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.

The detection and rapid spread of colistin-resistant Enterobacteriaceae carrying the mcr-1 gene has created an urgent need to strengthen surveillance. In this study, eight clonally unrelated colistin-resistant Escherichia coli isolates carrying mcr-1 and bla CTX-M or bla CMY-2 genes were isolated from commercial chicken meat in Brazil. Most E. coli strains carried IncX4 plasmids, previously identified in human and animal isolates. These results highlight a new reservoir of mcr-1-harboring E. coli strains in South America.

The emergence and rapid dissemination of colistin-resistant carrying the plasmid-mediated gene have created an urgent need to develop specific screening methods. In this study, we evaluated four assays based on the inhibition of MCR-1 activity by EDTA: (i) a combined-disk test (CDT) comparing the inhibition zones of colistin and colistin (10 μg) plus EDTA (100 mM); (ii) reduction of colistin MIC (CMR) in the presence of EDTA (80 μg/ml); (iii) a modified rapid polymyxin Nordmann/Poirel test (MPNP); and (iv) alteration of zeta potential (R = ZP/ZP). We obtained encouraging results for the detection of MCR-1 in isolates recovered from human, food, and animal samples, using the following assay parameters: ≥3 mm difference in the inhibition zones between colistin disks without and with EDTA; ≥4-fold colistin MIC decrease in the presence of EDTA; R of ≥2.5; and the absence of metabolic activity and proliferation, indicated by unchanged color of phenol red in the presence of colistin-EDTA, in the MPNP test. In this regard, the CDT, CMR, R, and MPNP assays exhibited sensitivities of 96.7, 96.7, 95.1, and 96.7% and specificities of 89.6, 83.3, 100, and 100%, respectively, for detecting MCR-1-positive Our results demonstrate that inhibition by EDTA and zeta potential assays may provide simple and inexpensive methods for the presumptive detection of MCR-1-producing isolates in human and veterinary diagnostic laboratories.

A colistin-resistant Escherichia coli strain was recovered from a patient with a diabetic foot infection in Brazil. Whole-genome analysis revealed that the E. coli isolate belonged to the widespread sequence type (ST) 101 and harbored the mcr-1 gene on an IncX4 plasmid that was highly similar to mcr-1-bearing IncX4 plasmids that were recently identified in Enterobacteriaceae from food, animal, and human samples recovered on different continents. These results suggest that self-transmissible IncX4-type plasmids may represent promiscuous plasmids contributing to the intercontinental spread of the mcr-1 gene.

The emergence and rapid spread of colistin-resistant Escherichia coli carrying the mcr-1 gene have generated an urgent need to strengthen surveillance. We performed a meticulous investigation of strains of this sort, which resulted in the identification of international clones of E. coli carrying IncX4-plasmid-mediated mcr-1 and bla CTX-M genes in recreational waters of public urban beaches in cities with high tourist turnover, highlighting a new environmental reservoir.KEYWORDS MCR-1, ESBL, CTX-M, IncX4, polymyxins, Brazil T he emergence and rapid spread of colistin-resistant Enterobacteriaceae carrying the mcr-1 gene have generated a profound sense of public alarm (1). Escherichia coli, one of the bacterial species that is most widely distributed and exchanged between the environment, animals, and humans, has been the main host of mcr-1 (2, 3). In South America, the occurrence of E. coli carrying mcr-1 and bla CTX-M genes in human (4-6) and wild animal (7) infections and food-producing animals (8) has created an urgent need to strengthen epidemiological surveillance. Using a whole-genome sequencing (WGS) approach, we performed a meticulous investigation of strains of this sort, which resulted in the identification of international clones of E. coli carrying mcr-1 and bla CTX-M-type genes in recreational waters of public urban beaches and highlighted a new source of transmission of this infectious threat.In September 2016, coastal water samples were collected from 11 different public beaches (in the southeastern Brazilian continental margin of São Paulo State) surrounding urban counties with a population of about 800,000 inhabitants, which can double during the summer. Following standard methods for the examination of water and wastewater (http://www.standardmethods.org), 500-ml surface water samples were collected, on the same day, in sterile bottles, transported to the laboratory in cooled containers (at about 4°C to 10°C), and processed within 6 h. From each water sample, 100 ml was concentrated by filtration through sterile membrane filters with a pore size of 0.45 m. The filters were placed on MacConkey agar plates and incubated for 24 h at 37°C. Next, the membrane filters were aseptically removed and placed separately in sterile tubes that had been filled previously with 10 ml of sterile Mueller-Hinton broth. After vortex mixing, an aliquot (100 l) of each culture was streaked on MacConkey agar plates supplemented with colistin (2 g/ml).Three colistin-resistant E. coli strains were recovered from different beaches located in the cities of São Vicente and Santos (Fig. 1); the latter is the major beachfront city of the region, with the largest shipping terminal in Latin America. The isolates were identified by matrix-assisted laser desorption ionization-time of flight mass spectrom-