Chromosome-Mediated Colistin Resistance in Clinical Isolates of Klebsiella pneumoniae and Escherichia coli: Mutation Analysis in the Light of Genetic Background.

Purpose: Colistin resistance mechanisms involving mutations in chromosomal genes associated with LPS modification are not completely understood. Mutations in genes coding for the MgrB regulator frequently account for colistin resistance in Klebsiella pneumoniae, whereas mutations in genes coding for PhoPQ and PmrAB are frequent in E. coli. Our aim was to perform a genetic analysis of chromosomal mutations in colistin-resistant (MIC ≥4 µg/mL) clinical isolates of K. pneumoniae (n = 8) and E. coli (n = 7) of different STs. Methods: Isolates were obtained in a 3-year period in a university hospital in Santiago, Chile. Susceptibility to colistin, aminoglycosides, cephalosporins, carbapenems and ciprofloxacin was determined through broth microdilution. Whole genome sequencing was performed for all isolates and chromosomal gene sequences were compared with sequences of colistin-susceptible isolates of the same sequence types. Results: None of the isolates carried mcr genes. Most of the isolates were susceptible to all the antibiotics analyzed. E. coli isolates were ST69, ST127, ST59, ST131 and ST14, and K. pneumoniae isolates were ST454, ST45, ST6293, ST380 and ST25. All the isolates had mutations in chromosomal genes analyzed. K. pneumoniae had mutations mainly in mgrB gene, whereas E. coli had mutations in pmrA, pmrB and pmrE genes. Most of the amino acid changes in LPS-modifying enzymes of colistin-resistant isolates were found in colistin-susceptible isolates of the same and/or different ST. Eleven of them were found only in colistin-resistant isolates. Conclusion: Colistin resistance mechanisms depend on genetic background, and are due to chromosomal mutations, which implies a lower risk of transmission than plasmid-mediated genes. Colistin resistance is not associated with multidrug-resistance, nor to high-risk sequence types.

Campylobacter spp. Prevalence in Santiago, Chile: A Study Based on Molecular Detection in Clinical Stool Samples from 2014 to 2019.

Campylobacter spp. is an emerging cause of infectious diarrhea worldwide. In South American countries such as Chile, its prevalence is underestimated due to inadequate detection methods. Gastrointestinal multiplex PCR panels (GMP) permit rapid and sensitive detection of bacterial pathogens and provide important epidemiological information. This study aimed to analyze Campylobacter epidemiology using the results of molecular methods and to compare molecular detection results to those of culture methods. We performed a retrospective, descriptive analysis of Campylobacter spp. detected in clinical stool samples between 2014-2019 by GMP and culture. Within 16,582 specimens examined by GMP, Campylobacter was the most prevalent enteropathogenic bacteria (8.5%), followed by Salmonella spp. (3.9%), Shigella spp./enteroinvasive Escherichia coli (EIEC) (1.9%), and Yersinia enterocolitica (0.8%). The highest Campylobacter prevalence occurred in 2014/2015. Campylobacteriosis affected more males (57.2%) and adults from 19-65 years (47.9%) and showed a bimodal seasonality with summer and winter peaks. In 11,251 routine stool cultures, Campylobacter spp. was detected in 4.6%, mostly C. jejuni (89.6%). Among 4533 samples tested by GMP and culture in parallel, GMP showed a superior sensitivity (99.1% versus 50%, respectively). The study suggests that Campylobacter spp. is the most frequent bacterial enteropathogen in Chile.

Longitudinal assessment of SARS-CoV-2 IgG seroconversionamong front-line healthcare workers during the first wave of the Covid-19 pandemic at a tertiary-care hospital in Chile.

