Persistence of Klebsiella pneumoniae Producing SHV-5 beta-Lactamase in University Hospital, Zagreb.

Plasmid-encoded resistance to broad-spectrum cephalosporins and aztreonam is becoming a widespread phenomenon in clinical medicine. These antibiotics are inactivated by an array of different extended-spectrum beta-lactamases (ESBLs), which have evolved by point mutations of parenthal TEM or SHV beta-lactamases. In the previous study conducted during 1994-1995 SHV-2, SHV-2a and SHV-5 beta-lactamases were found among Klebsiella pneumoniae isolates in Dubrava University Hospital. High prevalence of ESBLs among Klebsiella pneumoniae strains in this hospital (20%) required further investigation. In this investigation, beta-lactamases from 42 Klebsiella pneumoniae strains collected in 1997 and 15 in 2004 from Dubrava University Hospital, were characterized in order to study the evolution of plasmid-encoded resistance to extended-spectrum cephalosporins and aztreonam in that hospital over a prolonged study period. Susceptibility to antibiotics was determined by disk-diffusion and broth microdilution method. beta-lactamases were characterized by isoelectric focusing, substrate profile determination, polymerase chain reaction and sequencing of blaSHV genes. All Klebsiella pneumoniae strains and their Escherichia coli transconjugants produced beta-lactamase with the isoelectric point of 8.2. Based on sequencing of blaSHV genes enzymes of all transconjugants were identified as SHV-5 beta-lactamase which conferred on the producing isolates high level of ceftazidime and aztreonam resistance. Most of the isolates have shown to be clonally related by pulsed-field gel electrophoresis. In this study, an outbreak of nosocomial infections caused by SHV-5 producing Klebsiella pneumoniae was described in 1997 which evolved to endemic spread of SHV-5 producing Klebsiella pneumoniae due to multiple plasmid transfer in the Dubrava University Hospital. In the previous study from 1994-1995, it was found that SHV-2 beta-lactamase, which is a cefotaximase according to the substrate profile, was the most prevalent type of ESBL in Dubrava Hospital, but in 1997 and 2004 it was completely replaced by SHV-5 beta-lactamase probably due selective pressure of ceftazidime which is the most widely prescribed expanded-spectrum cephalosporin in Croatian hospitals. Hospital hygiene measures should be applied in order to control the spread of epidemic strains through the hospital wards and the consumption of the broad-spectrum cephalosporins needs to be restricted to reduce the selection pressure which enables the proliferation of ESBL producers in hospital.