Molecular characterisation and epidemiology of extended-spectrum β-lactamase-producing Klebsiella pneumoniae isolates from immunocompromised patients in Tunisia.

Abstract

This study investigated the prevalence of extended-spectrum β-lactamase-producing Klebsiella pneumoniae (ESBL-KP) strains in the National Bone Marrow Transplant Center of Tunis between 2002 and 2011 as well as their associated antimicrobial resistance patterns and molecular features. Antimicrobial susceptibility was determined by the disk diffusion method according to CA-SFM guidelines. All of the strains were screened for β-lactamase genes, plasmid-encoded AmpC genes and integrons. Carbapenemase genes were analysed by PCR and sequencing for strains showing reduced susceptibility to ertapenem. Genetic relatedness was determined by pulsed-field gel electrophoresis (PFGE) and multilocus sequencing typing (MLST). A total of 128 non-repetitive ESBL-KP strains (23.4%) responsible for infection or colonisation were recovered among 548 K. pneumoniae strains. The isolates were also multidrug-resistant. Molecular analysis revealed the prevalence of blaSHV-type (92.2%), followed by blaOXA-1 (81.3%) and blaCTX-M-1 group (73.4%). Four ertapenem-resistant ESBL-KP strains (3.1%) carried the blaOXA-48 gene associated with the blaCTX-M-15 gene. Class 1 integrons were the most prevalent among the isolates (85.2%). High diversity was demonstrated by PFGE with limited clonal dissemination of 1 major (n=13 strains) and 11 minor clusters (each comprising 2-3 strains). MLST of representative strains also showed high diversity with two main epidemic clones: ST15, associated with the major cluster; and ST101, associated with five minor clusters (n=11 strains). This study provides relevant information on the epidemiology of ESBL-KP strains in oncohaematology patients, of which 18.8% belonged to the specific CTX-M-15 K. pneumoniae clones ST15 and ST101.