engleski

In vitro susceptibility of Klebsiella pneumoniae isolates producing extended-spectrum beta-lactamases (ESBL) from Zagreb to oral beta-lactams

The activity of oral beta-lactams against forty Klebsiella pneumoniae strains producing different types extended-spectrum beta-lactamases (ESBL) was studied. The susceptibility of the strains to various antibiotics was determined by disk-diffusion and broth microdilution method. ESBL production was detected by 8 fold reduction of ceftazidime/clavulanate MIC compared to ceftazidime alone. All strains were resistant to cefaclor and amoxycillin, 97.5% to cephalexin , 75% to cefuroxime and co-amoxyclav , 42.5% to ceftibuten and 27.5% to cefetamet. MIC90 of amoxycillin was >4096, of amoxycillin/clavulanic acid >1024, of cefaclor >1024, of cephalexin 1024, of cefuroxime >256 and of cefetamet and ceftibuten 32. The beta-lactamases were further characterized by isoelectric focusing in agarose gel and substrate profile determination. V_max was measured from crude extracts by macroiodometric method. 23 of 40 strains transferred ceftazidime resistance to E. coli recipient. Twelve K. pneumoniae strains and their E. coli transconjugants produced an ESBL with an isoelectric point of 8.2. Substrate profile was similar to that of SHV-5 beta-lactamase. An aditional TEM band was detected in six of these strains. Seven isolates and their transconjugants produced an ESBL derived from TEM beta-lactamases. The remaining 21 strains produced an ESBL with isoelectric point of 7.6 which was identified as SHV-2 based on isoelectric point and substrate profile. Four of those strains possessed an aditional TEM band. Strains producing SHV-5 type beta-lactamase expressed the highest level of resistance to oral beta-lactam antibiotics. The oral cephalosporins with a 7 beta-oxymino or vinyl side chain like cefuroxime, cefetamet and ceftibuten were more active than other (cephalexin and cefaclor).An inoculum effect was observed for all oral cephalosporins.

extended-spectrum beta-lactamases; Klebsiella pneumoniae; oral-beta-lactam antibiotics

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