Methylglyoxal is an antibacterial effector produced by macrophages during infection.

Infected macrophages transition into aerobic glycolysis, a metabolic program crucial for controlling bacterial infection. However, antimicrobial mechanisms supported by aerobic glycolysis are unclear. Methylglyoxal is a highly toxic aldehyde that modifies proteins and DNA and is produced as a side product of glycolysis. We show that despite this toxicity, infected macrophages generate high levels of methylglyoxal during aerobic glycolysis while downregulating the detoxification system, including glyoxalase 1 (GLO1). Dampening methylglyoxal generation in mice resulted in enhanced survival of Listeria monocytogenes and Mycobacterium tuberculosis, whereas mice lacking Glo1 have increased methylglyoxal levels and improved infection control. Furthermore, bacteria unable to detoxify methylglyoxal (ΔgloA) exhibit attenuated virulence but are partially rescued in mice that cannot enter glycolysis and generate methylglyoxal. This loss of bacterial GloA results in up to a 1,000-fold greater genomic mutation frequency during infection. Collectively, these results suggest that methylglyoxal is an antimicrobial innate effector that defends against bacterial pathogens.