elevated resistance-gene dosage led to antibiotic treatment failure in a mouse model.
• Identified mechanisms are prevalent in clinical Escherichia coli isolates.

Conclusions:

• Gene dosage is a critical factor in heteroresistance.
• Understanding plasmid-mediated mechanisms is crucial for combating antibiotic resistance.
• Clinical isolates demonstrate the widespread relevance of these findings.