Oxacillinases and antimicrobial susceptibility of Ralstonia pickettii from pharmaceutical water systems in Croatia.

This study evaluated antibiotic susceptibility and presence of blaOXA22 and blaOXA60 genes in 81 isolates of Ralstonia pickettii obtained from different purified and ultra-pure water systems in two different geographical areas of Croatia. E-test and disc diffusion test were performed to determine antibiotic susceptibility. Polymerase chain reaction was applied to detect genes encoding OXA-22 and OXA-60 oxacillinases previously identified in R. pickettii. The isolates were genotyped by pulsed-field gel electrophoresis. The results revealed variable susceptibility/resistance profiles. Our isolates exhibited high susceptibility rates to ceftriaxone, cefotaxime, piperacillin-tazobactam, ciprofloxacin, imipenem, cefepime and in lesser extent to ceftazidime. High rates of susceptibility were also observed for sulphamethoxazole-trimethoprim and piperacillin. High resistance rates were noticed for ticarcillin-clavulanate, aztreonam and meropenem, as well as for all aminoglycosides tested. Modified Hodge test was positive in 51·9% strains, indicating production of carbapenemases. blaOXA22 and blaOXA60 genes were detected in 37·0 and 80·3% strains, respectively. Pulsed-field gel electrophoresis identified three major clusters containing subclusters. R. pickettii should be taken seriously as a possible cause of nosocomial infections to ensure adequate therapy, to prevent the development of resistant strains and to try to reduce the possibility of R. pickettii surviving in clean and ultra clean water systems.

Epidemic and endemic spread of Klebsiella pneumoniae producing SHV-5 beta-lactamase in Dubrava University Hospital, Zagreb, Croatia.

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 parental TEM or SHV beta-lactamases. In a 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 K. pneumoniae strains in this hospital (20%) required further investigation. In this investigation, beta-lactamases from 42 K. 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, determination of hydrolysis of beta-lactam substrates, polymerase chain reaction and sequencing of bla(SHV) genes. All K. pneumoniae strains and their Escherichia coli transconjugants produced beta-lactamase with an isoelectric point of 8.2. Based on sequencing of bla(SHV) 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. In this study, an outbreak of nosocomial infections caused by SHV-5 producing K. pneumoniae was described in 1997 which evolved to endemic spread of SHV-5 producing K. pneumoniae due to multiple plasmid transfer in the Dubrava University Hospital. The strains from 1997 and 2004 were not clonally related. 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.