Plasmidic resistance to colistin mediated by mcr-1 gene in Escherichia coli clinical isolates in Argentina: A retrospective study, 2012-2018.

OBJECTIVE: To describe the resistance profile and the genetic characteristics of Escherichia coli isolates that harbor the mobilizable colistin resistance gene mcr-1 in Argentina. METHODS: This was a retrospective study of 192 E. coli isolates positive for mcr-1 obtained from 69 hospitals of Buenos Aires City and 14 Argentinean provinces in 2012 - 2018. The antimicrobial susceptibility was performed by agar diffusion, broth macrodilution, and/or agar dilution. Standard polymerase chain reaction (PCR) was performed to detect resistance genes and incompatibility groups; specific PCR was applied to discriminate between blaCTX-M allelic groups and mcr-1.5 variant. The genetic relatedness among isolates was evaluated by XbaI-pulsed field gel electrophoresis and multilocus sequence typing in a subset of isolates. RESULTS: All E. coli isolates showed minimal inhibitory concentrations to colistin ≥ 4µg/mL; nearly 50% were resistant to third-generation cephalosporins, with CTX-M-2 being the main extended-spectrum ß-lactamase detected. Five E. coli were carbapenemase-producers (3 NDM, 2 KPC). The mcr-1.5 variant was detected in 13.5% of the isolates. No genetic relationship was observed among the mcr-1-positive E. coli clinical isolates, but a high proportion (164/192; 85.4%) of IncI2 plasmids was detected. CONCLUSIONS: The presence of IncI2 plasmids among highly diverse E. coli clones suggests that the mcr-1 gene's wide distribution in Argentina may be driven by the horizontal transmission of IncI2 plasmids.

qnrE1, a Member of a New Family of Plasmid-Located Quinolone Resistance Genes, Originated from the Chromosome of Enterobacter Species.

qnrE1, found in a clinical Klebsiella pneumoniae isolate, was undetectable by PCR assays used for the six qnr families. qnrE1 was located on a conjugative plasmid (ca. 185 kb) and differed from qnrB alleles by 25%. Phylogenetic reconstructions of qnr genes and proteins and analysis of the qnrE1 surroundings showed that this gene belongs to a new qnr family and was likely mobilized by ISEcp1 from the chromosome of Enterobacter spp. to plasmids of K. pneumoniae.

Rapid Identification of OXA-48 and OXA-163 Subfamilies in Carbapenem-Resistant Gram-Negative Bacilli with a Novel Immunochromatographic Lateral Flow Assay.

We assessed a novel immunochromatographic lateral flow assay for direct identification of OXA-48-like carbapenemases and accurate differentiation of allele variants with distinct substrate profiles (OXA-48 or OXA-163 subfamilies). The assay allowed rapid (less than 4 min) and reliable direct confirmation of OXA-163- and/or OXA-48-like enzymes (with 100% sensitivity and 100% specificity) from cultured colonies that were recovered from both solid medium and spiked blood culture bottles.

First report of abdominal sepsis caused by a recently described species: Chimaeribacter arupi.

We present a case of a 34-year-old patient with abdominal sepsis caused by an infrequent species: Chimaeribacter arupi. Genomic analysis confirmed the identification which is difficult to achieve by other methods so far. To our knowledge, this represents the first case of infection by this species reported in Argentina.

Phytobacter spp: the emergence of a new genus of healthcare-associated Enterobacterales encoding carbapenemases in Argentina: a case series.

Members of the genus Phytobacter (order Enterobacterales) are isolated from the natural environment and clinical settings. Identification of Phytobacter strains based on biochemical characteristics is complicated due to taxonomic confusion, and they are often misidentified by automated identification systems in laboratories. In this study we describe the first three clinical cases associated with Phytobacter spp. reported in Argentina. We describe the identification, the molecular analysis using whole genome sequencing and the potential clinical relevance.

Addressing pandemic-wide systematic errors in the SARS-CoV-2 phylogeny.

