Interaction of Ceftaroline with Clinically-Relevant β-Lactamases

Background: Ceftaroline fosamil is a cephalosporin approved for community-acquired pneumonia and acute bacterial skin and skin structure infections. Ceftaroline, the active metabolite of ceftaroline fosamil, has broad-spectrum in vitro activity against Gram-positive pathogens (including MRSA) and some Gram-negative organisms. To our knowledge, the hydrolysis of ceftaroline by clinically-relevant β-lactamases (BLs) has not been systematically studied. We thus investigated the hydrolytic activity of various BLs, including ESBLs, AmpC-type chromosomal and plasmid-mediated enzymes and serine- and metallo-carbapenemases, on ceftaroline and their potential contribution to ceftaroline resistance. Methods: Ceftaroline MICs were determined according to CLSI with isogenic laboratory E. coli strains producing representative BLs of class A (TEM-1, TEM-72, TEM-76, SHV-5, SHV-12, CTX-M-2, CTX-M-15, BEL-1, BEL-2, KPC-2), class B (IMP-1, IMP-18, VIM-2, NDM-1), class C (P. aeruginosa AmpC, E. cloacae AmpC, CMY-2, CMY-4) and class D (OXA-10, OXA-23, OXA-40, OXA-46, OXA-48) and compared to those of cephalothin, cefotaxime and ceftazidime. The kinetic parameters for the hydrolysis of these antibiotics by the 23 aforementioned purified BLs were determined by spectrophotometry. Results: All BLs efficiently hydrolyzed ceftaroline (kcat/Km ≥105 M-1.s-1), except TEM-76, BEL-2 and OXA-48. When compared to other tested cephalosporins, ceftaroline was hydrolyzed with similar (cephalothin and ceftriaxone) or higher (ceftazidime) efficiencies. Large differences in the individual kinetic parameters were observed, with turnover rates ranging 0.5 to 650 s-1. Class C enzymes and NDM-1 exhibited the lowest turnover rates for ceftaroline hydrolysis. Ceftaroline MICs for isogenic BL-producing E. coli strains ranged 0.12 to 256 µg/ml, most being resistant. Interestingly, the strains susceptible or intermediate to ceftaroline (according to CLSI criteria) were those producing AmpC, CMY-2, NDM-1 and OXA-48, characterized by low turnover rates (kcat ≤ 2 s-1). Conclusions: Although ceftaroline was readily hydrolyzed by most tested BLs, remarkable differences in turnover rates (3 orders of magnitude) were observed. The ceftaroline MIC data correlated with the kinetic parameters and showed that enzymes with low turnover rates were unable to confer ceftaroline resistance in an E. coli laboratory strain.