Glutamine potentiates gentamicin to kill lab-evolved gentamicin-resistant and clinically isolated multidrug-resistant Escherichia coli

Valine potentiates cefoperazone-sulbactam to kill methicillin-resistant Staphylococcus aureus

Metabolic state-reprogramming approach was extended from Gram-negative bacteria to Gram-positive bacterium methicillin-resistant Staphylococcus aureus (MRSA) for identifying desired reprogramming metabolites to synergize existing antibiotic killing to MRSA. Metabolomics comparison between MRSA and methicillin-sensitive Staphylococcus aureus showed a depressed metabolic state in MRSA. Valine was identified as the most depressed metabolite/biomarker, and valine, leucine and isoleucine biosynthesis as the most enriched metabolic pathway. Thus, valine was used as a reprogramming metabolite to potentiate existing antibiotic killing to MRSA. Among the tested antibiotics, valine synergized cefoperazone-sulbactam (SCF) to produce the greatest killing effect. The combined effect of SCF and valine was demonstrated in clinical MRSA isolates and in mouse systemic and thigh infection models. Underlying mechanisms were attributed to valine-induced the activation of the pyruvate cycle/the TCA cycle and fatty acid biosynthesis. The activated pyruvate cycle/the TCA cycle elevated proton motive force by NADH and the activated fatty acid biosynthesis promoted membrane permeability by lauric acid. Both together increased cefoperazone uptake, which outpaces efflux action and thereby intracellular drug is elevated to effectively kill MRSA. These results provide the combination of valine and SCF to produce a new drug candidate effective against MRSA.

IMPORTANCE

Methicillin-resistant Staphylococcus aureus (MRSA) is possibly the most infamous example of antibiotic resistance and new antibiotics are urgently needed to control it. The present study used metabolic state-reprogramming approach to identify an ideal biomarker as an antibiotic adjuvant for reversing the metabolic state of MRSA. The most repressed valine was identified as the adjuvant. Exogenous valine most effectively potentiated cefoperazone-sulbactam (SCF) to kill MRSA in vitro and in vivo. Viability of 18 clinical MRSA isolates was reduced by the top 276.64-fold in the presence of valine and SCF. In mouse models, lower bacterial load in liver, spleen, kidney, thigh, and higher survival were determined in the SCF + valine than valine or SCF alone. Valine promoted MRSA to increase SCF uptake that overcomes the efflux and enzymatic hydrolysis. It also extended the PAE of SCF. These occur because valine activates the pyruvate cycle to elevate proton motive force by NADH and increases membrane permeability by lauric acid. Therefore, the combination of valine and SCF is a new drug candidate effective against MRSA.

Comparative Metabolomics Reveals Changes in the Metabolic Pathways of Ampicillin- and Gentamicin-Resistant Staphylococcus aureus

Antibiotic resistance is a major global challenge requiring new treatments and a better understanding of the bacterial resistance mechanisms. In this study, we compared ampicillin-resistant (R-AMP) and gentamicin-resistant (R-GEN) Staphylococcus aureus strains with a sensitive strain (ATCC6538) using metabolomics. We identified 109 metabolites; 28 or 31 metabolites in R-AMP or R-GEN differed from those in ATCC6538. Moreover, R-AMP and R-GEN were enriched in five and four pathways, respectively. R-AMP showed significantly up-regulated amino acid metabolism and down-regulated energy metabolism, whereas R-GEN exhibited an overall decrease in metabolism, including carbohydrate, energy, and amino acid metabolism. Furthermore, the activities of the metabolism-related enzymes pyruvate dehydrogenase and TCA cycle dehydrogenases were inhibited in antibiotic-resistant bacteria. Significant decreases in NADH and ATP levels were also observed. In addition, the arginine biosynthesis pathway, which is related to nitric oxide (NO) production, was enriched in both antibiotic-resistant strains. Enhanced NO synthase activity in S. aureus promoted NO production, which further reduced reactive oxygen species, mediating the development of bacterial resistance to ampicillin and gentamicin. This study reveals that bacterial resistance affects metabolic profile, and changes in energy metabolism and arginine biosynthesis are important factors leading to drug resistance in S. aureus.