BACKGROUND: Healthcare workers (HCWs) are at high risk of exposure to SARS-CoV-2. Cross-sectional studies have provided variable rates of seroprevalence in HCWs. Longitudinal assessments of the serological response to Covid-19 among HCWs are crucial to understanding the risk of infection and changes in antibody titers over time. We aimed to investigate seroprevalence and risk factors associated with seroconversion in a prospective cohort of HCWs during the peak of the first wave of the Covid-19 pandemic. METHODS: We conducted a longitudinal study among 446 front-line HCWsin a tertiary-care hospital in Chile from April to July 2020. IgG was determined monthly using two different ELISAs in serum samples of HCWs, during the three-month period. In each visit, demographic data, symptoms, risk factors, and exposure risks were also assessed. RESULTS: The overall seroprevalence at the end of the study period was 24% (95% CI20.2-28.3), with 43% of seropositive HCWs reporting no prior symptoms. Seroconversion rates significantly differed over the study period, from 2.1% to as high as 8.8% at the peak of the epidemic. There were no statistically significant differences observed between HCWs in direct clinical care of patients with Covid-19 and those working in low risk areas. Antibody titers appeared to wane over time. CONCLUSIONS: HCWs were severely affected with a high rate of seroconversion that appeared to mirror the local epidemiological situation. A significant amount of participants underwent an asymptomatic infection, highlighting the need for improved surveillance policies. Antibody titers appear to wane over time; further studies to understand this finding's impact on the risk of reinfection are warranted.

Evaluation of two fluorescence immunoassays for the rapid detection of SARS-CoV-2 antigen-new tool to detect infective COVID-19 patients.

BACKGROUND: Real-Time Reverse-Transcription Polymerase Chain Reaction (RT-PCR) is currently the only recommended diagnostic method for SARS-CoV-2. However, rapid immunoassays for SARS-CoV-2 antigen could significantly reduce the COVID-19 burden currently weighing on laboratories around the world. METHODS: We evaluated the performance of two rapid fluorescence immunoassays (FIAs), SOFIA SARS Antigen FIA (Quidel Corporation, San Diego, CA, USA) and STANDARD F COVID-19 Ag FIA (SD Biosensor Inc., Gyeonggi-do, Republic of Korea), which use an automated reader. The study used 64 RT-PCR characterized clinical samples (32 positive; 32 negative), which consisted of nasopharyngeal swabs in universal transport medium. RESULTS: Of the 32 positive specimens, all from patients within 5 days of symptom onset, the Quidel and SD Biosensor assays detected 30 (93.8%) and 29 (90.6%) samples, respectively. Among the 27 samples with high viral loads (Ct ≤ 25), the two tests had a sensitivity of 100%. Specificity was 96.9% for both kits. CONCLUSION: The high performance of the evaluated FIAs indicates a potential use as rapid and PCR-independent tools for COVID-19 diagnosis in early stages of infection. The excellent sensitivity to detect cases with viral loads above ~106 copies/mL (Ct values ≤ 25), the estimated threshold of contagiousness, suggests that the assays might serve to rapidly identify infective individuals.

[Identification of mycobacteria species through mass spectrometry (MALDI-TOF)]. / Identificación de especies de micobacterias mediante espectrometría de masas (MALDI-TOF).

BACKGROUND: Mycobacterial diseases are very important both clinically and epidemiologically. Mycobacterium tuberculosis complex (MTBc) infections confer higher morbidity and mortality rate than non-tuberculous mycobacteria (NTM) infections. Traditional species identification techniques are based on phenotypic characteristics which take a long time by laborious processes and in occasions are no conclusive. Currently, most used techniques are based on molecular methods, which are accurate but are expensive and complex. Matrix Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF MS) is a simple, cheap and fast identification method based on comparing protein spectra with a reference database. AIM: To assess the performance of MALDI-TOF MS in the identification of MTBc and NTM, compared with molecular methods. METHODS: For that purpose, 28 isolates of 9 different species were analyzed through MALDI-TOF MS. RESULTS: 78.5% (22/28) of isolates were correctly identified, 100% (9/9) of rapidly growers NTM, 60% (9/15) of slow growing NTM and 100% (4/4) of MTBc. Every unidentified isolate (6/6) corresponded to M. avium/intracellulare complex. CONCLUSION: MALDI-TOF MS is fast, simple and cheaper than molecular methods and also has adequate accuracy.

[Nocardia cyriacigeorgica infection in AIDS patient]. / Infección por Nocardia cyriacigeorgica en paciente con infección por VIH en etapa SIDA.

Nocardiosis is a localized or systemic infection that mainly affects immunocompromised patients, with pulmonary localization being the most frequent site. The transmission comes mainly from the inhalation of spores or by direct inoculation into the skin and ocular mucosa. More than 90 species of nocardia are described, of which more than half are recognized as pathogens in humans. The best known species of medical importance are Nocardia farcinica, Nocardia abscessus, Nocardia nova y Nocardia brasiliensis. In Chile, there have been published cases of Nocardia asteroides and Nocardia farcinica infections. Nocardia cyriacigeorgica is considered an emerging species, there being no cases previously described in our country. We present a clinical case of pulmonary nocardiosis in an acquired immunodeficiency syndrome (AIDS) patient.

