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 (Col-Kp) isolates in the National Bone Marrow Transplant Center of Tunis (NBMTC) between 2002 and 2013. Minimum inhibitory concentrations (MICs) for colistin of Col-Kp isolates were assessed using a UMIC broth microdilution kit. All isolates were screened by PCR for the resistance genes mcr-1, bla, bla, bla, bla, bla, bla, bla, bla, bla, bla, bla and bla as well as class 1, 2 and 3 integrons. The clonality of Col-Kp isolates was investigated by pulsed-field gel electrophoresis (PFGE). A total of 24 non-duplicate Col-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 bla gene was present in all of the isolates, bla in 18 isolates, bla and bla in 15 isolates each and bla in two isolates. The bla was found in five carbapenem-resistant isolates and was associated with bla, bla, bla and bla. All isolates were negative for the remaining carbapenemases. Class 1 integron was found in 19 isolates. PFGE showed non-clonal spread of Col-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.