[Molecular basis of methicillin-resistance in Staphylococcus aureus]. / Bases moleculares de la resistencia a meticilina en Staphylococcus aureus.

Staphylococcus aureus isolates resistant to several antimicrobials have been gradually emerged since the beginning of the antibiotic era. Consequently, the first isolation of methicillin-resistant S. aureus occurred in 1960, which was described a few years later in Chile. Currently, S. aureus resistant to antistaphylococcal penicillins is endemic in Chilean hospitals and worldwide, being responsible for a high burden of morbidity and mortality. This resistance is mediated by the expression of a new transpeptidase, named PBP2a or PBP2', which possesses lower affinity for the ß-lactam antibiotics, allowing the synthesis of peptidoglycan even in presence of these antimicrobial agents. This new enzyme is encoded by the mecA gene, itself embedded in a chromosomal cassette displaying a genomic island structure, of which there are several types and subtypes. Methicillin resistance is mainly regulated by an induction mechanism activated in the presence of ß-lactams, through a membrane receptor and a repressor of the gene expression. Although mec-independent methicillin resistance mechanisms have been described, they are clearly infrequent.

Bases moleculares de la resistencia a meticilina en Staphylococcus aureus / Molecular basis of methicillin-resistance in Staphylococcus aureus

Resumen Desde el inicio de la era antimicrobiana se han ido seleccionando gradualmente cepas de Staphylococcus aureus resistentes a antimicrobianos de amplio uso clínico. Es así como en 1960 se describen en Inglaterra las primeras cepas resistentes a meticilina, y algunos años después son informadas en hospitales de Chile. Actualmente, S. aureus resistente a penicilinas antiestafilocóccicas es endémico en los hospitales de nuestro país y del mundo, siendo responsable de una alta morbimortalidad. La resistencia es mediada habitualmente por la síntesis de una nueva transpeptidasa, denominada PBP2a o PBP2' que posee menos afinidad por el β-lactámico, y es la que mantiene la síntesis de peptidoglicano en presencia del antimicrobiano. Esta nueva enzima se encuentra codificada en el gen mecA, a su vez inserto en un cassette cromosomal con estructura de isla genómica, de los cuales existen varios tipos y subtipos. La resistencia a meticilina se encuentra regulada, principalmente, por un mecanismo de inducción de la expresión del gen en presencia del β-lactámico, a través de un receptor de membrana y un represor de la expresión. Si bien se han descrito mecanismos generadores de resistencia a meticilina mec independientes, son categóricamente menos frecuentes.

Staphylococcus aureus isolates resistant to several antimicrobials have been gradually emerged since the beginning of the antibiotic era. Consequently, the first isolation of methicillin-resistant S. aureus occurred in 1960, which was described a few years later in Chile. Currently, S. aureus resistant to antistaphylococcal penicillins is endemic in Chilean hospitals and worldwide, being responsible for a high burden of morbidity and mortality. This resistance is mediated by the expression of a new transpeptidase, named PBP2a or PBP2', which possesses lower affinity for the β-lactam antibiotics, allowing the synthesis of peptidoglycan even in presence of these antimicrobial agents. This new enzyme is encoded by the mecA gene, itself embedded in a chromosomal cassette displaying a genomic island structure, of which there are several types and subtypes. Methicillin resistance is mainly regulated by an induction mechanism activated in the presence of β-lactams, through a membrane receptor and a repressor of the gene expression. Although mec-independent methicillin resistance mechanisms have been described, they are clearly infrequent.

Tuberculosis monoarticular de la muñeca: comunicación de un caso / Monoarticular tuberculosis of the wrist: a case report

Resumen La tuberculosis monoarticular aislada de la muñeca es una forma infrecuente de presentación de esta enfermedad, siendo más común el compromiso vertebral. Las formas extravertebrales representan sólo 2 a 3% de las infecciones óseas por Mycobacterium tuberculosis. Presentamos el caso clínico de una mujer de 49 años, con antecedentes de trabajar en labores de aseo en un hospital, que posterior a un trauma de baja energía evolucionó con un cuadro de dolor en la articulación de la muñeca derecha. Diagnosticada inicialmente como una tendinopatía flexora, recibió tratamiento con antiinflamatorios y fisioterapia. Ocho meses después la paciente continuó con dolor a la movilización por lo que se realizó un estudio imagenológico, biopsia y cultivos de tejido óseo. El estudio histopatológico y de biología molecular del tejido confirmó una tuberculosis de muñeca derecha. Se trató con terapia anti-tuberculosa y fisioterapia, consiguiéndose la recuperación funcional de la muñeca.

