PBP2a Mutations Causing High-Level Ceftaroline Resistance in Clinical Methicillin-Resistant Staphylococcus aureus Isolates

Abstract

Ceftaroline is the first member of a novel class of cephalosporins approved for use in the United States. Although prior studies have identified eight ceftaroline-resistant methicillin-resistant Staphylococcus aureus (MRSA) isolates in Europe and Asia with MICs ranging from 4 to 8 mg/liter, high-level resistance to ceftaroline (>32 mg/liter) has not been described in MRSA strains isolated in the United States. We isolated a ceftaroline-resistant (MIC > 32 mg/liter) MRSA strain from the blood of a cystic fibrosis patient and five MRSA strains from the respiratory tract of this patient. Whole-genome sequencing identified two amino acid-altering mutations uniquely present in the ceftaroline-binding pocket of the transpeptidase region of penicillin-binding protein 2a (PBP2a) in ceftaroline-resistant isolates. Biochemical analyses and the study of isogenic mutant strains confirmed that these changes caused ceftaroline resistance. Thus, we identified the molecular mechanism of ceftaroline resistance in the first MRSA strain with high-level ceftaroline resistance isolated in the United States.

Clinical Laboratory Response to a Mock Outbreak of Invasive Bacterial Infections: a Preparedness Study

“…It has been used to identify unknown organisms, discover new mechanisms of antimicrobial resistance, and understand the virulence of isolates of uncertain taxonomic status (5,24). Whole-genome sequencing of microbes was previously validated in our molecular diagnostics laboratory, and it is run once per week as a routine clinical test.…”

Ceftobiprole- and Ceftaroline-Resistant Methicillin-Resistant Staphylococcus aureus

“…It is present in ceftobiprole-passaged COL (among other mutations) (11), it is the only mecA mutation in the ceftaroline-passaged SF8300, and it has been reported in clinical isolates (17,18). Structurally, E447 resides in the penicillin-binding domain of PBP2a and interacts with the R2 group of ceftobiprole and other ␤-lactams (3, 19).…”

Ceftaroline Activity against mecC -Containing Staphylococcus aureus

“…The major area of differentiation from other ␤-lactam drugs is the activity of ceftaroline (the active metabolite of ceftaroline fosamil) against MRSA, which is the result of improved affinity against the alternative penicillin-binding protein PBP2a (or MecA) that is also horizontally acquired on other SCCmec cassettes. However, substitutions in MecA have been linked to decreased susceptibility to ceftaroline, although those present in the non-penicillin-binding domain (nPBD) have less effect than those in the transpeptidase active site in the penicillin-binding domain (PBD) (6)(7)(8)(9)(10). During the genetic characterization of MRSA isolates collected during a 2012 surveillance program, a MRSA isolate (TRN6234) that contained a MecC protein identical to the protein encoded by LA-MRSA isolate LGA251 was identified from a patient in a German hospital with a serious wound infection (1).…”

“…The only other difference is the relatively conservative hydrophobic Y 446 F substitution. In MecA, this Y446 residue has been implicated in high-level resistance to ceftaroline, albeit as a polar Y 446 N substitution (8). This suggests that despite the high level of identity between the PBDs of these two alternative penicillin-binding proteins, subtle conformational differences which impact the binding mode of ceftaroline likely exist, and we await a cocomplex structure to interpret the differences.…”

“…This suggests that despite the high level of identity between the PBDs of these two alternative penicillin-binding proteins, subtle conformational differences which impact the binding mode of ceftaroline likely exist, and we await a cocomplex structure to interpret the differences. Furthermore, several of the residues in the nPBD that are often altered in MRSA isolates that have slightly decreased susceptibility to ceftaroline (MIC, 2 g/ml) are also not conserved in MecC (6,8,9). These include E239 and N146.…”