β-Lactam Antibiotics Targeting PBP1 Selectively Enhance Daptomycin Activity against Methicillin-Resistant Staphylococcus aureus

Abstract

The activity of daptomycin (DAP) against methicillin-resistant Staphylococcus aureus (MRSA) is enhanced in the presence of subinhibitory concentrations of antistaphylococcal ␤-lactam antibiotics by an undefined mechanism. Given the variability in the penicillin-binding protein (PBP)-binding profiles of different ␤-lactam antibiotics, the purpose of this study was to examine the relative enhancement of DAP activity against MRSA by different ␤-lactam antibiotics to determine if a specific PBP-binding profile is associated with the ability to enhance the anti-MRSA activity of DAP. We determined that both broad-and narrowspectrum ␤-lactam antibiotics known to exhibit PBP1 binding demonstrated potent enhancement of DAP anti-MRSA activity, whereas ␤-lactam antibiotics with minimal PBP1 binding (cefoxitin, ceftriaxone, cefaclor, and cefotaxime) were less effective. We suspect that PBP1 disruption by ␤-lactam antibiotics affects pathways of cell division in S. aureus that may be a compensatory response to DAP membrane insertion, resulting in DAP hypersusceptibility. The presence of subinhibitory concentrations of ␤-lactam antibiotics has been shown to increase daptomycin (DAP) activity against both DAP-susceptible and DAP-nonsusceptible (DNS) methicillin-resistant Staphylococcus aureus (MRSA) strains (1, 2). The mechanisms of this are not fully understood, but it has been attributed to a ␤-lactam-induced increase in the binding of DAP to bacterial cell membranes (3, 4). These observations fall in line with the observed DAP-␤-lactam "seesaw effect" whereby S. aureus frequently gains susceptibility to ␤-lactams upon the acquisition of the DNS phenotype (5). Collectively, these in vitro observations have been translated to antimicrobial therapy combinations to successfully manage difficult-to-treat MRSA infections (2, 3, 5, 6).Most in vivo studies have focused on three antistaphylococcal ␤-lactams, oxacillin, nafcillin (NAF), and ceftaroline, the latter because of its unique anti-MRSA properties among the ␤-lactam classes. However, no studies have compared the relative differences among the various ␤-lactam classes in their DAP-potentiating properties at therapeutically relevant concentrations.The potentiation of DAP activity obtained by the addition of a ␤-lactam antibiotic may provide a straightforward way to enhance anti-MRSA therapy against both DAP-susceptible and DNS MRSA. Achieving a bacteriostatic DAP area under the concentration-time curve (AUC)/MIC ratio against S. aureus (438 Ϯ 67) is challenging at a normal dose of 6 mg/kg (AUC ϭ 705 Ϯ 67) when the organism's DAP MIC is 2 g/ml or greater (7). Dose escalation to 8 or 10 mg/kg improves the likelihood of attaining this target parameter against strains with elevated MICs but results in a higher minimum drug concentration in serum (C min ), which has been associated with an increased risk of creatine phosphokinase elevation (8). High-dose DAP therapy is of particular concern in obese patients, where DAP AUCs are reported to be 30% greater than in nonobese matched co...

Penicillin Binding Protein 1 Is Important in the Compensatory Response of Staphylococcus aureus to Daptomycin-Induced Membrane Damage and Is a Potential Target for β-Lactam–Daptomycin Synergy

“…S. aureus strains D592 and D712 are paired isogenic MRSA isolates from a clinical series using DAP plus antistaphylococcal ␤-lactam in refractory bacteremia (3). Strain D592 is the DAP-susceptible index isolate, whereas D712 is a subsequent isolate that had become DNS as well as vancomycin intermediate following multiple unsuccessful antimicrobial regimens, as previously characterized (13). The genetic relatedness of the two patient isolates was confirmed by whole-genome sequencing (21).…”

“…The demonstrated effectiveness of this combination therapy despite heterogeneity in the specific ␤-lactam employed reflects the possibility that DAP-␤-lactam synergy may be a ␤-lactam class effect. However, a recent study observed significant diversity among different ␤-lactams in their relative efficacies in combination with DAP and reported that synergy is dependent on the relative affinity of a ␤-lactam for PBP1 (13).…”

“…The relative affinity of different ␤-lactams for PBPs varies: some ␤-lactams bind to and inactivate one PBP preferentially, while other ␤-lactams demonstrate relatively nonselective binding to multiple PBPs (11,12). Previous work has suggested that the degree to which different ␤-lactams potentiate the anti-MRSA activity of DAP may be associated with the relative affinity for PBP1 (13). This specific differential effect echoes other recent studies that observed increased toxin expression (12) and induction of DNA repair systems (14) upon inhibition of PBP1 but not upon inhibition of other PBPs (12,(15)(16)(17).…”

Treatment options for methicillin-resistant Staphylococcus aureus (MRSA) infection: Where are we now?

“…This may prevent the development of daptomycin resistance [96]. A recent article suggests that this benefit is particular for those b-lactams that bind to penicillin binding protein-1 (PBP1) [99].…”

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

“…We previously observed that DAP-mediated sensitization to ␤-lactams occurred with those ␤-lactams that preferentially target PBP 1 or PBP 2, including NAF (PBP 1, PBP 2), IPM (PBP 1), and CTX (PBP 2), whereas no changes were observed with ␤-lactams targeting PBP 4, such as cefoxitin (FOX), or PBP 3, such as cefaclor (CEC) (8,21,22). Similar effects were observed in other in vitro-selected DAP r mutants obtained from DAP s CB1631 (DAP r CB1631 mutants) and CB5011 (DAP r CB5011 mutants) (8).…”