Aminoglycoside uptake, stress, and potentiation in Gram-negative bacteria: new therapies with old molecules

SUMMARYAminoglycosides (AGs) are long-known molecules successfully used against Gram-negative pathogens. While their use declined with the discovery of new antibiotics, they are now classified as critically important molecules because of their effectiveness against multidrug-resistant bacteria. While they can efficiently cross the Gram-negative envelope, the mechanism of AG entry is still incompletely understood, although this comprehension is essential for the development of new therapies in the face of the alarming increase in antibiotic resistance. Increasing antibiotic uptake in bacteria is one strategy to enhance effective treatments. This review aims, first, to consolidate old and recent knowledge about AG uptake; second, to explore the connection between AG-dependent bacterial stress and drug uptake; and finally, to present new strategies of potentiation of AG uptake for more efficient antibiotic therapies. In particular, we emphasize on the connection between sugar transport and AG potentiation.

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

IMPORTANCE

Methicillin-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.

pts promoter influences antibiotic resistance via proton motive force and ROS in Escherichia coli

Introduction

Glucose level is related to antibiotic resistance. However, underlying mechanisms are largely unknown.

Methods

Since glucose transport is performed by phosphotransferase system (PTS) in bacteria, pts promoter-deleted K12 (Δpts-P) was used as a model to investigate effect of glucose metabolism on antibiotic resistance. Gas chromatography-mass spectrometry based metabolomics was employed to identify a differential metabolome in Δpts-P compared with K12, and with glucose as controls.

Results

Δpts-P exhibits the resistance to β-lactams and aminoglycosides but not to quinolones, tetracyclines, and macrolide antibiotics. Inactivated pyruvate cycle was determined as the most characteristic feature in Δpts-P, which may influence proton motive force (PMF), reactive oxygen species (ROS), and nitric oxide (NO) that are related to antibiotic resistance. Thus, they were regarded as three ways for the following study. Glucose promoted PMF and β-lactams-, aminoglycosides-, quinolones-mediated killing in K12, which was inhibited by carbonyl cyanide 3-chlorophenylhydrazone. Exogenous glucose did not elevated ROS in K12 and Δpts-P, but the loss of pts promoter reduced ROS by approximately 1/5, which was related to antibiotic resistance. However, NO was neither changed nor related to antibiotic resistance.

Discussion

These results reveal that pts promoter regulation confers antibiotic resistance via PMF and ROS in Escherichia coli.

A glucose-mediated antibiotic resistance metabolic flux from glycolysis, the pyruvate cycle, and glutamate metabolism to purine metabolism

Introduction

Bacterial metabolic environment influences antibiotic killing efficacy. Thus, a full understanding for the metabolic resistance mechanisms is especially important to combat antibiotic-resistant bacteria.

Methods

Isobaric tags for relative and absolute quantification-based proteomics approach was employed to compare proteomes between ceftazidime-resistant and -sensitive Edwarsiella tarda LTB4 (LTB4-RCAZ and LTB4-S, respectively).

Results

This analysis suggested the possibility that the ceftazidime resistance mediated by depressed glucose is implemented through an inefficient metabolic flux from glycolysis, the pyruvate cycle, glutamate metabolism to purine metabolism. The inefficient flux was demonstrated by the reduced expression of genes and the decreased activity of enzymes in the four metabolic pathways. However, supplement upstream glucose and downstream guanosine separately restored ceftazidime killing, which not only supports the conclusion that the inefficient metabolic flux is responsible for the resistance, but also provides an effective approach to reverse the resistance. In addition, the present study showed that ceftazidime is bound to pts promoter in E. tarda.

Discussion

Our study highlights the way in fully understanding metabolic resistance mechanisms and establishing metabolites-based metabolic reprogramming to combat antibiotic resistance.