The thymidylate kinase genes from Mycobacterium tuberculosis and methicillin-resistant Staphylococcus aureus confer 3′-azido-3′-deoxythymidine resistance to Escherichia coli

Abstract

The case number of invasive multidrug-resistant bacteria cultured from both hospital and community acquired infections is increasing at an alarming rate. Identifying the mechanisms bacteria use to escape the current antimicrobial treatments is essential to containing potential outbreaks and developing new antimicrobial therapies. Many bacteria naturally encode nonessential resistance genes on their chromosome enabling their survival and/or persistence in the presence of antibiotics using enzymes and efflux pumps. This study investigates the ability of an evolutionarily conserved essential gene to provide resistance against antimicrobial compounds. An Escherichia coli chromosomally encoded thymidylate kinase (tmk) conditional lethal strain was developed to investigate tmk alleles from relevant nosocomial pathogens. The thymidylate kinase conditional lethal strain harboring a plasmid with a tmk gene from Mycobacterium tuberculosis, methicillin-resistant Staphylococcus aureus (MRSA), or Pseudomonas aeruginosa downstream of an inducible promoter was examined for survival against increasing concentrations of 3′-azido-3′-deoxythymidine (AZT). The results indicate that M. tuberculosis and MRSA thymidylate kinases are deficient in cellular activity toward AZT monophosphate.