Involvement of hpap2 and dgkA Genes in Colistin Resistance Mediated by mcr Determinants

Area of Science:

• Microbiology
• Molecular Biology
• Antimicrobial Resistance

Background:

• Plasmid-mediated colistin resistance (mcr) genes compromise polymyxin effectiveness against Gram-negative pathogens.
• Key mcr genes, mcr-1 and mcr-3, are often linked to hpap2 and dgkA, respectively, whose functions remain unclear.
• Understanding the interplay between mcr genes and host cell metabolism is crucial for combating antibiotic resistance.

Purpose of the Study:

• To investigate the role of mcr-1 and mcr-3, individually and co-expressed with hpap2 or dgkA, in colistin resistance.
• To analyze the impact of mcr expression on genes involved in phospholipid metabolism and lipopolysaccharide modification.
• To elucidate the contribution of hpap2 and dgkA to colistin resistance mechanisms.

Main Methods:

• Expression of mcr-1, mcr-3, mcr-1-hpap2, and mcr-3-dgkA in Escherichia coli.
• Antimicrobial susceptibility testing of recombinant strains.
• Quantitative analysis of gene expression related to phospholipid metabolism and LPS modification.

Main Results:

• Single mcr-1 or mcr-3 genes conferred growth on colistin selective media; co-expression with hpap2 or dgkA resulted in maximal resistance.
• mcr expression downregulated genes involved in LPS modification and phospholipid recycling, including arnB, ybjG, pmrR, eptA, lpxT, dgkA, bacA, and pgpB.
• Cells expressing mcr determinants showed resistance to bacitracin, indicating altered undecaprenyl pyrophosphate (UPP) metabolism.

Conclusions:

• mcr-1 and mcr-3 alone are sufficient for colistin resistance, but linked genes enhance this phenotype.
• mcr determinants modulate host phospholipid metabolism, impacting LPS modification and UPP homeostasis.
• hpap2 and dgkA likely contribute to colistin resistance by compensating for altered phospholipid metabolism.