Epidemiology and molecular characterisation of colistin-resistant Klebsiella pneumoniae isolates from immunocompromised patients in Tunisia.

The aim of this retrospective study was to investigate the resistance determinants and genetic relatedness of colistin-resistant Klebsiella pneumoniae (ColR-Kp) isolates in the National Bone Marrow Transplant Center of Tunis (NBMTC) between 2002 and 2013. Minimum inhibitory concentrations (MICs) for colistin of ColR-Kp isolates were assessed using a UMIC broth microdilution kit. All isolates were screened by PCR for the resistance genes mcr-1, blaCTX-M-1, blaSHV, blaTEM, blaOXA-1, blaOXA-48, blaKPC, blaIMP, blaVIM, blaNDM, blaGES, blaIMI and blaAmpC as well as class 1, 2 and 3 integrons. The clonality of ColR-Kp isolates was investigated by pulsed-field gel electrophoresis (PFGE). A total of 24 non-duplicate ColR-Kp isolates were collected with MICs ranging from 16 mg/L to >64 mg/L, representing 3.4% (24/709) of the total K. pneumoniae isolates. The colistin resistance gene mcr-1 was not found. The blaSHV gene was present in all of the isolates, blaTEM in 18 isolates, blaCTX-M-1 and blaOXA-1 in 15 isolates each and blaCMY-16 in two isolates. The blaOXA-48 gene was found in five carbapenem-resistant isolates and was associated with blaCTX-M-1, blaSHV, blaTEM and blaOXA-1. All isolates were negative for the remaining carbapenemases. Class 1 integron was found in 19 isolates. PFGE showed non-clonal spread of ColR-Kp isolates in this center. The increasing rate of colistin resistance in K. pneumoniae isolates in NBMTC was neither associated to clonal diffusion nor to the plasmid-mediated colistin resistance gene mcr-1. Its association with the use of colistin in total digestive decolonization in transplant patients at NBMTC must be investigated.