Monoarticular tuberculosis of the wrist is a rare presentation of primary tuberculosis, being more common skeletal forms involving the spine. Extraspinal tuberculous osteomyelitis is rare and comprises only 2 to 3% of all cases of osteoarticular Mycobacterium tuberculosis infections. We present a case of a 49 years old female patient, who worked as an hospital cleaning employed without other comorbidity. After a low energy injury of the wrist she suffered pain syndrome diagnosticated as a flexor tendinopathy, managed with nonsteroidal antiinflammatory drugs and physical therapy. Eight months later patient evolves with chronic pain in range of motion of right wrist joint, leading to a complete radiological, surgical biopsy and cultures. Histology, and molecular biology confirmed the wrist joint tuberculosis diagnosis. Pharmacological treatment and physical therapy were initiated with appropriated response.

[Monoarticular tuberculosis of the wrist: a case report]. / Tuberculosis monoarticular de la muñeca. Comunicación de un caso.

Monoarticular tuberculosis of the wrist is a rare presentation of primary tuberculosis, being more common skeletal forms involving the spine. Extraspinal tuberculous osteomyelitis is rare and comprises only 2 to 3% of all cases of osteoarticular Mycobacterium tuberculosis infections. We present a case of a 49 years old female patient, who worked as an hospital cleaning employed without other comorbidity. After a low energy injury of the wrist she suffered pain syndrome diagnosticated as a flexor tendinopathy, managed with nonsteroidal antiinflammatory drugs and physical therapy. Eight months later patient evolves with chronic pain in range of motion of right wrist joint, leading to a complete radiological, surgical biopsy and cultures. Histology, and molecular biology confirmed the wrist joint tuberculosis diagnosis. Pharmacological treatment and physical therapy were initiated with appropriated response.

[Colistin in the post-antibiotic era]. / Colistín en la era post-antibiótica.

One of the most important features of the post-antibiotic era in the late 20th century is the resurgence of colistin for the treatment of extensively drug resistant gram-negative bacteria (XDR). Colistin is a narrow spectrum anti-biotic, active against microorganisms with clinical significance such as Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae. Nowadays its toxicity is lower, partly explained by better pharmaceuticals and management of the critically ill patients. However, there has been much confusion regarding the dosage of the drug, its name and labeling, therefore, experts have recommended using a common language about this polymyxin. The lack of PK/PD studies for colistin is perhaps the main weakness of this area of knowledge, even though the before mentioned approach has contributed with new ways to manage and calculate the dose of this antimicrobial. Indeed, the efficiency of colistin in association with a second agent in reducing mortality has not been demonstrated.

Colistín en la era post-antibiótica / Colistin in the post-antibiotic era

One of the most important features of the post-antibiotic era in the late 20th century is the resurgence of colistin for the treatment of extensively drug resistant gram-negative bacteria (XDR). Colistin is a narrow spectrum anti-biotic, active against microorganisms with clinical significance such as Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella pneumoniae. Nowadays its toxicity is lower, partly explained by better pharmaceuticals and management of the critically ill patients. However, there has been much confusion regarding the dosage of the drug, its name and labeling, therefore, experts have recommended using a common language about this polymyxin. The lack of PK/PD studies for colistin is perhaps the main weakness of this area of knowledge, even though the before mentioned approach has contributed with new ways to manage and calculate the dose of this antimicrobial. Indeed, the efficiency of colistin in association with a second agent in reducing mortality has not been demonstrated.

