Epidemiologia molecolare di Klebsiella pneumoniae produttore di beta-lattamasi ad ampio spettro (ESBL) circolante in una Terapia Intensiva Neonatale

The molecular epidemiology of extended-spectrum beta-lactamase (ESBL)-producing Klebsiella pneumoniae was investigated in the neonatal intensive care unit (NICU) of a university hospital in Italy from September 2002 to December 2004, when 233 colonizations and 19 infections by K. pneumoniae occurred. Molecular typing by pulsed- field gel electrophoresis (PFGE) and dendrogram analysis of ESBL-producing K. pneumoniae isolates identified two distinct PFGE patterns B and C, that were sequentially isolated and that differed from one epidemic clone of PFGE type A isolated during 1996 in the same ward. Antimicrobial susceptibility patterns of ESBL-producing K. pneumoniae epidemic clones of PFGE type B and C showed an identical antibiotype, that differed from clone of PFGE type A for gentamicin resistance. DNA sequencing of amplified blaTEM and blaSHV genes resulted in the detection of a novel blaTEM ESBL gene, blaTEM-136, along with blaSHV-1 gene, in chromosomal and plasmid DNA from K. pneumoniae of PFGE type A, respectively, and blaTEM-1 and blaSHV-12 genes in chromosomal and plasmid DNA from K. pneumoniae epidemic clone of PFGE type B and C, respectively. Conjugation experiments demonstrated that resistance to third generation cephems, along with blaSHV-12 gene, was transferred from K. pneumoniae epidemic strains of PFGE type B and C to a susceptible E. coli host at a frequency of 4x 10-6 and 1 x 10-6 CFU/recipient cells, respectively. Our data suggest that the selection of ESBL producing clones and the transfer of blaSHV-12 ESBL gene between different clones were responsible for the spread of K. pneumoniae in the NICU.