Mechanisms of resistance to β-lactam antibiotics in gram-negative bacteria

Gram-negativne bakterije su uzročnici teških bolničkih infekcija, a posebice infekcija rana. Postoji stalan trend porasta učestalosti rezistencije na sve veći broj antibakterijskih lijekova koji uz druge činitelje rizika u hospitaliziranih bolesnika doprinose kolonizaciji i nastanku infekcija uzrokovanih multirezistentnim bakterijama. Cilj ovog rada bio je karakterizirati mehanizme rezistencije u izolatima bakterija Acinetobacter baumannii, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis i Pseudomonas aeruginosa, koje produciraju različite β-laktamaze, iz obrisaka rana. Utvrđena je produkcija β-laktamaza iz TEM, SHV i CTX-M porodice u enterobakteija. U jednom izolatu K. pneumoniae dokazano je prisustvo plazmidne AmpC β-laktamaze iz CMY porodice i VIM metalo-β-laktamaze. Svi izolati P. mirabilis pripadali su istom klonu i posjedovali blaTEM-52 gen. U svih izolata A. baumannii dokazana je insercijska sekvenca ISAba1 i svi su pripadali istom klonu. U izolata P. aeruginosa dokazana je niska stopa produkcije VIM metalo-β-laktamaza i svi su pripadali istom klonu. Niti u jednom izolatu nefermentativnih bakterija nije utvrđena rezistencija na kolistin. Ovi rezultati daju uvid u molekularnu epidemiologiju multirezistentnih bakterija i mogu doprinijeti kreiranju smjernica za empirijsku terapiju teških infekcija.Gram-negative bacteria are considered to be the most important pathogens causing serious nosocomial infections especially wound infections. The increasing resistance to numerous antibiotics together with other risk factors in hospitalized patients are contributing to development of multiresistant bacteria in recent years. The aim of this study was to determine the mechanisms of antibiotic resistance in: Acinetobacter baumannii, Enterobacter cloacae, Escherichia coli, Klebsiella pneumoniae, Proteus mirabilis and Pseudomonas aeruginosa isolated from wound swabs. ß-lactamases of TEM, SHV and CTX-M family were found in Enterobacteriaceae. Only one isolate of K. pneumoniae produced plasmid-mediated ß-lactamase of CMY family and metallo-β-lactamase of VIM family. All isolates of P. mirabilis harboured blaTEM-52 genes and were clonally related. A. baumannii isolates belonged to a single clone and harboured only blaOXA-51 gene upregulated by ISAba1. The low prevalence of VIM metal-β-lactamase was demonstrated in P. aeruginosa and all of them belonged to the same cluster. Resistance to colistin was not detected in nonfermentative bacteria. The results of this study will give a better insight into molecular epidemiology and enable to establish guidelines for the treatment of these infections