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

Abstract

Background: 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.

Methods: 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. Results By in vitro testing, KPC-Kp isolates were highly resistant to all non-carbapenem beta-lactams (MIC(90)s >or= 128 mg/L). Among carbapenems, MIC(50/90)s 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 beta-lactamase extracts from these strains supported our findings, showing beta-lactamases at pIs of 5.4, 7.6 and 8.2. The mean number of beta-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.

Conclusions: We demonstrated the complex beta-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.

Figure 1

PFGE patterns of the 42 KPC-Kp isolates detected in five institutions located in the Eastern USA from January 2006 to October 2007 (MSMCNY, UPMC, UHCMC, CC, LSVAMC). Thirty-two isolates showed a genomic similarity >80% according to the Dice coefficient (type A). The remaining 10 isolates showed a similarity <80% when compared with type A isolates.

Figure 2

Genotype analysis of the 42 KPC-Kp isolates performed with the DiversiLab™ Strain Typing System (Bacterial BarCodes, bioMérieux). (a) rep-PCR results interpreted using the Pearson correlation. Twenty-five isolates (from #3 to #27) were included in a single genotype, whereas five (from #31 to #35) were included in another clone type. (b) rep-PCR results interpreted using the modified Kullback–Leibler method. A single major KPC-Kp clone was identified among the 42 isolates analysed. This figure appears in colour in the online version of JAC and in black and white in the print version of JAC.