El resurgimiento de colistín para el tratamiento de bacilos gramnegativos extensamente resistentes a antimicrobianos a fines del siglo pasado es una de las características más importantes de la era post-antimicrobiana. Su espectro es reducido y cubre microorganismos con importancia clínica como Acinetobacter baumannii, Pseudomonas aeruginosa y Klebsiella pneumoniae. En contraste a lo que se vio en el pasado, la toxicidad descrita en la actualidad es menor, en parte explicado por las mejores preparaciones farmacéuticas y la optimización del manejo del paciente crítico. Mucha confusión se ha generado respecto a la dosificación del fármaco, debido a la distinta denominación, etiquetado y sugerencias de los laboratorios, a pesar de que el compuesto es el mismo. Por lo anterior, el llamado de los expertos es a utilizar un lenguaje común para referirnos a esta polimixina. Los estudios modernos de PK/PD han contribuido con nuevas formas de administrar y calcular las dosis de este antimicrobiano; no obstante, falta mucho por desarrollar en esta área que se posiciona como su gran debilidad. A pesar que la terapia combinada se sustenta sobre una base teórica lógica, no se ha demostrado que la asociación de colistín con un segundo agente logre disminuir la mortalidad.

[Isolation of Staphylococcus aureus hetero-resistant to vancomycin (hVISA) in the Regional Hospital of Concepción, Chile]. / Aislamiento de Staphylococcus aureus hetero-resistente a vancomicina en Hospital Clínico Regional de Concepción, Chile.

Methicillin-resistant Staphylococcus aureus (MRSA) is widely distributed in hospital environments, causing serious infections, mainly the bloodstream, surgical site infection and pneumonia. Vancomycin (VAN) is the antibiotic of choice for treating severe MRSA infections; however, nowadays worldwide resistant strains (VRSA), with intermediate susceptibility (VISA) and decreased susceptibility or hetero-resistance to VAN (hVISA) have been reported, related to treatment failure and increased mortality. This report describes the first confirmed isolation of MRSA with hVISA phenotype in a public hospital in Chile.

[The pneumococcal connection]. / La conexión neumocóccica.

The resistance of gram-negative bacilli is one of the most important areas in modern medicine, however it hasn't been highlighted the role of the third generation cephalosporins and in particularly ceftriaxone in the selection of gram-negative bacilli resistant to these agents. Paradoxically, ceftriaxone, like the rest of the molecules of this generation, whose initial indication were gram- negative infections began to be used as an agent of choice in pneumococcal infections. The broad spectrum activity of this molecule with its favorable pharmacokinetic properties replaces other agents by this antibiotic in the treatment of a wide range of community acquired infections. However, it wasn't considered the action of this cephalosporin on the microbiome, particularly the intestinal flora, which allowed the selection of enterobacteria that by genetic events, especially parental ß-lactamases mutations (TEM-1, TEM-2, SHV-1), developed resistance to third-generation cephalosporins. The decreased susceptibility to penicillin in Streptococcus pneumoniae isolates that stimulated the growing use of ceftriaxone, was one of the main drivers for the development of resistance to third-generation cephalosporins in gram-negative bacilli.

Actividad de cobre sobre bacilos gramnegativos multi-resistentes aislados en hospitales chilenos / Copper activity against multiresistant Gram negative bacilli isolated from Chilean hospitals

Introduction: Multiresistant nosocomial pathogens, especially Gram-negative bacilli (GNB), are a serious problem for public health systems worldwide. Due to their antimicrobial properties, copper alloys have been suggested as an alternative for the control of bacterial burden in surfaces in hospital environment. However, antibiotic multiresistance and copper resistance could be associated in GNB, and there is evidence that both kind of resistance genes (antibiotic and copper) can be located on the same genetic structures. For this reason antibiotic-multiresistant strains could survive in the presence of copper, selecting for bacterial phenotypes resistant to both antibacterial agents. Aim: To evaluate antibacterial activity of copper against nosocomial extended-spectrum β-lactamases (ESBL) (+) and ESBL (-) GNB, and carbapenems resistant or susceptible strains. Material and Method: This study included 390 strains of GNB isolated from Chilean hospitals: Acinetobacter baumannii and Pseudomonas aeruginosa resistant (CAR R) and susceptible (CAR S) to carbapenem antibiotics, and Klebsiella pneumoniae and Escherichia coli producers and non-producers of ESBL. Susceptibility levels to cupric sulphate were determined by agar dilution method and statistical analysis were used to determine the significance of the differences in the copper tolerance levels between the strains groups. Results: Statistically superior copper tolerance levels were found in the CAR R and ESBL producing strains of A. baumannii and K. pneumoniae, in relation with the CAR S and ESBL not-producing strains. Conclusion: A relation between a diminished susceptibility to ionic copper and to recent generation antimicrobial agents was observed in K. pneumoniae y A. baumannii strains.

