During a Brazilian multicentric antimicrobial resistance surveillance study, colistin resistance was investigated in 4,620 Enterobacteriaceae isolated from human, animal, food and environmental samples collected from 2000 to 2016. We present evidence that mcr-1-positive Escherichia coli has been emerging in South America since at least 2012, supporting a previous report on the possible acquisition of mcr-1-harbouring E. coli by European travellers visiting Latin American countries.

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T he rapid spread of the bla CTX-M-15 gene, which encodes the currently most widely distributed extended-spectrum ␤-lactamase (ESBL) enzyme in Gram-negative bacteria, is a global challenge to human and veterinary medicine. In this context, foodproducing animals have acquired an important role as reservoirs for CTX-M-15-producing bacteria, which can be transmitted to the community (1, 2). In this report, we describe for the first time the isolation of CTX-M-15-producing Escherichia coli in commercial swine in Brazil, highlighting a new reservoir of CTX-M-15-producing isolates with zoonotic potential in South America.In 2012, during a study conducted to assess the occurrence of ESBL-producing bacteria in swine production, eight (3%) ceftiofur-resistant CTX-M-15-producing E. coli isolates were recovered from 267 fecal swabs collected from male and female nursery (40 days) and finishing (90 days) pigs from 28 farms in seven Brazilian states. In this regard, ceftiofur-resistant strains were isolated by using MacConkey agar supplemented with 2 g/ml of ceftiofur. E. coli isolates were identified by the MALDI Biotyper (Bruker Daltonics, Germany), and the antibiotic resistance profiles were determined by the Kirby-Bauer method, with MICs determined by the microdilution technique by using Sensititre ESBL-confirmatory MIC plates (Trek Diagnostic Systems, Thermo Fisher) and/or the agar dilution method (3, 4). ESBL production was screened by the double-disk synergy test, and the presence of bla CTX-M -type genes was examined by PCR amplification and sequencing. E. coli isolates were further characterized by phylogenetic grouping (5) and multilocus sequence typing (MLST) (http: //mlst.warwick.ac.uk/mlst/dbs/Ecoli). Next, plasmids were extracted and used to transform electrocompetent E. coli TOP10 recipient cells (Invitrogen) by electroporation. The transformant E. coli TOP10 strains were selected on Mueller-Hinton agar supplemented with 2 g/ml of cefotaxime and further analyzed by replicon typing (6), plasmid MLST experiments (http://pubmlst .org/plasmid/), and partial plasmid sequencing to elucidate the bla CTX-M-15 genetic environment.The eight ceftiofur-resistant E. coli isolates produced CTX-M-15 and exhibited high MICs of human and veterinary cephalosporins (Table 1). Additionally, E. coli strains were resistant to ciprofloxacin, enrofloxacin, norfloxacin, tetracycline, sulfonamide-trimethoprim, and gentamicin (7). Otherwise, all isolates remained susceptible to amikacin, cephamycins, and carbapenems. The isolates belonged to three clonal lineages of sequence type (ST) 224 (5 strains from farm X in Minas Gerais State, southeastern Brazil), ST410 (CC23; 1 strain from farm Y in Minas Gerais State), and ST1284 (2 strains from farm Z in Paraná State, southern Brazil). While none of the eight isolates belonged to phylogroup B2, phylogroups A and B1 were identified among CTX-M-15-producing E. coli strains. For E. coli ST224 and ST410 strains, the bla CTX-M-15 gene was successfully transferred to TOP10 E. coli isolates by trans...

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