Evaluation of a novel antigen-based rapid detection test for the diagnosis of SARS-CoV-2 in respiratory samples.

OBJECTIVES: In the context of the coronavirus disease 2019 (COVID-19) pandemic, the development and validation of rapid and easy-to-perform diagnostic methods are of high priority. This study was performed to evaluate a novel rapid antigen detection test (RDT) for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in respiratory samples. METHODS: The fluorescence immunochromatographic SARS-CoV-2 antigen test (Bioeasy Biotechnology Co., Shenzhen, China) was evaluated using universal transport medium with nasopharyngeal (NP) and oropharyngeal (OP) swabs from suspected COVID-19 cases. Diagnostic accuracy was determined in comparison to SARS-CoV-2 real-time (RT)-PCR. RESULTS: A total of 127 samples were included; 82 were RT-PCR-positive. The median patient age was 38 years, 53.5% were male, and 93.7% were from the first week after symptom onset. Overall sensitivity and specificity were 93.9% (95% confidence interval 86.5-97.4%) and 100% (95% confidence interval 92.1-100%), respectively, with a diagnostic accuracy of 96.1% and Kappa coefficient of 0.9. Sensitivity was significantly higher in samples with high viral loads. CONCLUSIONS: The RDT evaluated in this study showed a high sensitivity and specificity in samples mainly obtained during the first week of symptoms and with high viral loads, despite the use of a non-validated sample material. The assay has the potential to become an important tool for early diagnosis of SARS-CoV-2, particularly in situations with limited access to molecular methods.

Identificación de especies de micobacterias mediante espectrometría de masas (MALDI-TOF) / Identification of mycobacteria species through mass spectrometry (MALDI-TOF)

Resumen Introducción: Las enfermedades producidas por micobacterias son de gran importancia clínica y epidemiológica presentando el complejo Mycobacterium tuberculosis (MTBc) una morbi-mortalidad mayor que la producida por micobacterias no tuberculosas (MNTB). La identificación tradicional está basada en sus características fenotípicas mediante procesos laboriosos e incapaces en algunos casos de distinguir entre especies. Actualmente, la mayoría de las técnicas utilizadas se basan en métodos moleculares que tienen alta veracidad, pero son complejas y de alto costo. La espectrometría de masas con desorción/ionización láser asistida por una matriz asociada a tiempo de vuelo (MALDI-TOF MS) se basa en la comparación del espectro proteico producido con respecto al de una base de datos de referencia. Objetivo: Evaluar el rendimiento de MALDI-TOF MS en la identificación de micobacterias comparado con métodos moleculares: Material y Métodos: Se analizaron 28 aislados de nueve especies distintas mediante MALDI-TOF MS. Resultados: Se identificó correctamente 78,5% de las aislados (22/28), concordante en 100% (9/9) de MNTB de crecimiento rápido, 60% (9/15) en las MNTB de crecimiento lento y 100% (4/4) de MTBc. Todas las especies no identificadas (6/6) pertenecen al complejo M. avium/intracellulare. Conclusión: MALDI-TOD MS es una metodología rápida, fácil y de bajo costo, con adecuada veracidad respecto a los métodos moleculares.

Abstract Background: Mycobacterial diseases are very important both clinically and epidemiologically. Mycobacterium tuberculosis complex (MTBc) infections confer higher morbidity and mortality rate than non-tuberculous mycobacteria (NTM) infections. Traditional species identification techniques are based on phenotypic characteristics which take a long time by laborious processes and in occasions are no conclusive. Currently, most used techniques are based on molecular methods, which are accurate but are expensive and complex. Matrix Assisted Laser Desorption/Ionization Time-of-Flight mass spectrometry (MALDI-TOF MS) is a simple, cheap and fast identification method based on comparing protein spectra with a reference database. Aim: To assess the performance of MALDI-TOF MS in the identification of MTBc and NTM, compared with molecular methods. Methods: For that purpose, 28 isolates of 9 different species were analyzed through MALDI-TOF MS. Results: 78.5% (22/28) of isolates were correctly identified, 100% (9/9) of rapidly growers NTM, 60% (9/15) of slow growing NTM and 100% (4/4) of MTBc. Every unidentified isolate (6/6) corresponded to M. avium/intracellulare complex. Conclusion: MALDI-TOF MS is fast, simple and cheaper than molecular methods and also has adequate accuracy.

