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 multi-drug resistant Klebsiella pneumoniae strains recovered from inpatients of public hospitals in the Mid-West of Brazil. METHODS 97 carbapenems non-susceptible K. pneumoniae were studied. β-lactamases ( bla OXA-48 , bla KPC , bla NDM , bla CTX-M , bla SHV , bla TEM , bla IMP , bla VIM ) 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 bla KPC (93.3%), bla SHV (86.6%), bla TEM (80.0%), bla CTX-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.

Introduction: Infections caused by multidrug-resistant Klebsiella pneumoniae are difficult to treat and pose a serious threat to public health worldwide. Here, we describe the presence of carbapenemase-producing K. pneumoniae in intensive care units (ICU) of three major Mato Grosso do Sul hospitals located in the Midwest region of Brazil. Methodology: A total of 165 K. pneumoniae isolates with reduced susceptibility to carbapenems as identified by the VITEK-2 compact system were studied. Antimicrobial susceptibility testing was performed using the disk diffusion method, as recommended by the Clinical and Laboratory Standards Institute, and the E-test method. The detection of carbapenemase was performed using the modified Hodge test and polymerase chain reaction. Results: The blaKPC gene was identified in 88.1% (n=89) of the selected K. pneumoniae isolates from Beneficent Association of Campo Grande, 94.9% (n=34) of the isolates from the Regional Hospital of Mato Grosso do Sul and 95.2% (n=26) of the isolates from Maria Aparecida Pedrossian University Hospital. Resistance greater than 80% was observed against cephalosporins, aztreonam, ciprofloxacin and piperacillin/tazobactam. Carbapenemase-producing K. pneumoniae (Kp-KPC) isolates were considered important causative agents of urinary tract infections, pneumonia and bloodstream infections in ICU patients. While rarely reported in the literature, we documented three cases of meningoencephalitis caused by Kp-KPC. Conclusions: Our study documents the presence of Kp-KPC in three major Mato Grosso do Sul state hospitals, providing key national epidemiology data. This is an important mechanism of resistance in K. pneumoniae isolates from ICU patients and is associated with resistance to multiple classes of antimicrobial drugs.