Phenotypic and molecular characteristics of carbapenem-resistant Enterobacteriaceae in a health care system in Los Angeles, California, from 2011 to 2013

Carbapenem-resistant Enterobacteriaceae (CRE) are a concern for health care in the United States but remain relatively uncommon in California. We describe the phenotype, clonality, and carbapenemase-encoding genes present in CRE isolated from patients at a Californian tertiary health care system. CRE for this study were identified by evaluating the antibiograms of Enterobacteriaceae isolated in the UCLA Health System from 2011 to 2013 for isolates that were not susceptible to meropenem and/or imipenem. The identification of these isolates was subsequently confirmed by matrix-associated laser desorption ionization-time of flight, and broth microdilution tests were repeated to confirm the CRE phenotype. Real-time PCR for bla_KPC, bla_SME, bla_IMP, bla_NDM-1, bla_VIM, and bla_OXA-48 was performed. Clonality was assessed by repetitive sequence-based PCR (repPCR) and multilocus sequence typing (MLST). Of 15,839 nonduplicate clinical Enterobacteriaceae isolates, 115 (0.73%) met the study definition for CRE. This number increased from 0.5% (44/8165) in the first half of the study to 0.9% (71/7674) in the second (P = 0.004). The most common CRE species were Klebsiella pneumoniae, Enterobacter aerogenes, and Escherichia coli. A carbapenemase-encoding gene was found in 81.7% (94/115) of CRE and included bla_KPC (78.3%), bla_NDM-1 (0.9%), and bla_SME (2.6%). The majority of bla_KPC genes were in K. pneumoniae isolates, which fell into 14 clonal groups on typing. bla_KPC was identified in more than one species of CRE cultured from the same patient in four cases. Three bla_SME-carrying Serratia marcescens isolates and one bla_NDM-1 carrying Providencia rettgeri isolate were detected. CRE are increasing in California, and carbapenemases, particularly KPC, are a common mechanism for carbapenem resistance in this region.