The SARS-CoV-2 genome occupies a unique place in infection biology - it is the most highly sequenced genome on earth (making up over 20% of public sequencing datasets) with fine scale information on sampling date and geography, and has been subject to unprecedented intense analysis. As a result, these phylogenetic data are an incredibly valuable resource for science and public health. However, the vast majority of the data was sequenced by tiling amplicons across the full genome, with amplicon schemes that changed over the pandemic as mutations in the viral genome interacted with primer binding sites. In combination with the disparate set of genome assembly workflows and lack of consistent quality control (QC) processes, the current genomes have many systematic errors that have evolved with the virus and amplicon schemes. These errors have significant impacts on the phylogeny, and therefore over the last few years, many thousands of hours of researchers time has been spent in "eyeballing" trees, looking for artefacts, and then patching the tree. Given the huge value of this dataset, we therefore set out to reprocess the complete set of public raw sequence data in a rigorous amplicon-aware manner, and build a cleaner phylogeny. Here we provide a global tree of 3,960,704 samples, built from a consistently assembled set of high quality consensus sequences from all available public data as of March 2023, viewable at https://viridian.taxonium.org. Each genome was constructed using a novel assembly tool called Viridian (https://github.com/iqbal-lab-org/viridian), developed specifically to process amplicon sequence data, eliminating artefactual errors and mask the genome at low quality positions. We provide simulation and empirical validation of the methodology, and quantify the improvement in the phylogeny. Phase 2 of our project will address the fact that the data in the public archives is heavily geographically biased towards the Global North. We therefore have contributed new raw data to ENA/SRA from many countries including Ghana, Thailand, Laos, Sri Lanka, India, Argentina and Singapore. We will incorporate these, along with all public raw data submitted between March 2023 and the current day, into an updated set of assemblies, and phylogeny. We hope the tree, consensus sequences and Viridian will be a valuable resource for researchers.

Emergence of Hyper-Epidemic Clones of Enterobacterales Clinical Isolates Co-Producing KPC and Metallo-Beta-Lactamases during the COVID-19 Pandemic.

BACKGROUND: The global spread of carbapenemase-producing Enterobacterales has become an epidemiological risk for healthcare systems by limiting available antimicrobial treatments. The COVID-19 pandemic worsened this scenario, prompting the emergence of extremely resistant microorganisms. METHODS: Between March 2020 and September 2021, the NRL confirmed 82 clinical Enterobacterales isolates harboring a combination of blaKPC and MBL genes. Molecular typing was analyzed by PFGE and MLST. Modified double-disk synergy (MDDS) tests were used for phenotypic studies. RESULTS: Isolates were submitted from 28 hospitals located in seven provinces and Buenos Aires City, including 77 K. pneumoniae, 2 K. oxytoca, 2 C. freundii, and 1 E. coli. Almost half of K. pneumoniae isolates (n = 38; 49.4%), detected in 15 hospitals, belong to the CC307 clone. CC11 was the second clone, including 29 (37.7%) isolates (22, ST11 and 7, ST258) from five cities and 12 hospitals. Three isolates belonging to CC45 were also detected. The carbapenemase combinations observed were as follows: 55% blaKPC-2 plus blaNDM-5; 32.5% blaKPC-2 plus blaNDM-1; 5% blaKPC-3 plus blaNDM-1; 5% blaKPC-2 plus blaIMP-8; and 2.5% strain with blaKPC-2 plus blaNDM-5 plus blaOXA-163. Aztreonam/avibactam and aztreonam/relebactam were the most active combinations (100% and 91% susceptible, respectively), followed by fosfomycin (89%) and tigecycline (84%). CONCLUSIONS: The MDDS tests using ceftazidime-avibactam/EDTA and aztreonam/boronic acid disks improved phenotypic classification as dual producers. The successful high-risk clones of K. pneumoniae, such as hyper-epidemic CC307 and CC11 clones, drove the dissemination of double carbapenemase-producing isolates during the COVID-19 pandemic.

Co-integrate Col3m bla NDM-1-harboring plasmids in clinical Providencia rettgeri isolates from Argentina.

