RESUMEN
In this study, extended-spectrum ß-lactamase (ESBL)-producing Enterobacteriaceae isolates in children with malignancies hospitalised at a paediatric oncology department in the Czech Republic were investigated. From June 2009 to January 2010, a total of 50 ESBL-producing faecal isolates of Enterobacteriaceae were obtained from 28 patients. These isolates were characterised with regard to ESBL enzymes, plasmid-mediated quinolone resistance genes, multilocus sequence typing (MLST) and plasmids conferring resistance to cephalosporins and fluoroquinolones. ESBL-producing isolates included Klebsiella pneumoniae (n=36), Escherichia coli (n=7), Klebsiella oxytoca (n=3), Enterobacter cloacae (n=2) and Citrobacter freundii (n=2). Klebsiella pneumoniae isolates belonged to 7 MLST types, including sequence types ST280, ST321, ST323 and ST416 as well as the novel types ST626, ST627 and ST628. The multiresistant epidemic clone E. coli B2-O25b-ST131 was detected in one patient. The gene bla(CTX-M-15) was found on large conjugative IncFII(K) plasmids along with bla(TEM-1), bla(OXA-1), qnrB1, aac(6')-Ib-cr, strA, sul2, aac(3')-II and tet(A) genes in most isolates. Dissemination of IncFII(K) plasmids among various Enterobacteriaceae isolates was considered an important aspect of nosocomial colonisation in the wards by Enterobacteriaceae species producing ESBLs. This is the first study documenting multiple antibiotic resistance elements, including qnr genes, in IncFII(K) plasmids in various bacterial species isolated in a single hospital department. The results highlight the evolution of IncFII(K) plasmids into new variants containing novel antibiotic resistance elements and their important role in spreading ESBL-producing bacteria among hospitalised patients.