Outbreak of colistin-resistant carbapenemase-producing Klebsiella pneumoniae in Tunisia.

Objectives: Mechanisms of colistin and carbapenem resistance among a collection of Klebsiella pneumoniae isolates recovered in a university hospital in Tunisia were studied.

Methods: In vitro antimicrobial susceptibility testing, S1 nuclease pulsed-field gel electrophoresis (S1-PFGE), Southern blotting and PCR-based replicon typing (PBRT) were performed. Extended-spectrum β-lactamases (ESBLs), carbapenemases, AmpC-type enzymes and mgrB genes were detected by PCR and sequencing. Clonality of isolates was assessed by PFGE and multilocus sequence typing (MLST).

Results: Of 940 Enterobacteriaceae isolates recovered from June 2015 to March 2016 in Tahar Sfar Hospital (Mahdia, Tunisia), 220 were identified as K. pneumoniae, among which 29 were carbapenem-resistant. Carbapenem resistance was mostly due to expression of bla or bla in combination with bla. Seven isolates carried bla, of which two also harboured bla, together with bla in one of them. All but two isolates also harboured bla. All 20 bla genes were part of transposon Tn1999 on an IncL plasmid, whereas bla was found on transposon Tn2016 on an IncA/C plasmid. Finally, all bla genes were located within a Tn125 transposon on an IncFIIk plasmid. Interestingly, 7 (24.1%) of 29 carbapenem-resistant isolates were resistant to colistin, of which 6 were assigned to ST101, had similar PFGE profiles and presented the same 2-kb insertion in the mgrB gene.

Conclusions: This study reports, for the first time in Tunisia, the full molecular characterisation of colistin resistance in K. pneumoniae. There is an urgent need for control measures and prudent use of colistin in treatment of infections with carbapenemase-producing K. pneumoniae.