Infección por Nocardia cyriacigeorgica en paciente con infección por VIH en etapa SIDA / Nocardia cyriacigeorgica infection in AIDS patient

Resumen La nocardiosis es una infección localizada o sistémica que afecta principalmente a pacientes inmunocomprometidos, siendo la localización pulmonar el sitio más frecuente. La transmisión proviene principalmente de la inhalación de esporas o mediante la inoculación directa en la piel y mucosa ocular. Se han descrito más de 90 especies de Nocardia, de éstas más de la mitad son reconocidas como patógenos en humanos. Las especies de importancia médica más conocidas son Nocardia farcinica, Nocardia abscessus, Nocardia nova y Nocardia brasiliensis. En Chile hay casos publicados de infección por Nocardia asteroides y N. farcinica. Nocardia cyriacigeorgica se considera una especie emergente, no habiendo casos descritos previamente en nuestro país. Presentamos el caso clínico de una nocardiosis pulmonar en un paciente con síndrome de inmunodeficiencia adquirida (SIDA).

Abstract Nocardiosis is a localized or systemic infection that mainly affects immunocompromised patients, with pulmonary localization being the most frequent site. The transmission comes mainly from the inhalation of spores or by direct inoculation into the skin and ocular mucosa. More than 90 species of nocardia are described, of which more than half are recognized as pathogens in humans. The best known species of medical importance are Nocardia farcinica, Nocardia abscessus, Nocardia nova y Nocardia brasiliensis. In Chile, there have been published cases of Nocardia asteroides and Nocardia farcinica infections. Nocardia cyriacigeorgica is considered an emerging species, there being no cases previously described in our country. We present a clinical case of pulmonary nocardiosis in an acquired immunodeficiency syndrome (AIDS) patient.

Epidemiología de la enfermedad fúngica invasora por hongos filamentosos en el período 2005 a 2015, en un hospital universitario en Santiago, Chile / Epidemiology of invasive fungal disease by filamentous fungi in the period 2005 to 2015, in a university hospital in Santiago, Chile

Resumen Introducción: La enfermedad fúngica invasora (EFI) por hongos filamentosos es cada vez más frecuente. Objetivo: Estudiar la epidemiología de la EFI en adultos hospitalizados en nuestro centro. Metodología: Estudio retrospectivo de pacientes adultos de un hospital universitario en Santiago, Chile, con EFI por hongos filamentosos entre enero de 2005 y diciembre de 2015. Resultados: Se identificaron 125 episodios, siendo 48% categoria probada, 40% probable y 11% posible según criterios EORTC/MSG, incidencia global 0,47 x 1.000 egresos, 57% pacientes masculinos y edad de 50 ± 16 años. El 66,4% tenía patología hematológica, 11,2% trasplante de órgano sólido, 11,2% enfermedad reumatológica, 11,2% otra condición. Los factores de riesgo fueron neutropenia 44%, corticoterapia 21%, inmunosupresores 13%. Los hongos más frecuentemente identificados fueron Aspergillus spp (53,6%), Mucorales (16%), Fusarium spp (8,8%), Alternaria spp (5,6%), otros filamentosos (3,2%). Todos recibieron antifúngicos, 82% monoterapia, 18% terapia combinada, hubo defocación quirúrgica en 90% de mucormicosis. La mortalidad global fue 42%. Al comparar 2005-2009 vs 2010-2015, hubo un aumento significativo de la incidencia y una tendencia a menor mortalidad en el segundo período. Conclusiones: Durante un período de 10 años, observamos un aumento de la incidencia de EFI por filamentosos, aspergilosis fue la etiología más frecuente y la mortalidad global fue 42%.

