IMP-producing carbapenem-resistant Klebsiella pneumoniae in the United States

Abstract

The emergence and spread of carbapenem-resistant Enterobacteriaceae (CRE) producing acquired carbapenemases have created a global public health crisis. In the United States, CRE producing the Klebsiella pneumoniae carbapenemase (KPC) are increasingly common and are endemic in some regions. Metallo-β-lactamase (MBL)-producing CRE have recently been reported in the United States among patients who received medical care in countries where such organisms are common. Here, we describe three carbapenem-resistant K. pneumoniae isolates recovered from pediatric patients at a single U.S. health care facility, none of whom had a history of international travel. The isolates were resistant to carbapenems but susceptible to aztreonam, trimethoprim-sulfamethoxazole, and fluoroquinolones. The three isolates were closely related to each other by pulsed-field gel electrophoresis and contained a common plasmid. PCR and sequence analysis confirmed that these isolates produce IMP-4, an MBL carbapenemase not previously published as present among Enterobacteriaceae in the United States.

Fig. 1.

Phenotypic tests demonstrating metallo-β-lactamase production by a bla_IMP-positive K. pneumoniae isolate 1002003 (A and B) and bla_IMP-negative K. pneumoniae isolate 1002001 (C). (A) Modified Hodge test with meropenem demonstrating carbapenemase production by the test isolate and positive control but not the negative control. (B) Direct MBL test demonstrating subtle distortion of the zone of inhibition around the imipenem disk toward the EDTA disk and MBL Etest demonstrating deformation of the IP and IPI ellipses (arrow). (C) Example of negative results for the direct MBL test (round, undistorted zone of inhibition) and MBL Etest.

Fig. 2.

Dendrogram showing strain relatedness of bla_IMP-positive K. pneumoniae isolates compared to two contemporary bla_IMP-negative carbapenem-resistant K. pneumoniae isolates from California based on pulsed-field gel electrophoresis patterns. *, isolate did not produce an MBL.

Fig. 3.

XmnI digest and Southern blot analysis of plasmid DNA demonstrating presence of multiple plasmids in bla_IMP-positive K. pneumoniae isolates and a single plasmid in bla_IMP-positive E. coli transformants. Lane 1, E. cloacae bla_IMP positive control JMI10526; lane 2, E. cloacae bla_IMP negative control JMI03839; lane 3, K. pneumoniae 1000308; lane 4, E. coli transformant of 1000308; lane 5, K. pneumoniae 1002002; lane 6, E. coli transformant of 1002002; lane 7, K. pneumoniae 1002003; lane 8, E. coli transformant of 1002003; lane 9, HindIII digest of phage lambda DNA size standard. (A) Gel electrophoresis of plasmid DNA. (B) Southern blot analysis of DNA from the experiment shown in panel A with a bla_IMP-specific probe demonstrating presence of a single hybridizing band in both the parent and transformant strains.