Molecular Bases Determining Daptomycin Resistance-Mediated Resensitization to β-Lactams (Seesaw Effect) in Methicillin-Resistant Staphylococcus aureus

Abstract

Antimicrobial resistance is recognized as one of the principal threats to public health worldwide, yet the problem is increasing. Infections caused by methicillin-resistant Staphylococcus aureus (MRSA) strains are among the most difficult to treat in clinical settings due to the resistance of MRSA to nearly all available antibiotics. The cyclic anionic lipopeptide antibiotic daptomycin (DAP) is the clinical mainstay of anti-MRSA therapy. The decreased susceptibility to DAP (DAP resistance [DAP r ]) reported in MRSA is frequently accompanied by a paradoxical decrease in ␤-lactam resistance, a process known as the "seesaw effect." Despite the observed discordance in resistance phenotypes, the combination of DAP and ␤-lactams has been proven to be clinically effective for the prevention and treatment of infections due to DAP r MRSA strains. However, the mechanisms underlying the interactions between DAP and ␤-lactams are largely unknown. In the study described here, we studied the role of mprF with DAP-induced mutations in ␤-lactam sensitization and its involvement in the effective killing by the DAP-oxacillin (OXA) combination. DAP-OXA-mediated effects resulted in cell wall perturbations, including changes in peptidoglycan insertion, penicillin-binding protein 2 (PBP 2) delocalization, and reduced membrane amounts of PBP 2a, despite the increased transcription of mecA through mec regulatory elements. We have found that the VraSR sensor-regulator is a key component of DAP resistance, triggering mutated mprF-mediated cell membrane (CM) modifications that result in impairment of PrsA location and chaperone functions, both of which are essential for PBP 2a maturation, the key determinant of ␤-lactam resistance. These observations provide for the first time evidence that synergistic effects between DAP and ␤-lactams involve PrsA posttranscriptional regulation of CM-associated PBP 2a.KEYWORDS MRSA, daptomycin, seesaw effect, ␤-lactams, PrsA, ␤-lactams S taphylococcus aureus has a proclivity for developing multidrug resistance (e.g., methicillin-resistant S. aureus [MRSA]), and infections with this pathogen result in enhanced attributable mortality (1). Since its FDA approval in 2003, the cyclic anionic lipopeptide antibiotic daptomycin (DAP), produced by Streptomyces roseosporus (2), has become the clinical mainstay of anti-MRSA therapy due to its potent staphylocidal

Bicarbonate Resensitization of Methicillin-ResistantStaphylococcus aureusto β-Lactam Antibiotics

“…In MRSA, there is a phenomenon somewhat akin to NaHCO 3 -β-lactam responsivity called the “see-saw” effect, in which MRSA cells that evolve daptomycin resistance become resensitized to β-lactams (50–53). This phenomenon involves the complex interaction between at least four genes.…”

“…This phenomenon involves the complex interaction between at least four genes. First , prsA is involved in the proper functioning of PBP2a by encoding a membrane-anchored chaperone required for proper PBP2a folding and insertion into the membrane (50, 51). Second, expression of prsA, in turn, is regulated by the two-component regulatory system, VraSR (52); in the see-saw effect, expression of vraSR is upregulated (50, 53).…”

“…First , prsA is involved in the proper functioning of PBP2a by encoding a membrane-anchored chaperone required for proper PBP2a folding and insertion into the membrane (50, 51). Second, expression of prsA, in turn, is regulated by the two-component regulatory system, VraSR (52); in the see-saw effect, expression of vraSR is upregulated (50, 53). Third, prsA expression is also co-regulated by gain-in-function mutations in the mprF operon which is involved in cell membrane phospholipid synthesis (54).…”

“…Third, prsA expression is also co-regulated by gain-in-function mutations in the mprF operon which is involved in cell membrane phospholipid synthesis (54). Of interest, in the see-saw effect, alteration of the cell membrane apparently prevents membrane insertion of PrsA, inhibiting this chaperone’s net functionality (50, 55). Fourth, expression of mprF is regulated by the sense-response two-component regulator, graRS (56), and is upregulated in daptomycin-resistant strains compared to daptomycin-susceptible strains (54, 57).…”

A FASII inhibitor prevents staphylococcal evasion of daptomycin by inhibiting phospholipid decoy production

“…A well-established example of this is the combination of daptomycin and β-lactams that target penicillin-binding protein (PBP) 1. In this combination, daptomycin sensitises MRSA to P-lactam antibiotics by reducing the quantity of PBP2a available, whilst β-lactams sensitise S. aureus to daptomycin by increasing binding of the lipopeptide antibiotic to the bacterial membrane [33-36]. This phenomenon, known as the see-saw effect, significantly promotes killing of S. aureus relative to each of the antibiotics individually and is currently being assessed as a therapeutic option in a clinical trial [37].…”