Avaliação do EDTA na microdiluição em caldo com polimixina B como teste fenotípico para detecção do gene mcr-1

Abstract

Polymyxins are antibiotics that have recently regained significant interest as a consequence of the increasing infections due to multidrug-resistant Gram-negative bacteria. Currently, colistin and polymyxin B are used as last-line drugs for treating bacterial infections. However, polymyxin resistance has increased, and knowledge of its mechanisms is expanding. We aimed to evaluate the reduction of polymyxin MIC value based on the inhibition of the MCR-1 activity by the chelator ethylenediaminetetraacetic acid (EDTA) in the broth microdilution (BMD) method in presence of 2 mM. All mcr-1 positive isolates (n = 47) displayed a decrease in the MIC value for polymyxin B with the addition of EDTA, where 96% (n=45) displayed a decrease of at least 2-fold dilutions. Two mcr-1 positive isolates presented a decrease of only 1-fold dilution with EDTA. None of the mcr-1 negative (n = 28) isolates presented significant decrease in MIC values when the chelator was added to polymyxin B. Our results indicate that inhibition of MCR-1 by EDTA can be used for the presumptive detection of MCR-1-producing bacteria isolates when the BMD assay is applied.