Genomic characterisation of a colistin-resistant Klebsiella pneumoniae ST11 strain co-producing KPC-2, FloR, CTX-M-55, SHV-12, FosA and RmtB causing a lethal infection.

Objectives: The aim of this study was to characterise the genomic and phenotypic characteristics of a colistin-resistant Klebsiella pneumoniae isolate causing a lethal infection that was phenotypically resistant to carbapenems and colistin.

Methods: Whole-genome sequencing was performed on an Illumina HiSeq 2500 platform. Genome annotation was performed by the Rapid Annotation using Subsystem Technology (RAST) server. Antimicrobial resistance genes and plasmid replicons were identified using ResFinder 2.1 and PlasmidFinder 1.3, respectively. The isolate was further characterised by plasmid analysis using S1-PFGE and Southern blot hybridisation with a digoxigenin-labelled probe specific for bla RESULTS: The genome of K. pneumoniae LSK16 consists of a 6.02-Mbp chromosome and one plasmid. Multilocus sequence typing (MLST) identified the isolate as ST11, a close variant of the international pandemic clone ST258. The isolate was found to harbour bla, bla, bla, floR and rmtB genes. Of note, a novel fosfomycin resistance glutathione transferase variant was confirmed by PCR and sequencing, with 98.6% (136/138) identity to fosA. Moreover, amino acid substitutions in PmrB (R256G) and PhoQ (D150G) were identified in LSK16, confirming the polymyxin/colistin resistance, although the isolate was negative for mcr genes. Southern blotting and plasmid analysis revealed that the bla gene was harboured on a non-conjugative IncR plasmid (˜165kb).

Conclusion: Here we identified a colistin-resistant K. pneumoniae ST11 strain co-producing KPC-2, FloR, CTX-M-55, SHV-12 and RmtB causing a lethal infection. This study provides new genomic insights into the diversity of K. pneumoniae ST11 prevalent in Zhejiang Province, China.