Metabolic reprogramming and flux to cell envelope precursors in a pentose phosphate pathway mutant increases MRSA resistance to β-lactam antibiotics

Abstract

Central metabolic pathways controls virulence and antibiotic resistance, and constitute potential targets for antibacterial drugs. In Staphylococcus aureus the role of the pentose phosphate pathway (PPP) remains largely unexplored. Mutation of the 6-phosphogluconolactonase gene pgl, which encodes the only non-essential enzyme in the oxidative phase of the PPP, significantly increased MRSA resistance to β-lactam antibiotics, particularly in chemically defined media with glucose, and reduced oxacillin (OX)-induced lysis. Expression of the methicillin-resistance penicillin binding protein 2a and peptidoglycan architecture were unaffected. Carbon tracing and metabolomics revealed extensive metabolic reprogramming in the pgl mutant including increased flux to glycolysis, the TCA cycle, and several cell envelope precursors, which was consistent with increased β-lactam resistance. Morphologically, pgl mutant cells were smaller than wild-type with a thicker cell wall and ruffled surface when grown in OX. Further evidence of the pleiotropic effect of the pgl mutation was reduced resistance to Congo Red, sulfamethoxazole and oxidative stress, and increased resistance to targocil, fosfomycin and vancomycin. Reduced binding of wheat germ agglutinin (WGA) to pgl was indicative of lower wall teichoic acid/lipoteichoic acid levels or altered teichoic acid structures. Mutations in the vraFG or graRS loci reversed the increased OX resistance phenotype and restored WGA binding to wild-type levels. VraFG/GraRS was previously implicated in susceptibility to cationic antimicrobial peptides and vancomycin, and these data reveal a broader role for this multienzyme membrane complex in the export of cell envelope precursors or modifying subunits required for resistance to diverse antimicrobial agents. Altogether our study highlights important roles for the PPP and VraFG/GraRS in β-lactam resistance, which will support efforts to identify new drug targets and reintroduce β-lactams in combination with adjuvants or other antibiotics for infections caused by MRSA and other β-lactam resistant pathogens.

The Intersection between Bacterial Metabolism and Innate Immunity

“…A recent study with S. aureus serves as an intriguing example of the significant impact bacterial metabolism can have on antimicrobial susceptibility [140]. S. aureus is more resistant to β-lactam antibiotics when the nonessential gene, pgl , which encodes the pentose phosphate pathway enzyme 6-phosphogluconolactonase, is deleted [140].…”

“…A recent study with S. aureus serves as an intriguing example of the significant impact bacterial metabolism can have on antimicrobial susceptibility [140]. S. aureus is more resistant to β-lactam antibiotics when the nonessential gene, pgl , which encodes the pentose phosphate pathway enzyme 6-phosphogluconolactonase, is deleted [140]. The Δ pgl mutant does not induce the alternative penicillin-binding (PBP2a) that confers resistance to β-lactams [140, 141]; rather, the resistance phenotype is associated with a change in metabolism.…”

“…S. aureus is more resistant to β-lactam antibiotics when the nonessential gene, pgl , which encodes the pentose phosphate pathway enzyme 6-phosphogluconolactonase, is deleted [140]. The Δ pgl mutant does not induce the alternative penicillin-binding (PBP2a) that confers resistance to β-lactams [140, 141]; rather, the resistance phenotype is associated with a change in metabolism. The Δ pgl mutant redirects carbon flow to the production of cell wall precursors, ultimately changing cell envelope composition and increasing resistance to β-lactams [140].…”

“…The Δ pgl mutant does not induce the alternative penicillin-binding (PBP2a) that confers resistance to β-lactams [140, 141]; rather, the resistance phenotype is associated with a change in metabolism. The Δ pgl mutant redirects carbon flow to the production of cell wall precursors, ultimately changing cell envelope composition and increasing resistance to β-lactams [140]. The change in the cell envelope composition in the Δ pgl strain was mainly associated with reduced production of lipoteichoic acid (LTA).…”

“…One important observation from this study was that the choice of growth medium can significantly impact β-lactam sensitivity [140]. Bacteria grown in Mueller-Hinton had the highest levels of resistance, while growth in chemically defined media conferred intermediate resistance, and growth in chemically defined media supplemented with glucose had the least resistance [140].…”