Introducción: Los patógenos intrahospitalarios multi-resistentes constituyen un grave problema mundial de salud pública, especialmente los bacilos gramnegativos (BGN). El uso de cobre como antimicrobiano de superficie en hospitales se postula como una alternativa para el control de microorganismos en estos ambientes. Sin embargo, la multi-resistencia a antimicrobianos en BGN hospitalarios puede asociarse con la tolerancia a cobre, ya que existe evidencia que genes que codifican tolerancia a este metal pueden encontrarse en elementos genéticos que confieren resistencia a antimicrobianos. Por esta razón, cepas multi-resistentes a antimicrobianos podrían sobrevivir en presencia de cobre, seleccionando bacterias resistentes a ambos agentes antibacterianos. Objetivo: Investigar la actividad de cobre sobre BGN hospitalarios productores y no productores de β-lactamasas de espectro extendido (BLEE), y resistentes o susceptibles a antimicrobianos carbapenémicos. Material y Métodos: Se estudió 390 cepas de BGN aisladas en hospitales chilenos: Acinetobacter baumannii y Pseudomonas aeruginosa resistentes (CAR R) y susceptibles (CAR S) a carbapenémicos y Klebsiella pneumoniae y Escherichia coli productoras y no productoras de BLEE. Se investigó los niveles de susceptibilidad a sulfato cúprico, mediante dilución seriada en agar y se evaluó la significancia estadística de la diferencia de estos niveles entre los distintos grupos de cepas. Resultados: Se encontraron niveles de tolerancia a cobre superiores en cepas de A. baumannii y K. pneumoniae, CAR R y productoras de BLEE respectivamente, con respecto a sus pares CAR S y no productoras de BLEE. Conclusión: Observamos una relación entre la disminución de la susceptibilidad a cobre iónico y a antimicrobianos de última generación en K. pneumoniae y A. baumannii.

Evolución del consumo de antimicrobianos de uso restringido y tendencia de la susceptibilidad in vitro en el Hospital Regional de Concepción, Chile / Evolution of use of antibiotics of restricted prescription and trend of bacterial susceptibility in Concepcion Regional Hospital, Chile

The aim of this study was analyze the use of restricted antibiotics by patients hospitalized between 2004 and 2008 in Guillermo Grant Benavente Hospital in Concepcion. Also we attempted to identify possible correlations between antibiotic consumption and patterns of bacterial susceptibility. We performed a retrospective observational study that quantified the use of restricted antibiotics using DDD/100-bed-days, and cumulative susceptibility reports informed by the hospital's microbiology laboratory for bacterial susceptibility. The consumption of restricted antibiotics significantly increased between 2004 and 2008 (35%, p = 0.005). The groups with largest use were glycopeptides (37%) and carbapenems (30 %). These results can be explained by the emergence of endemic Methicillin-resistant Staphylococcus aureus (MRSA) and of Extended-spectrum beta-lactamase (ESBL) Gram negative bacilli. Results showed a decrease in susceptibility of P. aeruginosa to imipenem (p = 0.038) and K. pneumoniae to ciprofloxacin (p = 0.021). The total consumption of restricted antibiotic has significantly increased, especially among complex medical services. A significant decrease in bacterial susceptibility has been observed mainly in gram-negative bacilli. The monitoring of antimicrobial prescribing practices and local susceptibility patterns are essential to promote the rational use of antibiotics.

En Chile no existen estudios para cuantificar el consumo de antimicrobianos de uso restringido al interior de los hospitales. Objetivo: Analizar el consumo de antimicrobianos de uso restringido en pacientes hospitalizados durante los años 2004-2008 en el Hospital Guillermo Grant Benavente de Concepción. Además, se analizaron las correlaciones entre este consumo y el patrón de susceptibilidad in vitro. Material y Método: Se diseñó un estudio observacional retrospectivo empleando las DDD/100-días-cama para evaluar el consumo de antimicrobianos, y el informe acumulado de susceptibilidad in vitro entregado por el laboratorio local, para analizar la evolución de la susceptibilidad. Resultados: El consumo de antimicrobianos se incrementó en 35% (p = 0,005) durante los años 2004-2008, donde los más consumidos fueron glicopéptidos (37%) y carbapenémicos (30%). Estos resultados se pueden explicar por la aparición de cepas de Staphylococcus aureus resistente a meticilina y bacilos gramnegativos productores de Q-lactamasas de espectro extendido. Además, se observó una disminución de la susceptibilidad de Pseudomonas aeruginosa a imipenem (p = 0,038) y de Klebsiella pneumoniae a ciprofloxacina (p = 0,021). Conclusiones: El consumo total de antimicrobianos de uso restringido se incrementó significativamente en los servicios clínicos más complejos, observándose una disminución de la susceptibilidad de algunos bacilos gramnegativos. El monitoreo de la prescripción de antimicrobianos así como de la susceptibilidad in vitro local constituyen medidas esenciales para promover el uso racional de antimicrobianos.

