Carbapenem Resistance in Klebsiella pneumoniae Not Detected by Automated Susceptibility Testing

Abstract

Detecting β-lactamase-mediated carbapenem resistance among Klebsiella pneumoniae isolates and other Enterobacteriaceae is an emerging problem. In this study, 15 bla KPC -positive Klebsiella pneumoniae that showed discrepant results for imipenem and meropenem from 4 New York City hospitals were characterized by isoelectric focusing; broth microdilution (BMD); disk diffusion (DD); and MicroScan, Phoenix, Sensititre, VITEK, and VITEK 2 automated systems. All 15 isolates were either intermediate or resistant to imipenem and meropenem by BMD; 1 was susceptible to imipenem by DD. MicroScan and Phoenix reported 1 (6.7%) and 2 (13.3%) isolates, respectively, as imipenem susceptible. VITEK and VITEK 2 reported 10 (67%) and 5 (33%) isolates, respectively, as imipenem susceptible. By Sensititre, 13 (87%) isolates were susceptible to imipenem, and 12 (80%) were susceptible to meropenem. The VITEK 2 Advanced Expert System changed 2 imipenem MIC results from >16 µg/mL to <2 µg/mL but kept the interpretation as resistant. The recognition of carbapenem-resistant K. pneumoniae continues to challenge automated susceptibility systems.

Characteristics and management of Enterobacteriaceae harboring IMP-4 or IMP-8 carbapenemase in a tertiary hospital

“…MICs derived by the Vitek 2 system were usually comparably low for imipenem and meropenem, whereas testing with microbroth dilution revealed higher MICs. This problem has been reported previously 33 . However, the Vitek 2 system is widely used in Chinese laboratories, and if included in the testing panel such as AST-GN13, ertapenem may serve as an indicator for the detection of IMP carbapenemase.…”

Molecular characterization of carbapenem-resistant Klebsiella pneumoniae isolates from a university hospital in Brazil

“…Some authors [38,39] have shown that some isolates with MICs for imipenem/meropenem within the susceptibility range can possess KPC enzymes, and then the detection of the carbapenemases may be difficult. In this study, all isolates were resistant to carbapenems, showing a MIC90 of 64 μg/mL for meropenem/imipenem and a MIC90 >128 μg/mL for ertapenem.…”

bla KPC RNA Expression Correlates with Two Transcriptional Start Sites but Not Always with Gene Copy Number in Four Genera of Gram-Negative Pathogens

“…Hydrolysis of carbapenems by KPCs has been demonstrated in vitro (1,21,22); however, multiple studies have reported variability in susceptibility testing of KPC-producing clinical isolates (2,3,13,22). Although variation in KPC enzyme production could contribute to the variability seen during susceptibility testing, it is difficult to assess the influence of the KPC ␤-lactamase on susceptibility testing using clinical isolates which may harbor multiple ␤-lactamases and may have alterations in outer membrane proteins (4,7,9,10,21,24). Therefore, we used cloning and transformation to create a panel of four different genera of Gram-negative bacteria that expressed the bla KPC gene without the influence of other resistance mechanisms.…”