Characterization of blaKPC-containing Klebsiella pneumoniae isolates detected in different institutions in the Eastern USA

Abstract

The emergence of bla_KPC-containing Klebsiella pneumoniae (KPC-Kp) isolates is attracting significant attention. Outbreaks in the Eastern USA have created serious treatment and infection control problems. A comparative multi-institutional analysis of these strains has not yet been performed. We analysed 42 KPC-Kp recovered during 2006–07 from five institutions located in the Eastern USA. Antimicrobial susceptibility tests, analytical isoelectric focusing (aIEF), PCR and sequencing of bla genes, PFGE and rep-PCR were performed. By in vitro testing, KPC-Kp isolates were highly resistant to all non-carbapenem β-lactams (MIC₉₀s ≥ 128 mg/L). Among carbapenems, MIC_50/90s were 4/64 mg/L for imipenem and meropenem, 4/32 mg/L for doripenem and 8/128 for ertapenem. Combinations of clavulanate or tazobactam with a carbapenem or cefepime did not significantly lower the MIC values. Genetic analysis revealed that the isolates possessed the following bla genes: bla_KPC-2 (59.5%), bla_KPC-3 (40.5%), bla_TEM-1 (90.5%), bla_SHV-11 (95.2%) and bla_SHV-12 (50.0%). aIEF of crude β-lactamase extracts from these strains supported our findings, showing β-lactamases at pIs of 5.4, 7.6 and 8.2. The mean number of β-lactamases was 3.5 (range 3–5). PFGE demonstrated that 32 (76.2%) isolates were clonally related (type A). Type A KPC-Kp isolates (20 bla_KPC-2 and 12 bla_KPC-3) were detected in each of the five institutions. rep-PCR showed patterns consistent with PFGE. We demonstrated the complex β-lactamase background of KPC-Kp isolates that are emerging in multiple centres in the Eastern USA. The prevalence of a single dominant clone suggests that interstate transmission has occurred.