Thymine Sensitizes Gram-Negative Pathogens to Antibiotic Killing

Area of Science:

• Microbiology
• Infectious Diseases
• Pharmacology

Background:

• Antibiotic resistance in bacterial pathogens poses a significant global health threat.
• Bacterial metabolic state influences susceptibility to antibiotic treatments.
• The role of nucleotides as adjuvants with antibiotics against Gram-negative bacteria is largely unexplored.

Purpose of the Study:

• To investigate the potential of thymine as an adjuvant to potentiate antibiotic efficacy against Gram-negative pathogens.
• To elucidate the mechanisms by which thymine affects bacterial metabolism and antibiotic susceptibility.

Main Methods:

• Tested thymine in combination with bactericidal antibiotics (ciprofloxacin, ampicillin, kanamycin) against various Gram-negative bacteria.
• Assessed bacterial susceptibility in different growth phases.
• Analyzed metabolic changes including the tricarboxylic acid (TCA) cycle, respiration, adenosine triphosphate (ATP), and reactive oxygen species (ROS) production.
• Evaluated efficacy in a *Galleria mellonella* infection model.

Main Results:

• Thymine significantly enhanced the killing activity of ciprofloxacin against both sensitive and resistant *Escherichia coli* strains, independent of growth phase.
• Similar potentiation was observed with ampicillin and kanamycin against four different Gram-negative bacterial species.
• Exogenous thymine upregulated bacterial metabolism, increasing TCA cycle activity, respiration, ATP, and ROS production, thereby restoring antibiotic susceptibility.
• Thymine improved ciprofloxacin's efficacy in a *Galleria mellonella* infection model.

Conclusions:

• Thymine acts as a potent adjuvant, enhancing the activity of bactericidal antibiotics against Gram-negative pathogens.
• The mechanism involves the activation of bacterial metabolism, converting dormant bacteria into a more susceptible state.
• This finding presents a universal strategy to overcome antibiotic resistance in Gram-negative bacterial infections.