Sergio Carrasco-Anabalón, Alejandra Vera-Leiva, Mario Quezada-Aguiluz, María F. Morales-Rivera, Celia A. Lima, Jorge Fernández, Soledad Ulloa, Mariana Domínguez, Gerardo González-Rocha, Helia Bello-Toledo
Abstract
Objective:
To elucidate whether the genetic platforms ofblaCTX-Mcontribute to the phenotypes of multi-drug-resistance (MDR) in the first carbapenemase-producingK. pneumoniaestrains isolated in Chile.Method:Twenty-two carbapenemase-producingK. pneumoniaestrains isolated from different Chilean patients and hospitals were studied. Their genetic relatedness was assessed by PFGE and MLST. The levels of antibiotic resistance were evaluated by determining the minimum inhibitory concentration of various antimicrobials. In addition, several antibiotic resistance genes of clinical relevance in Chile were investigated. The prevalence, allelic variants, and genetic platforms ofblaCTX-Mwere determined by PCR and sequencing.Results:Out of the 22 strains studied, 20 carry KPC, one carries NDM-1, and one carries OXA-370. The PFGE analysis showed three clades with a genetic relatedness >85%, two formed by four strains and one by eight strains. The other strains are not genetically related, and a total of 17 different pulse types were detected. Ten different STs were identified, the main ones being ST258 (five strains) and ST1161 (seven strains). The isolates presented different percentages of resistance, and 82% were resistant to all the β-lactams tested, 91% to ciprofloxacin, 73% to colistin, 59% to gentamicin, 50% to amikacin, and only 9% to tigecycline. All isolates carriedblaTEMandblaSHV, whereas 71% carriedaac(6')Ib-cr, and 57% oneqnrgene (A, B, C, D, orS). TheblaCTX-Mgene was found in 10 of the isolates (4blaCTX-M-15and 6blaCTX-M-2). The characterization of the platform, in seven selected strains, revealed that the gene is associated with unusual class 1 integrons and insertion sequences such as ISCR1, ISECp1, and IS26.Conclusion:In the first carbapenemase-producingK. pneumoniaestrains isolated in Chile the genetic platform ofblaCTX-M-2corresponds to an unusual class 1 integron that can be responsible for the MDR phenotype, whereas the genetic platforms ofblaCTX-M-15are associated with different IS and do not contribute to multi-drug resistance.
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