The first cases of bla NDM in Argentina were detected in three Providencia rettgeri (Pre) recovered from two hospitals in Buenos Aires city in 2013. The isolates were genetically related, but the plasmid profile was different. Here, we characterized the bla NDM-1-harboring plasmids of the first three cases detected in Argentina. Hybrid assembly obtained from short- and long-read sequencing rendered bla NDM-1 in Col3M plasmids of ca. 320 kb (p15268A_320) in isolate PreM15268, 210 kb (p15758B_210) in PreM15758, and 225 kb (p15973A_225) in PreM15973. In addition, PreM15758 harbored a 98-kb circular plasmid (p15758C_98) flanked by a putative recombination site (hin-TnAs2), with 100% nucleotide ID and coverage with p15628A_320. Analysis of PFGE/S1-nuclease gel, Southern hybridization with bla NDM-1 probe, hybrid assembly of short and long reads suggests that pM15758C_98 can integrate by homologous recombination. The three bla NDM-1-plasmids were non-conjugative in vitro. Moreover, tra genes were incomplete, and oriT was not found in the three bla NDM-1-plasmids. In two isolates, blaNDM-1 was embedded in a partially conserved structure flanked by two ISKox2. In addition, all plasmids harbored aph(3')-Ia, aph(3')-VI, and qnrD1 genes and aac(6´)Ib-cr, bla OXA-1, catB3, and arr3 as part of a class 1 integron. Also, p15268A_320 and p15973A_225 harbored bla PER-2. To the best of our knowledge, this is the first report of clinical P. rettgeri harboring blaNDM-1 in an atypical genetic environment and located in unusual chimeric Col3M plasmids. The study and continuous surveillance of these pathogens are crucial to tracking the evolution of these resistant plasmids and finding solutions to tackle their dissemination. IMPORTANCE Infections caused by carbapenem hydrolyzing enzymes like NDM (New Delhi metallo-beta-lactamase) represent a serious problem worldwide because they restrict available treatment options and increase morbidity and mortality, and treatment failure prolongs hospital stays. The first three cases of NDM in Argentina were caused by genetically related P. rettgeri recovered in two hospitals. In this work, we studied the genetic structure of the plasmids encoding bla NDM in those index cases and revealed the enormous plasticity of these genetic elements. In particular, we found a small plasmid that was also found inserted in the larger plasmids by homologous recombination as a co-integrate element. We also found that the bla NDM plasmids were not able to transfer or move to other hosts, suggesting their role as reservoir elements for the acquisition of resistance genes. It is necessary to unravel the dissemination strategies and the evolution of these resistant plasmids to find solutions to tackle their spread.

Bactericidal killing of meningococcal W strains isolated in Argentina by the sera of adolescents and infants immunized with 4-component meningococcal serogroup B vaccine (4CMenB).

Invasive meningococcal disease (IMD) is a life-threatening disease caused by meningococcal serogroups A, B, C, W, X, and Y, of which B and W are most common in Argentina. The 4-component meningococcal serogroup B (4CMenB) vaccine contains three purified recombinant protein antigens (Neisseria adhesin A [NadA], factor H binding protein [fHbp], and Neisserial Heparin Binding Antigen [NHBA]) and outer membrane vesicles (OMV), which is derived from the New Zealand epidemic strain and contains Porin A 1.4. These antigens are present and conserved in strains that belong to other serogroups. In this study, we show that 10/11 (91%) meningococcal serogroup W (MenW) strains selected to be representative of MenW isolates that caused IMD in Argentina during 2010-2011 were killed in bactericidal assays by the sera of adolescents and infants who had been immunized with the 4CMenB vaccine. We also show that MenW strains that caused IMD in Argentina during 2018-2021 were genetically similar to the earlier strains, indicating that the 4CMenB vaccine would likely still provide protection against current MenW strains. These data highlight the potential of 4CMenB vaccination to protect adolescents and infants against MenW strains that are endemic in Argentina.

Carbapenemase-Producing Extraintestinal Pathogenic Escherichia coli From Argentina: Clonal Diversity and Predominance of Hyperepidemic Clones CC10 and CC131.

Extraintestinal pathogenic Escherichia coli (ExPEC) causes infections outside the intestine. Particular ExPEC clones, such as clonal complex (CC)/sequence type (ST)131, have been known to sequentially accumulate antimicrobial resistance that starts with chromosomal mutations against fluoroquinolones, followed with the acquisition of bla CTX-M-15 and, more recently, carbapenemases. Here we aimed to investigate the distribution of global epidemic clones of carbapenemase-producing ExPEC from Argentina in representative clinical isolates recovered between July 2008 and March 2017. Carbapenemase-producing ExPEC (n = 160) were referred to the Argentinean reference laboratory. Of these, 71 were selected for genome sequencing. Phenotypic and microbiological studies confirmed the presence of carbapenemases confirmed as KPC-2 (n = 52), NDM-1 (n = 16), IMP-8 (n = 2), and VIM-1 (n = 1) producers. The isolates had been recovered mainly from urine, blood, and abdominal fluids among others, and some were from screening samples. After analyzing the virulence gene content, 76% of the isolates were considered ExPEC, although non-ExPEC isolates were also obtained from extraintestinal sites. Pan-genome phylogeny and clonal analysis showed great clonal diversity, although the first phylogroup in abundance was phylogroup A, harboring CC10 isolates, followed by phylogroup B2 with CC/ST131, mostly H30Rx, the subclone co-producing CTX-M-15. Phylogroups D, B1, C, F, and E were also detected with fewer strains. CC10 and CC/ST131 were found throughout the country. In addition, CC10 nucleated most metalloenzymes, such as NDM-1. Other relevant international clones were identified, such as CC/ST38, CC155, CC14/ST1193, and CC23. Two isolates co-produced KPC-2 and OXA-163 or OXA-439, a point mutation variant of OXA-163, and three isolates co-produced MCR-1 among other resistance genes. To conclude, in this work, we described the molecular epidemiology of carbapenemase-producing ExPEC in Argentina. Further studies are necessary to determine the plasmid families disseminating carbapenemases in ExPEC in this region.

