We aimed to investigate polymyxin B (PMB) resistance and its molecular mechanisms in 126 Klebsiella pneumoniae isolates from rectal swabs in Brazil. Ten isolates exhibited PMB resistance with interruption of mgrB gene by insertion sequences or missense mutations. Most of the PMB-resistant isolates harbored bla KPC-2 (n ‫؍‬ 8) and belonged to clonal complex 258 (CC258) (n ‫؍‬ 7). These results highlight the importance of monitoring the spread of polymyxin-resistant bacteria in hospitals, since few options remain to treat multidrug-resistant isolates. P olymyxin has been widely used to treat infections caused by multidrug-resistant (MDR) Gram-negative bacteria, including Klebsiella pneumoniae. However, reports of polymyxin-resistant K. pneumoniae (PRKP) isolates have increased worldwide, becoming a great public health concern (1).Most studies on PRKP have focused on patients with infections. However, there have been few reports assessing data on PRKP carriage in patients around the world (2). Some studies have described a remarkable and concerning number of patients who developed infection by PRKP after previous colonization, resulting in elevated mortality rates (3, 4). Colonization by KPCproducing K. pneumoniae and polymyxin therapy are considered important risk factors for PRKP infection (5, 6).Studies have demonstrated that modifications of PmrA/PmrB and PhoP/PhoQ two-component systems and inactivation of the mgrB gene (a regulator of the PhoP/PhoQ system) led to polymyxin resistance by modification of the lipopolysaccharide target (7). Recently, the plasmid-mediated transferable polymyxin resistance mcr-1 gene, causing resistance by modification of lipid A, was identified in China in Escherichia coli and K. pneumoniae strains (8).Here, we searched for molecular mechanisms associated with polymyxin resistance in K. pneumoniae isolates from Brazil. A first-step screening for polymyxin B (PMB) resistance was conducted using Etest (bioMérieux, France) in 126 isolates randomly selected from approximately 850 K. pneumoniae isolates with reduced susceptibility to carbapenems recovered from rectal swabs from 11 Brazilian states during 2007 to 2013. The bacterial identification was confirmed by conventional biochemical techniques. Considering the PRKP strains showing a MIC of Ͼ2.0 mg/liter (9), 10 (8%) PRKP isolates were observed and included in this study. These 10 PRKP isolates were collected between 2009 and 2013 from five Brazilian states (Fig. 1).To confirm the resistance phenotype, the PMB MIC was retested in duplicate by microdilution with cation-adjusted Mueller-Hinton broth (10). The isolates showed a MIC 50 of 64 mg/liter, a MIC 90 of Ͼ128 mg/liter, and a MIC range of 16 to Ͼ128 mg/liter (Table 1). Concordant Etest and microdilution results were found for only three isolates. The Etest MICs tended to be 1.3-fold to 4.0-fold lower than the microdilution MICs. Discrepancy between the two methodologies demonstrated that the Etest provided a

bEnzymes of the OXA-48 family have become some of the most important beta-lactamases in the world. A new OXA-48 variant (OXA-370) was first described for an Enterobacter hormaechei strain isolated in Rio Grande do Sul (southern region of Brazil) in 2013. Here we report detection of the bla OXA-370 gene in 24 isolates belonging to three Enterobacteriaceae species (22 Klebsiella pneumoniae isolates, 1 Enterobacter cloacae isolate, and 1 Enterobacter aerogenes isolate) collected from five hospitals in Rio de Janeiro, Brazil, in 2013 and 2014. The isolates showed a multidrug resistance profile, and 12.5% were resistant to polymyxin B. Besides bla OXA-370 , no other carbapenemase genes were observed by PCR, whereas bla OXA-1 was found in all isolates and 22 isolates (91.6%) possessed bla CTX-M-15 . Molecular typing of the K. pneumoniae isolates by pulsed-field gel electrophoresis (PFGE) showed the presence of two clonal groups, i.e., KpA (21 isolates) and KpB (1 isolate). KpA was characterized as sequence type 16 (ST16) and KpB as ST1041 by multilocus sequence typing (MLST). ST16 has been observed for KPC-producing K. pneumoniae in Rio de Janeiro. Plasmid analysis performed with six representative OXA-370-producing isolates showed plasmids harboring the bla OXA-370 gene in all strains, ranging from 25 kb to 150 kb. This study suggests that there is an urgent need to investigate the presence of OXA-370 and dissemination of the K. pneumoniae ST16 clone carrying this gene in Brazil.

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