Activity of Meropenem with a Novel Broader-Spectrum β-Lactamase Inhibitor, WCK 4234, against Gram-Negative Pathogens Endemic to New York City.

WCK 4234 is a novel diazabicyclooctane with potent inhibitory activity against class A and D carbapenemases and class C enzymes. We examined the in vitro activity of meropenem plus WCK 4234 (4 or 8 μg/ml) against Gram-negative pathogens from New York City. Three groups of isolates were analyzed: a contemporary collection of isolates, a collection of known carbapenem-resistant isolates, and a collection of isolates with defined resistance mechanisms. From the contemporary collection, we found (i) that all Enterobacteriaceae were susceptible to meropenem plus WCK 4234, (ii) that susceptibility rates for Acinetobacter baumannii were 56.5% for meropenem alone, 82.6% with 4 μg/ml WCK 4234, and 95.7% with 8 μg/ml WCK 4234, and (iii) that WCK 4234 had a modest effect on susceptibility of Pseudomonas aeruginosa Against a collection of carbapenem-resistant isolates, the addition of WCK 4234 to meropenem (i) restored meropenem susceptibility against Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae isolates, (ii) improved susceptibility against A. baumannii, and (iii) had a negligible effect against P. aeruginosa When tested against isolates with defined mechanisms of resistance, MICs of meropenem plus WCK 4234 were higher for K. pneumoniae with bla KPC albeit well below the susceptibility breakpoint; efflux systems or porins did not correlate with susceptibility. For A. baumannii, MICs of meropenem plus WCK 4234 did not correlate with efflux systems, outer membrane protein, bla ampC, or bla oxa-51; however, MICs were higher in isolates with extended-spectrum β-lactamases (ESBLs). For P. aeruginosa, isolates with relatively higher MICs of meropenem plus WCK 4234 had increased expression of ampC WCK 4234 is a potent β-lactamase inhibitor that, when combined with meropenem, displays promising activity against multidrug-resistant pathogens.