Characterization of the First mecA-Positive Multidrug-Resistant Staphylococcus pseudintermedius Isolated from an Argentinian Patient.

Staphylococcus pseudintermedius is commonly associated with colonization or infection in dogs, and was identified as a novel species within the genus Staphylococcus in 2006. Methicillin resistance emerged in S. pseudintermedius during the last decade. We describe here a genomic characterization of the first methicillin-resistant S. pseudintermedius (MRSP) recovered from a human patient in Argentina. The strain was phenotypically identified as MRSP 8510 by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF MS) and antimicrobial susceptibility testing. We assessed genetic characterization by mecA PCR, SCCmec (staphylococcal chromosomal cassette) typing, and whole-genome sequencing. MRSP 8510 was phenotypically resistant to six classes of antimicrobial agents, consistent with the genes found in its genome. We concluded that MRSP 8510 was a multidrug-resistant ST1412 isolate. This study highlights the importance of the detection and characterization of pathogens with potential risks of zoonotic transmission to humans, as they may constitute a reservoir of genes associated with antimicrobial resistance.

Comparative Kinetic Analysis of OXA-438 with Related OXA-48-Type Carbapenem-Hydrolyzing Class D ß-Lactamases.

Novel variants of OXA-48-type enzymes with the ability to hydrolyze oxyimino-cephalosporins and carbapenems are increasingly reported. Since its first report in 2011, OXA-163 is now extensively spread throughout Argentina, and several variants like OXA-247 have emerged. Here, we characterized a new blaOXA-48-like variant, OXA-438, and we performed a comparative kinetic analysis with the local variants OXA-247 and OXA-163 and the internationally disseminated OXA-48. blaOXA-163, blaOXA-247, and blaOXA-438 were located in a 70 kb IncN2 conjugative plasmid. OXA-438 presented mutations in the vicinity of conserved KTG (214-216), with a 2-aa deletion (R220-I221) and a D224E shift (as in OXA-163) compared to OXA-48. Despite Kpn163 (OXA-163), Kpn247 (OXA-247) and Eco438 (OXA-438) were resistant to meropenem and ertapenem, and the transconjugants (TC) remained susceptible (however, the carbapenems minimum inhibitory concentrations were ≥3 times 2-fold dilutions higher than the acceptor strain). TC163 and Eco48 were resistant to oxyimino-cephalosporins, unlike TC247 and TC438. kcat/Km values for cefotaxime in OXA-163 were slightly higher than the rest of the variants that were accompanied by a lower Km for carbapenems. For OXA-163, OXA-247, and OXA-438, the addition of NaHCO3 improved kcat values for both cefotaxime and ceftazidime; carbapenems kcat/Km values were higher than for oxyimino-cephalosporins. Mutations occurring near the conserved KTG in OXA-247 and OXA-438 are probably responsible for the improved carbapenems hydrolysis and decreased inactivation of oxyimino-cephalosporins compared to OXA-163. Dichroism results suggest that deletions at the ß5-ß6 loop seem to impact the structural stability of OXA-48 variants. Finally, additional mechanisms are probably involved in the resistance pattern observed in the clinical isolates.

Multiple clones of metallo-ß-lactamase-producing Acinetobacter ursingii in a children hospital from Argentina.

