engleski

Hidden carbapeneme resistance in OXA-48 positive E. coli

Abstract Background and aim OXA-48 hydrolyzes penicillins except of temocillin and carbapenems but spares expanded- spectrum cephalosporins. It is not inhibited by clavulanic acid, sulbactam or tazobactam. During 2016, 102 ESBL producing E. coli were collected in Slavonia region of Croatia in the frames of another study. Disk diffusion test revealed full susceptibility to all three carbapenems. However, seven ESBL producing organisms showed borderline ertapenem MIC (1 mg/L) in dilution test and were positive in CIM test and Hodge test. Unexpectedly, three of ertapenem nonsusceptibile isolates were shown to harbour A/C plasmid, previously associated with VIM or NDM MBLs. This finding prompted us to analzye the mechanisms of reduced susceptibility to ertapenem. Material and methods In this report, seven ertapenem non- susceptible E. coli originated from different anatomic sites were analyzed. The isolates were collected over 12 months period from patients hospitalized in GH Slavonski Brod, Slavonia region, Croatia.The susceptibility to a wide range of antibiotics was determined by disk- diffusion and broth microdilution method according to EUCAST standards and protocols.The transferability of cefotaxime resistance and reduced susceptibility to meropenem was determined by conjugation (broth mating method). The presence of blaCARB (bla KPC, blaVIM, blaIMP, blaNDM, blaOXA-48) and blaESBL genes (blaSHV, blaTEM, blaCTX-M) was determined by PCR and sequencing. PCR-based replicon typing (PBRT) was applied to determine the plasmid content of the tested isolates.PFGE genotyping of XbaI-digested genomic DNA was performed with CHEF-DRIII system (Bio-Rad) Results Isolates showed high level of resistance to expanded spectrum cephalosporins, gentamicin and ciprofloxacin. They were uniformly susceptible to colistin, amikacin, tigecycline and fosfomycin.. Disk diffusion and E-test showed susceptibility to ertapenem but dilution test yielded borderline MICs of 1 mg/L. All isolates were susceptibile to piperaicllin/tazobactam but showed variable levels of susceptibility/resistance to amoxycilllin/clavulanate. Hodge and CIM test were positive indicating the production of carbapenemase. All isolates transferred cefotaxime and meropenem resistance to E. coli recipient strain. The strains were shown to possess group 1 of CTX – M β-lactamase an d TEM – 1 in addition to OXA-48. BlaOXA-48 genes were preceeded by IS1999 whereas ISEcp was found upstream of blaCTX-M-15 genes in three isolates PFGE analysis revealed two clusters covering all seven isolates and containing subgroups of highly related isolates. Conclusions This report points to the need for determination of carbapenem MICs in E. coli ESBL positive isolates and additional testing for all isolates with borderline ertapenem MIC defined by EUCAST. The isolates showed the high level of resistance to expanded-spectrum cephalosporins due to the production of an additional ESBL belonging to CTX - M family. Unlike previous studies in Croatia, the dissemination of OXA - 48 in Slavonia region was associated with highly related isolates, belonging into two clusters.

Klebsiella pneumoniae ; OXA-48 ; carbapenems ; resistance

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