[Evolution of use of antibiotics of restricted prescription and trend of bacterial susceptibility in Concepcion Regional Hospital, Chile]. / Evolución del consumo de antimicrobianos de uso restringido y tendencia de la susceptibilidad in vitro en el Hospital Regional de Concepción, Chile.

The aim of this study was analyze the use of restricted antibiotics by patients hospitalized between 2004 and 2008 in Guillermo Grant Benavente Hospital in Concepcion. Also we attempted to identify possible correlations between antibiotic consumption and patterns of bacterial susceptibility. We performed a retrospective observational study that quantified the use of restricted antibiotics using DDD/100-bed-days, and cumulative susceptibility reports informed by the hospital's microbiology laboratory for bacterial susceptibility. The consumption of restricted antibiotics significantly increased between 2004 and 2008 (35%, p = 0.005). The groups with largest use were glycopeptides (37%) and carbapenems (30 %). These results can be explained by the emergence of endemic Methicillin-resistant Staphylococcus aureus (MRSA) and of Extended-spectrum beta-lactamase (ESBL) Gram negative bacilli. Results showed a decrease in susceptibility of P. aeruginosa to imipenem (p = 0.038) and K. pneumoniae to ciprofloxacin (p = 0.021). The total consumption of restricted antibiotic has significantly increased, especially among complex medical services. A significant decrease in bacterial susceptibility has been observed mainly in gram-negative bacilli. The monitoring of antimicrobial prescribing practices and local susceptibility patterns are essential to promote the rational use of antibiotics.

[Copper activity against multiresistant Gram negative bacilli isolated from Chilean hospitals]. / Actividad de cobre sobre bacilos gramnegativos multi-resistentes aislados en hospitales chilenos.

INTRODUCTION: Multiresistant nosocomial pathogens, especially Gram-negative bacilli (GNB), are a serious problem for public health systems worldwide. Due to their antimicrobial properties, copper alloys have been suggested as an alternative for the control of bacterial burden in surfaces in hospital environment. However, antibiotic multiresistance and copper resistance could be associated in GNB, and there is evidence that both kind of resistance genes (antibiotic and copper) can be located on the same genetic structures. For this reason antibiotic-multiresistant strains could survive in the presence of copper, selecting for bacterial phenotypes resistant to both antibacterial agents. AIM: To evaluate antibacterial activity of copper against nosocomial extended-spectrum ß-lactamases (ESBL) (+) and ESBL (-) GNB, and carbapenems resistant or susceptible strains. MATERIAL AND METHOD: This study included 390 strains of GNB isolated from Chilean hospitals: Acinetobacter baumannii and Pseudomonas aeruginosa resistant (CAR R) and susceptible (CAR S) to carbapenem antibiotics, and Klebsiella pneumoniae and Escherichia coli producers and non-producers of ESBL. Susceptibility levels to cupric sulphate were determined by agar dilution method and statistical analysis were used to determine the significance of the differences in the copper tolerance levels between the strains groups. RESULTS: Statistically superior copper tolerance levels were found in the CAR R and ESBL producing strains of A. baumannii and K. pneumoniae, in relation with the CAR S and ESBL not-producing strains. CONCLUSION: A relation between a diminished susceptibility to ionic copper and to recent generation antimicrobial agents was observed in K. pneumoniae y A. baumannii strains.

[Multi-drug efflux pumps and antibiotic resistance in Acinetobacter baumannii]. / Bombas de expulsión multidrogas en Acinetobacter baumannii y resistencia a antimicrobianos.

