Activity of Ceftaroline against Enterococcus faecium PBP5

Abstract

The opportunistic human pathogen Enterococcus faecium overproduces the low-affinity PBP5. In clinical strains, mutations in PBP5 further reduce its acylation rate by ␤-lactams. Previous studies have reported that ceftaroline had poor inhibitory activity against ␤-lactam-resistant E. faecium strains. In this study, we show that ceftaroline exhibits killing activity against our laboratory-derived ampicillin-resistant E. faecium mutant that overproduces a wild-type PBP5 and that ceftaroline inactivates PBP5 much faster than benzylpenicillin and faster than ceftobiprole. ␤ -Lactam antibiotics (penicillins, cephalosporins, carbapenems, and monobactams) represent the most important group of drugs prescribed to treat bacterial infections. They form stable acyl-enzymes with their targets, the membrane-bound D, D-transpeptidases, which are essential enzymes in peptidoglycan biosynthesis. These proteins are usually referred to as penicillin-binding proteins (PBPs) (1-3). The presence or overproduction of loweraffinity PBPs is responsible for the resistance of Gram-positive cocci against ␤-lactam antibiotics. It is known that the opportunistic human pathogen Enterococcus faecium overproduces the low-affinity PBP5 and that mutations further reduce the acylation rate of PBP5 by altering its amino acid sequence (4, 5). Ceftaroline is a cephalosporin with broad-spectrum activity against Grampositive organisms, including methicillin-resistant Staphylococcus aureus (MRSA), and many common Gram-negative bacteria except those producing extended-spectrum ␤-lactamase (ESBL) or AmpC ␤-lactamase (6-8). The Staphylococcus aureus low-affinity PBP2a is closely related to PBP5 (9). It is inhibited by ceftaroline, the active metabolite of the prodrug ceftaroline fosamil, which was recently approved by the U.S. Food and Drug Administration (FDA) for use in adult patients with acute bacterial skin and skinstructure infections and community-acquired bacterial pneumonia and more recently approved by the European Medicines Agency (EMA) for similar indications (10, 11). Previous studies have reported that ceftaroline had poor inhibitory activity against ␤-lactam-resistant E. faecium strains, all of which were expected to possess a PBP5 protein (6,12). To better understand these differences, we have characterized the interaction between a wild-type form of PBP5 and ceftaroline.Ceftaroline MIC values determined by the microdilution method (13) for E. faecium D63r and D63 strains (5) were 2 and 0.25 mg · liter Ϫ1 , respectively. These values contrasted with those reported by others (10-12), who have found that most ampicillinresistant E. faecium clinical isolates were resistant to ceftaroline and concluded that ceftaroline had little activity against most isolates of E. faecium. The killing effects (14) of ceftaroline on E. faecium D63 and D63r strains were studied by exposing exponentially growing cultures of both strains to increasing concentrations of antibiotics corresponding to 1 and 4 times their respective MICs (Fig. 1). Ceftaroline showed k...

β-Lactams Enhance Daptomycin Activity against Vancomycin-Resistant Enterococcus faecalis and Enterococcus faecium in In Vitro Pharmacokinetic/Pharmacodynamic Models

“…Recent data have also demonstrated that ceftobiprole is synergistic with DAP against VRE that are both DAP susceptible and DAP nonsusceptible (44). Previous work has demonstrated that ceftobiprole possesses activity against enterococcal PBP5 and PBPs 1 to 4 similar to, although not quite as potent as, that of CPT (40). These data further suggest the importance of PBP binding for synergistic DAP activity against enterococci.…”

“…In that study, the DAP-CRO combination was evaluated against E. faecium 8019, and the activity of that combination was similar to the activity we observed against 8019 with the DAP-CPT, DAP-ERT, and DAP-AMP combinations. CRO, however, possesses a narrower PBP binding profile than CPT (40). Based on the available data, it appears that there is an important combination of PBPs that should be bound for optimal DAP activity, and further study is needed to evaluate the optimal PBP binding profile for DAP enhancement.…”

“…In particular, resistant enterococci frequently possess an abundance of PBP5, a PBP with low affinity for ␤-lactams that allows survival in the presence of ␤-lactam therapy (39). CPT binds to this resistant PBP, possibly allowing enhanced DAP efficacy (40). In addition to its binding affinity for PBP5, CPT binds to enterococcal PBPs 1 to 4 more strongly than several other cephalosporins, perhaps suggesting that saturation of several PBPs, not only resistant PBP5, is important for synergistic activity.…”

Enterococcal Endocarditis Revisited

“…MICs of 1 and 2 mg/l, respectively. At 6 mg/kg, 9 of 11 (82%) and 11 of 12 (91%) culture-negative vegetations in rats infected with VanA and VanB type, respectively Levine et al (2007) [119] and ceftaroline were only effective for E. faecalis, but recent data insist that the former has in vitro activity against E. faecium with lowaffinity PBP 5, which confers a β-lactamase phenotype [190] and recent evidence showed that ceftaroline inactivates PBP5 even faster than ceftobiprole [191]. Besides, there are experimental data showing that the combination of beta-lactams (ceftaroline, ertapenem, ampicillin) with daptomycin is synergistic [192,193] and restores daptomycin activity in daptomycinnonsusceptible strains [194].…”

Evaluation of the in vitro activity of ceftobiprole against clinical isolates of Staphylococcus aureus

“…Similarly to other β-lactam antibacterial agents, ceftobiprole exerts its antibacterial activity by binding to important penicillin-binding proteins (PBPs) and inhibiting their transpeptidase activity (12), which is essential for the synthesis of the peptidoglycan layer of bacterial cell walls. Ceftobiprole binds to multiple PBPs in clinically relevant pathogens, which provides its broad activity spectrum (4,5,7,12,13). The anti-MRSA activity of ceftobiprole is attributed to its rapid and tight binding to the mutant PBP2a form (encoded by the mecA gene) that is able to confer resistance to methicillin and most β-lactam antibiotics (12).…”