Non-clonal occurrence of pmrB mutations associated with polymyxin resistance in carbapenem-resistant Klebsiella pneumoniae in Brazil.

BACKGROUND Polymyxins are currently used as a “last-line” treatment for multidrug-resistant Gram-negative infections. OBJECTIVES To identify the major mechanisms of resistance to polymyxin and compare the genetic similarity between multidrug resistant Klebsiella pneumoniae strains recovered from inpatients of public hospitals in the Mid-West of Brazil. METHODS 97 carbapenems non-susceptible K. pneumoniae w ere s tudied. β -lactamases ( blaOXA-48, blaKPC, blaNDM, blaCTX-M, blaSHV, blaTEM, blaIMP, blaVIM) and mcr-1 to mcr-5 genes were investigated by polymerase chain reaction (PCR). Mutations in chromosomal genes (pmrA, pmrB, phoP, phoQ, and mgrB) were screened by PCR and DNA sequencing. Clonal relatedness was established by using pulsed-field gel electrophoresis and multilocus sequence typing. FINDINGS K. pneumoniae isolates harbored blaKPC (93.3%), blaSHV (86.6%), blaTEM (80.0%), blaCTX-M (60%) genes. Of 15 K. pneumoniae resistant to polymyxin B the authors identified deleterious mutations in pmrB gene, mainly in T157P. None K. pneumoniae presented mcr gene variants. Genetic polymorphism analyses revealed 12 different pulsotypes. MAIN CONCLUSIONS Deleterious mutations in pmrB gene is the main chromosomal target for induction of polymyxin resistance in carbapenem-resistant K. pneumoniae in public hospitals in the Mid-West of Brazil.