In vitro activity of the β-lactamase inhibitor NXL104 against KPC-2 carbapenemase and Enterobacteriaceae expressing KPC carbapenemases

BACKGROUND: NXL104 is a novel-structure β-lactamase inhibitor with potent activity against both class A and class C enzymes. Among the class A carbapenemases, KPC-type enzymes are now spreading rapidly and KPC-related carbapenemase resistance is an emerging phenomenon of great clinical importance. The activity of NXL104 against KPC β-lactamases was examined. METHODS: Enzymatic activity of purified recombinant KPC-2 was measured with nitrocefin as reporter substrate and inhibition by NXL104 was measured by determination of IC(50) values. Antimicrobial susceptibility testing of various β-lactams combined with a fixed concentration of NXL104 at 4 mg/L against strains producing KPC enzymes was performed by the broth microdilution method. RESULTS: NXL104 was a potent inhibitor of KPC-2 with an IC(50) of 38 nM. NXL104 restored the antimicrobial activity of ceftazidime, ceftriaxone, imipenem and piperacillin against Enterobacteriaceae strains producing KPC-2 or KPC-3. MIC values of ceftazidime against KPC producers were reduced by up to 1000-fold by combination with NXL104. CONCLUSIONS: NXL104 inhibitory activity is unique in terms of spectrum, encompassing class A extended-spectrum β-lactamases, class C enzymes and class A carbapenemases. Given the limited therapeutic options available for infections caused by multiresistant Enterobacteriaceae isolates, NXL104 β-lactamase inhibitor is a promising agent to be used in combination with a β-lactam to protect its antibacterial activity.