Carbapenem Resistance Caused by High-Level Expression of OXA-663 ß-Lactamase in an OmpK36-Deficient Klebsiella pneumoniae Clinical Isolate.

ABSTRACT

Carbapenem resistance is mainly mediated by carbapenemases or extended-spectrum ß-lactamases (ESBL) plus a loss of porins. However, we have identified a Klebsiella pneumoniae clinical isolate that contains neither carbapenemases nor ESBLs. Instead, we found that high-level expression of a novel blaOXA-10-derived ß-lactamase gene, blaOXA-663, in conjunction with OmpK36 deficiency results in high-level carbapenem resistance. This finding demonstrates the combinatorial complexity of factors, including ß-lactamase activity, its expression levels, and porin activity, that yield carbapenem resistance.