L-glutamine sensitizes Gram-positive-resistant bacteria to gentamicin killing.

Because of the stubborn resistance to antibiotics, treating clinically resistant bacteria is a tricky business. Although considerable attention has been devoted to preventing and treating infections from drug-resistant bacteria, few studies are available on combining metabolites and antibiotics to combat methicillin-resistant Staphylococcus aureus (MRSA). This study found that exogenous L-glutamine potentiated aminoglycoside (gentamicin)-mediated killing efficacy in a dose- and time-dependent manner in MRSA (USA300 cell line) and other Gram-positive-resistant bacteria including MRSA 252, Listeria monocytogenes , and Corynebacterium diphtheriae . L-glutamine promoted the uptake of gentamicin through increasing the membrane permeability and was correlated with disrupted pH gradient. Furthermore, L-glutamine decreased intracellular reactive oxygen species by glutathione, which also increased USA300 sensitivity to gentamicin. We also demonstrated that combined treatment with gentamicin and L-glutamine enhanced the survival of MRSA-infected mice. In conclusion, we developed a promising therapeutic strategy for treating Gram-positive-resistant bacterial infections.IMPORTANCEMethicillin-resistant Staphylococcus aureus (MRSA) infection severely threatens human health due to high morbidity and mortality; it is urgent to develop novel strategies to tackle this problem. Metabolites belong to antibiotic adjuvants which improve the effect of antibiotics. Despite reports of L-glutamine being applied in antibiotic adjuvant for Gram-negative bacteria, how L-glutamine affects antibiotics against Gram-positive-resistant bacteria is still unclear. In this study, L-glutamine increases the antibacterial effect of gentamicin on MRSA, and it links to membrane permeability and pH gradient (ΔpH), resulting in uptake of more gentamicin. Of great interest, reduced reactive oxygen species (ROS) by glutathione was found under L-glutamine treatment; USA300 becomes sensitive again to gentamicin. This study not only offers deep understanding on ΔpH and ROS on bacterial resistance but also provides potential treatment solutions for targeting MRSA infection.