LAUSR

Klebsiella pneumoniae is an important human pathogen, able to accumulate and disseminate a variety of antimicrobial resistance genes. Resistance to colistin, one of the last therapeutic options for MDR bacteria, has been increasingly reported. Colistin-resistant K. pneumoniae (ColRKp) emerged in two hospitals in Rio de Janeiro state, Brazil, in 2016. The aim of this study was to investigate if these ColRKp isolates were clonally related when compared between hospitals, to identify the molecular mechanisms of colistin resistance, and to describe other antimicrobial resistance genes carried by isolates. Twenty-three isolates were successively recovered, and 10 (each one of a PFGE type) had the whole-genome sequence analyzed. Although some PFGE clusters were found, no one included isolates from both hospitals. Half of the isolates were assigned to CC258, three to ST152 and two to ST15. One isolate was pandrug-resistant, one extensively drug-resistant, and the others multidrug-resistant. Colistin resistance was related to mutations in mgrB, pmrB, phoQ, and crrB. Eleven new mutations were found in these genes, including two nucleotide deletions in mgrB. All isolates were carbapenem resistant, seven of them associated with carbapenemase carriage, present in seven isolates (blaKPC-2 in 6, and blaOXA-370 in one). All isolates had a blaCTX-M, and two had a 16S ribosomal RNA methyltransferase encoding gene (armA and rmtB). ColRKp were composed of epidemic clones, but cross dissemination between hospitals was not detected. Colistin resistance emerged with several novel mutations amid highly resistant strains, further restricting the number of drugs available and leading to pandrug resistance.