Acinetobacter spp. are opportunistic pathogens being A. baumannii the most frequently identified in nosocomial settings. A. ursingii was mainly described as causing bacteremia and outbreaks in neonatal intensive care units. Ten A. ursingii isolates were recovered from rectal swab screening for carbapenemase-producing bacteria between June 2013 and December 2015 from a children hospital in Argentina. All ten isolates were metallo-ß-lactamase-producing, nine were positive for blaIMP-1 and one for blaNDM-1. IMP-positive isolates were also positive for blaOXA-58 gene. All isolates were susceptible to ciprofloxacin, colistin and minocycline, and nine were susceptible to ampicillin-sulbactam and gentamicin. Two A. ursingii displayed high level of resistance to aztreonam associated with blaCTX-M-15 in one isolate, and blaVEB-1 in the other. Eight SmaI-PFGE patterns were recognized. We evaluated the usefulness of Acinetobacter MLST-Pasteur scheme, to analyse A. ursingii isolates, however the rpoB gene was not amplified. A new set of primers were designed for specific amplification and sequencing, allowing the analysis of rpoB gene for this species. New alleles and the sequence types 748, 749, 750, 751, 993, 1186, 1187, and 1189 were included at the Acinetobacter MLST-Pasteur database. Those isolates showing related PFGE patterns were assigned to the same ST. To the best of our knowledge, this is the first report of MBL-producing A. ursingii in Argentina. The inclusion of A. ursingii species to the Acinetobacter MLST-Pasteur scheme allows deeper molecular characterization and a better understanding about the epidemiology of this germen.

Genetic Diversity of KPC-Producing Escherichia coli, Klebsiella oxytoca, Serratia marcescens, and Citrobacter freundii Isolates from Argentina.

The predominance of Klebsiella pneumoniae carbapenemase (KPC)-producing K. pneumoniae was caused by the spread of ST258 clone. In Latin America, KPC was reported in 2006, with the isolation of genetically unrelated K. pneumoniae in Colombia. Since then, the expansion of blaKPC in either K. pneumoniae ST258 or other Enterobacteriaceae (ETB) species was increasingly reported. In this study, we characterized 89 KPC-producing Escherichia coli, Klebsiella oxytoca, Serratia marcescens, and Citrobacter freundii that were received between 2010 and 2014. The results revealed that all isolates harbored blaKPC-2. Moreover, the dissemination of KPC by non-K. pneumoniae was mainly caused by the dispersion of ETB mostly genetically unrelated. E. coli is a community pathogen that may serve as the vehicle for the spread of KPC into community settings. Recently, KPC was detected in E. coli ST131, an international epidemic and multidrug-resistant clone. We found that 5/29 KPC-producing E. coli belonged to ST131 and four were blaCTXM-15 producers. The detection of blaKPC in ST131 should be closely monitored to prevent further dissemination. The blaKPC is generally located within Tn4401 transposon capable of mobilization through transposition found in plasmids in ST258. Less is known about the diversity of blaKPC genetic elements that disseminate horizontally among other species of ETB. We found that 16/29 E. coli and 2/18 S. marcescens harbored blaKPC-2 in Tn4401a. In 71 isolates, blaKPC-2 was located amidst diverse Tn3-derived genetic elements bearing non-Tn4401 structure. Further studies on the plasmids that encode blaKPC-2 in these clinical isolates may provide additional insight into its transmission mechanisms.

Plasmidic resistance to colistin mediated by mcr-1 gene in Escherichia coli clinical isolates in Argentina: A retrospective study, 2012–2018

[ABSTRACT]. Objective. To describe the resistance profile and the genetic characteristics of Escherichia coli isolates that harbor the mobilizable colistin resistance gene mcr-1 in Argentina. Methods. This was a retrospective study of 192 E. coli isolates positive for mcr-1 obtained from 69 hospitals of Buenos Aires City and 14 Argentinean provinces in 2012 – 2018. The antimicrobial susceptibility was performed by agar diffusion, broth macrodilution, and/or agar dilution. Standard polymerase chain reaction (PCR) was performed to detect resistance genes and incompatibility groups; specific PCR was applied to discriminate between blaCTX-M allelic groups and mcr-1.5 variant. The genetic relatedness among isolates was evaluated by XbaI-pulsed field gel electrophoresis and multilocus sequence typing in a subset of isolates. Results. All E. coli isolates showed minimal inhibitory concentrations to colistin ≥ 4μg/mL; nearly 50% were resistant to third-generation cephalosporins, with CTX-M-2 being the main extended-spectrum β-lactamase detected. Five E. coli were carbapenemase-producers (3 NDM, 2 KPC). The mcr-1.5 variant was detected in 13.5% of the isolates. No genetic relationship was observed among the mcr-1-positive E. coli clinical isolates, but a high proportion (164/192; 85.4%) of IncI2 plasmids was detected. Conclusions. The presence of IncI2 plasmids among highly diverse E. coli clones suggests that the mcr-1 gene’s wide distribution in Argentina may be driven by the horizontal transmission of IncI2 plasmids.

