Effect of Resistance Mechanisms on the Inoculum Effect of Carbapenem in Klebsiella pneumoniae Isolates with Borderline Carbapenem Resistance

We aimed to examine the effects of resistance mechanisms on several resistance phenotypes among carbapenem-resistant Klebsiella pneumoniae isolates with borderline carbapenem MICs. We compared carbapenemase-negative K. pneumoniae with carbapenemase-producing K. pneumoniae (CPKP) isolates with similar MICs. CPKP isolates exhibited a marked inoculum effect and were more resistant to the bactericidal effect of meropenem. This suggests that MIC measurements alone may not be sufficient in predicting the therapeutic efficacy of carbapenems against CPKP.