Background: Invasive fungal disease (IFD) due to filamentous fungi is increasingly common. Aim: To study the epidemiology of EFI in hospitalized adults in our center. Methods: Retrospective study of adult patients of a university hospital in Santiago, Chile, with EFI due to filamentous fungi between January 2005 and December 2015. Results: 125 episodes were identified, being 48% proven, 40% probable and 11% possible according to EORTC/MSG criteria, overall incidence was 0.47/1,000 admissions, 57% male patients and age 50 ± 16 years. 66.4% had hematological pathology, 11.2% solid organ transplant, 11.2% rheumatology diseases, 11.2% other conditions. The risk factors were neutropenia 44%, corticosteroid therapy 21%, immunosuppressants 13%. The most frequent mould identified were Aspergillus spp (53.6%), Mucorales (16%), Fusarium spp (8.8%), Alternaria spp (5.6%) and other filamentous (3.2%). All received antifungals, 82% monotherapy, 18% combined therapy, there was surgical defocation in 90% of mucormycosis. The overall mortality was 42%. When comparing 2005-2009 vs 2010-2015, there was a significant increase in incidence and a tendency to lower mortality in the second period. Conclusions: Over a period of 10 years, we observed an increase in the incidence of EFI by filamentous, aspergillosis was the most frequent etiology and the overall mortality was 42%.

Evaluation of a rapid immunochromatographic test for detection of KPC in clinical isolates of Enterobacteriaceae and Pseudomonas species.

The KPC K-SeT immunochromatographic test (Coris BioConcept®, Gembloux, Belgium) has been widely used for detection of KPC in Enterobacteriaceae with reported sensitivities and specificities of 100%. However, to our knowledge, there are no reports of its use in KPC-positive Pseudomonas species. We evaluated the KPC K-SeT test in 36 clinical isolates of Enterobacteriaceae (21 KPC-positive and 15 KPC-negative) and 20 Pseudomonas species (5 KPC-positive and 15 KPC-negative) using conventional PCR for carbapenemase genes as the reference method. The KPC K-SeT test detected 25 out of 26 KPC-positive isolates (96.1%). The undetected isolate was 1 P. aeruginosa bearing the mutation D179Y in the omega loop region of KPC-2 carbapenemase. This mutation was already reported in Enterobacteriaceae as conferring resistance to ceftazidime-avibactam. To our knowledge, this is the first report of evaluation of KPC K-SeT test in KPC-positive P. aeruginosa isolates.

Genetic analysis of the first mcr-1 positive Escherichia coli isolate collected from an outpatient in Chile.

Global dissemination of mcr-like genes represents a serious threat to public health since it jeopardizes the effectiveness of colistin, an antibiotic used as a last-resort treatment against highly antibiotic-resistant bacteria. In 2017, a mcr-1-positive isolate of Escherichia coli was found in Chile for the first time. Herein we report the genetic features of this strain (UCO-457) by whole-genome sequencing (WGS) and conjugation experiments. The UCO-457 strain belonged to ST4204 and carried a 285 kb IncI2-type plasmid containing the mcr-1 gene. Moreover, this plasmid was transferred by conjugation to an E. coli J53 strain at high frequency. The isolate harbored the cma, iroN, and iss virulence genes and did carry resistance genes to trimethoprim/sulfamethoxazole and fluoroquinolones. Other antibiotic resistance determinants such as ß-lactamases-encoding genes were not detected, making the isolate highly susceptible to these antibiotics. Our results revealed that such susceptible isolates could be acting as platforms to disseminate plasmid-mediated colistin resistance. Based on this evidence, we consider that mcr-like prevalence deserves urgent attention and should be examined not only in highly resistant bacteria but also in susceptible isolates.

Genetic analysis of the first mcr-1 positive Escherichia coli isolate collected from an outpatient in Chile

ABSTRACT Global dissemination of mcr-like genes represents a serious threat to public health since it jeopardizes the effectiveness of colistin, an antibiotic used as a last-resort treatment against highly antibiotic-resistant bacteria. In 2017, a mcr-1-positive isolate of Escherichia coli was found in Chile for the first time. Herein we report the genetic features of this strain (UCO-457) by whole-genome sequencing (WGS) and conjugation experiments. The UCO-457 strain belonged to ST4204 and carried a 285 kb IncI2-type plasmid containing the mcr-1 gene. Moreover, this plasmid was transferred by conjugation to an E. coli J53 strain at high frequency. The isolate harbored the cma, iroN, and iss virulence genes and did carry resistance genes to trimethoprim/sulfamethoxazole and fluoroquinolones. Other antibiotic resistance determinants such as β-lactamases-encoding genes were not detected, making the isolate highly susceptible to these antibiotics. Our results revealed that such susceptible isolates could be acting as platforms to disseminate plasmid-mediated colistin resistance. Based on this evidence, we consider that mcr-like prevalence deserves urgent attention and should be examined not only in highly resistant bacteria but also in susceptible isolates.

