AUTHOR=Li Pingping , Shen Kai , Zhang Ying , Ying Jianchao , Zhu Tingyuan , Liu Yabo , Xu Lei , Lin Chaoqing , Zhang Kaibo , Li Peizhen , Lu Junwan , Li Kewei , Yi Huiguang , Bao Qiyu , Xu Teng 

TITLE=Characterization of a Novel blaKLUC Variant With Reduced β-Lactam Resistance From an IncA/C Group Plasmid in a Clinical Klebsiella pneumoniae Isolate

JOURNAL=Frontiers in Microbiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2018.01908

DOI=10.3389/fmicb.2018.01908

ISSN=1664-302X

ABSTRACT=<p>Similar to other CTX-M family enzymes, KLUC is a recently identified and emerging determinant of cefotaxime resistance that has been recovered from at least three <italic>Enterobacteriaceae</italic> species, including <italic>Kluyvera cryocrescens</italic>, <italic>Escherichia coli,</italic> and <italic>Enterobacter cloacae</italic>. Whether this extended-spectrum β-lactamase (ESBL) has been disseminated among commonly isolated <italic>Enterobacteriaceae</italic> is worthy of further investigation. In this study, we screened 739 nosocomial <italic>Enterobacteriaceae</italic> isolates (240 <italic>Klebsiella pneumoniae</italic> and 499 <italic>E. coli</italic> strains) and found that one <italic>K. pneumoniae</italic> and four <italic>E. coli</italic> isolates harbored the <italic>bla</italic><sub>KLUC</sub> gene. Three <italic>bla</italic><sub>KLUC</sub> determinants isolated from <italic>E. coli</italic> were entirely identical to a <italic>bla</italic><sub>KLUC-3</sub> gene previously recovered in the same hospital. PFGE of four <italic>bla</italic><sub>KLUC</sub>-harboring <italic>E. coli</italic> strains showed that prevalence of these determinants was most likely mediated by horizontal gene transfer but not clonal dissemination. However, the variant isolated from <italic>K. pneumoniae</italic> belonged to a novel member of the KLUC enzyme group. This newly identified enzyme (KLUC-5) has an amino acid substitution compared with previously identified KLUC-1 (G18S) and KLUC-3 (G240D). Antimicrobial susceptibility tests showed that KLUC-5 significantly reduced resistance activity to almost all the selected antimicrobials compared to previously identified KLUC-3. Site-directed mutagenesis showed that <italic>bla</italic><sub>KLUC-5</sub>-D240G and <italic>bla</italic><sub>KLUC-5</sub>-S18G significantly enhanced the MIC against its best substrate. Conjugation and S1-PFGE indicated that <italic>bla</italic><sub>KLUC-5</sub> was located on a transferable plasmid, which was further decoded by single-molecule, real-time sequencing. Comparative genome analysis showed that its backbone exhibited genetic homology to the IncA/C incompatibility group plasmids. A transposable element, IS<italic>Ecp1</italic>, was detected 256-bp upstream of the <italic>bla</italic><sub>KLUC-5</sub> gene; this location was inconsistent with the previously identified <italic>bla</italic><sub>KLUC-1</sub> but congruent with the variants recovered from <italic>E. coli</italic> in the same hospital. These data provide evidence of the increasingly emerging KLUC group of ESBLs in China.</p>