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Colistin Resistance in KPC-2- and SHV-5-Producing Klebsiella pneumoniae Clinical Isolates in Bulgaria

Background/Aims: Colistin resistance is increasingly recognized among carbapenemase-producing Klebsiella pneumoniae isolates in several European regions. The current study documents the appearance of colistin resistance among KPC-2 and SHV-5-produning K. pneumoniae strains in Bulgaria. Methods: Four colistin-resistant K. pneumoniae isolates were recovered from 2 patients hospitalized in the anesthesiology and resuscitation clinic of a tertiary care university hospital in Sofia, Bulgaria. Microbial identification and antimicrobial susceptibility testing was performed by Vitek 2 (Biomerieux, France). β-Lactamase genes were amplified using a panel of primers for detection of all MBL-types, KPCs, plasmid-mediated AmpCs in single PCR reactions, OXA-type carbapenemases, extended-spectrum β-lactamases (ESBLs) and TEM enzymes. The colistin-resistant mcr-1 gene was also investigated using previously described primers and conditions. Pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) were used to investigate clonality. Results: The 4 K. pneumoniae isolates exhibited colistin MICs >16 mg/L and showed multidrug-resistant phenotypes, remaining intermediately susceptible only to gentamicin. They were clustered into a single PFGE clonal type and MLST assigned them to sequence type 258. All isolates possessed KPC-2 carbapenemase and SHV-5 ESBL. They were negative for the plasmid-mediated colistin-resistant mcr-1 gene, possibly implying an intrinsic mechanism of resistance. Conclusions: Although colistin use in Bulgaria only started moderately during 2014, the findings of the current study notify the appearance of colistin resistance among carbapenemase-producing Klebsiella species in another European region.