Mechanisms of resistance to third generation cephalosporins in Enterobacter spp

Sojevi bakterija vrste Enterobacter spp. su važni uzročnici bolničkih infekcija. Otpornost na antibiotike, posebice na cefalosporine treće generacije, je stalno u porastu. Otpornost može nastati zbog produkcije inducibilnih β-laktamaza, dereprimiranja kromosomskih β-laktamaza, uslijed produkcije β-laktamaza proširenog spektra (ESBL) ili zbog kombinacije navedenih mehanizama. U ovom diplomskom radu su se razjasnili mehanizmi otpornosti prikupljenih izolata na ispitivane antibiotike. Disk-difuzijskom metodom dokazan je porast otpornosti bakterija na cefalosporine treće generacije, što je potvrđeno metodom MIK. Cefoksitin-cefotaksim antagonističkim testom pokazano je da su svi izolati bili negativni na inducibilnost kromosomske AmpC β-laktamaze. Dvostrukim disksinergističkim testom pokazano je da su svi izolati bili ESBL pozitivni, što je potvrđeno CLSI testom. Svi izolati su bili pozitivni na hiperprodukciju kromosomske AmpC β- laktamaze, što je pokazano testom s bornom kiselinom. Modificiranim Hodge-ovim testom nađena su 2 soja producenta karbapenemaza. Metodom PCR ustanovljeno je da je 43% proučavanih sojeva proizvodilo β-laktamazu TEM, a 60% sojeva proizvodilo β- laktamazu CTX-M.Strains of Enterobacter spp. are important causes of nosocomial infections. Resistance to antibiotics, especially to third generation cephalosporins, is constantly increasing. Resistance can be mediated through production of inducible β-lactamases, derepressed chromosomal β-lactamases, extended spectrum β-lactamases (ESBL) or through combination of these mechanisms. The purpose of this research was to clarify the resistance mechanisms to antibiotics in question. Disk-diffusion method showed the rise of bacterial resistance to third generation cephalosporins, which was confirmed by MIC method. Cephoxitinecephotaxime antagonistic test showed that none of the isolates produced inducible chromosomal AmpC β-lactamases. Double disk-synergy test showed that all the isolates were ESBL positive, which was confirmed by CLSI test. All the isolates showed chromosomal AmpC β-lactamase hyperproduction, which was detected by boronic acid test. Modified Hodge test showed that two bacterial strains were producing carbapenemases. PCR method showed that 43% of the isolates was positive to TEM β- lactamase production and 60% of the isolates was positive to CTX-M β-lactamase production