[RESUMEN]. Objetivo. Describir el perfil de resistencia y las características genéticas de aislamientos clínicos de Escherichia coli que portan el gen movilizable de resistencia a colistina mcr-1 en Argentina. Métodos. Se realizó un estudio retrospectivo para analizar 192 aislamientos de E. coli mcr-1 positivo, obtenidos en 69 hospitales de la Ciudad de Buenos Aires y 14 provincias de Argentina entre 2012 y 2018. La sensibilidad a los antimicrobianos se analizó mediante los métodos de difusión en agar, macrodilución en caldo y/o dilución en agar. Se aplicó la técnica estándar de reacción en cadena de la polimerasa (PCR) para detectar genes de resistencia y grupos de incompatibilidad; se aplicó PCR específica para distinguir entre variantes alélicas del gen blaCTX-M y la variante mcr-1.5. La relación genética entre los aislamientos fue evaluada mediante la técnica de electroforesis en gel de campo pulsado usando la enzima Xbal y la tipificación por secuencias de múltiples locus en un subconjunto de aislamientos. Resultados. Todos los aislamientos de E. coli mostraron concentraciones inhibitorias mínimas de colistina ≥ 4μg/mL. Casi el 50% mostró resistencia a las cefalosporinas de tercera generación y CTX-M-2 fue la β-lactamasa de espectro extendido que más se detectó. Cinco aislamientos de E. coli mostraron ser productoras de carbapenemasas (3 NDM, 2 KPC). La variante mcr-1.5 se detectó en 13,5% de las cepas aisladas. No se observó relación genética entre los aislamientos clínicos estudiados de E. coli positivas para mcr-1, aunque sí se detectó una proporción elevada (164/192; 85,4%) de plásmidos Incl2. Conclusiones. La elevada ocurrencia de plásmidos IncI2 en un grupo altamente diverso de clones de E. coli podría indicar que la amplia difusión del gen mcr-1 en Argentina estaría asociada a la transmisión horizontal de plásmidos IncI2.

[RESUMO]. Objetivo. Descrever o perfil de resistência e as características genéticas de isolados clínicos de Escherichia coli que carregam o gene mobilizábel de resistência à colistina mcr-1 na Argentina. Métodos. Neste estudo retrospectivo, foram analizados 192 isolados de E. coli positivos para mcr-1 obtidos em 69 hospitais da Cidade de Buenos Aires e 14 províncias da Argentina, entre 2012 e 2018. A sensibilidade aos antimicrobianos foi examinada usando métodos de difusão em ágar, macrodiluição em caldo e/ou diluição em ágar. A técnica padrão de reação em cadeia da polimerase (PCR) foi aplicada para detectar genes de resistência e grupos de incompatibilidade; a PCR específica foi aplicada para discriminar entre variantes alélicas do gene blaCTX-M e a variante mcr-1.5. A relação genética entre os isolados foi avaliada por eletroforese em gel de campo pulsado usando a enzima XbaI e a tipagem por sequências de múltiplos lócus, em um subconjunto de isolados. Resultados. Todos os isolados de E. coli apresentaram concentrações inibitórias mínimas de colistina ≥4μg/ mL. Quase 50% foram resistentes às cefalosporinas de terceira geração, e CTX-M-2 foi a β-lactamase de espectro estendido mais detectada. Cinco isolados de E. coli foram produtores de carbapenemase (3 NDM, 2 KPC). A variante mcr-1.5 foi detectada em 13,5% dos isolados. Não foi observada relação genética entre os isolados clínicos de E. coli positivos para mcr-1, mas foi detectada uma alta proporção (164/192; 85,4%) de plasmídeos IncI2. Conclusões. A alta ocorrência de plasmídeos IncI2 em um grupo altamente diverso de clones de E. coli sugere que a ampla distribuição do gene mcr-1 na Argentina estaria associada a transmissão horizontal de plasmídeos IncI2.