A prospective, multi-center study of Candida bloodstream infections in Chile.

BACKGROUND: Active surveillance is necessary for improving the management and outcome of patients with candidemia. The aim of this study was to describe epidemiologic and clinical features of candidemia in children and adults in tertiary level hospitals in Chile. METHODS: We conducted a prospective, multicenter, laboratory-based survey study of candidemia in 26 tertiary care hospitals in Chile, from January 2013 to October 2017. RESULTS: A total of 780 episodes of candidemia were included, with a median incidence of 0.47/1,000 admissions. Demographic, clinical and microbiological information of 384 cases of candidemia, from 18 hospitals (7,416 beds), was included in this report. One hundred and thirty-four episodes (35%) occurred in pediatric patients and 250 (65%) in adult population. Candida albicans (39%), Candida parapsilosis (30%) and Candida glabrata (10%) were the leading species, with a significant difference in the distribution of species between ages. The use of central venous catheter and antibiotics were the most frequent risk factors in all age groups (> 70%). Three hundred and fifteen strains were studied for antifungal susceptibility; 21 strains (6.6%) were resistant to fluconazole, itraconazole, voriconazole, anidulafungin or micafungin. The most commonly used antifungal therapies were fluconazole (39%) and echinocandins (36%). The overall 30-day survival was 74.2%, significantly higher in infants (82%) and children (86%) compared with neonates (72%), adults (71%) and elderly (70%). CONCLUSIONS: Our prospective, multicenter surveillance study showed a low incidence of candidemia in Chile, with high 30-day survival, a large proportion of elderly patients, C. glabrata as the third most commonly identified strain, a 6.6% resistance to antifungal agents and a frequent use of echinocandins.

[Epidemiology of invasive fungal disease by filamentous fungi in the period 2005 to 2015, in a university hospital in Santiago, Chile]. / Epidemiología de la enfermedad fúngica invasora por hongos filamentosos en el período 2005 a 2015, en un hospital universitario en Santiago, Chile.

BACKGROUND: Invasive fungal disease (IFD) due to filamentous fungi is increasingly common. AIM: To study the epidemiology of EFI in hospitalized adults in our center. METHODS: Retrospective study of adult patients of a university hospital in Santiago, Chile, with EFI due to filamentous fungi between January 2005 and December 2015. RESULTS: 125 episodes were identified, being 48% proven, 40% probable and 11% possible according to EORTC/MSG criteria, overall incidence was 0.47/1,000 admissions, 57% male patients and age 50 ± 16 years. 66.4% had hematological pathology, 11.2% solid organ transplant, 11.2% rheumatology diseases, 11.2% other conditions. The risk factors were neutropenia 44%, corticosteroid therapy 21%, immunosuppressants 13%. The most frequent mould identified were Aspergillus spp (53.6%), Mucorales (16%), Fusarium spp (8.8%), Alternaria spp (5.6%) and other filamentous (3.2%). All received antifungals, 82% monotherapy, 18% combined therapy, there was surgical defocation in 90% of mucormycosis. The overall mortality was 42%. When comparing 2005-2009 vs 2010-2015, there was a significant increase in incidence and a tendency to lower mortality in the second period. CONCLUSIONS: Over a period of 10 years, we observed an increase in the incidence of EFI by filamentous, aspergillosis was the most frequent etiology and the overall mortality was 42%.

[First report in Chile of a clinical isolate of Escherichia coli resistant to colistin harbouring the mcr-1 gene]. / Primera comunicación en Chile de la detección del gen mcr-1 en un aislado clínico de Escherichia coli resistente a colistín.

Recently it was described the plasmidial gene mcr-1 associated with colistin resistance. We screened by PCR and sequencing for gene mcr-1 in thirteen clinical isolates resistant to colistin. We observed amplification in one E. coli. To our knowledge, this is the first report of the presence of mcr-1 gene in Chile.