Bacterial multi-drugs systems contribute to the development of multi-resistance patterns of Acinetobacter baumannii, a nosocomial pathogen of increasing importance due to its emerging resistance to carbapenems. The multi-resistance phenomena is generated by a combination of mechanisms, one of which the efflux pump system. Many of these multiresistant isolates of A. baumannii harbor genes for the AdeABC multi-drug efflux system, related with resistance to various groups of antibacterial agents, including tygecicline and meropenem. Inhibition of these systems would allow to increase the efficacy of this antimicrobial. This review focuses on the multi-drug efflux pump system of A. baumannii with special emphasis in the AdeABC system.

[Molecular identification of aminoglycoside-modifying enzymes among strains of Enterococcus spp. isolated in hospitals of the VIII Region of Chile]. / Identificación molecular de enzimas modificantes de aminoglucósidos en cepas de Enterococcus spp. aisladas en hospitales de la Octava Región de Chile.

BACKGROUND: Infectious diseases produced by Enterococcus spp, must be treated with a synergistic combination between a penicillin and an aminoglycoside. High level resistance to aminoglycosides is a serious therapeutic problem, since it predicts the loss of synergistic activity of this antimicrobial combination. AIM: To investigate the presence of genes encoding aminoglycoside-modifying enzymes (AMEs) among strains of Enterococcus spp with high level of resistance to aminoglycosides. MATERIAL AND METHODS: The genes encoding some of the AMEs were investigated among 305 aminoglycoside-resistant strains of Enterococcus spp isolated in hospitals of the VIII region of Chile, by dot blot hybridization and Polymerase Chain Reaction (PCS). RESULTS: High level resistance to some aminoglycosides was observed in 104 strains (34.1 %) and 93 of these harbored at least one of the genes encoding the investigated AMEs. Three genes were detected: aac(6)Ie-aph(2")Ia (14.8%) encoding for the enzyme AAC(6)Ie-APH(2")Ia (resistance to all aminoglycosides, except streptomycin); aph(3)IIIa (26%), and ant(6)la (28.5%) encoding for the phosphorylating enzymes APH(3)Ilia (resistance to kanamycin, amikacin and neomycin), and ANT(6)-la (resistance only to streptomycin), respectively. None of the strains harbored the gene ant (4) which encode for the enzyme ANT (4). CONCLUSION: The low frequency of strains harbouring the bifunctional enzyme (<15%), conferring an extended resistance profile to aminoglycosides, allows us to propose the empirical use of aminoglycoside-aminocyclitols, associated to a penicillin, in the treatment of serious infections produced by species of enterococci.

[Integrons and resistance gene cassettes: structure and role against antimicrobials]. / Integrones y cassettes genéticos de resistencia: estructura y rol frente a los antibacterianos.

Bacteria have developed sophisticated and successful genetic mechanisms to evade the action of antimicrobials. Bacterial multiresistance has caused serious problems in the treatment of nosocomial infections. Integrons and gene cassettes are considered the main genetic elements in the evolution of plasmids and transposons that actively participate in the mobilization of genes, codifying different bacterial resistance mechanisms. This article reviews the historical and structural aspects of integrons and resistance gene cassettes and the presence of these structures in gram negative bacteria isolated from Chilean hospitals in the last ten years.

[Resistance to gentamicin, amikacin and ciprofloxacin among nosocomial isolates of klebsiella pneumoniae subspecie pneumoniae producing extended spectrum beta-lactamases]. / Resistencia a gentamicina, amikacina y ciprofloxacina en cepas hospitalarias de klebsiella pneumoniae subespecie pneumoniae productoras de beta-lactamasas de espectro extendido.

BACKGROUND: Klebsiella pneumoniae is a pathogenic bacterium frequently isolated from nosocomial samples, specially the subspecie pneunonlae, with extensive antibiolic resistance profiles, including third generation cepbhalosporiis, aminoglycosides and quinolones. This is specially true for those strains producing extended spectrum beta lactamases (ESBL). AIM: To investigate the susceptibility to gentamicin, amikacin and ciprofloxacin and the presence of some aminogloycoside modifying enzyme (AMEs) among nosocomial strains of K pneumoniae subspecie pneumoniae producing ESBL. MATERIAL AND METHODS: The antibiotic resistant patterns and the level of resistance (minimal inhibitory concentration, MIC) of 100 strains, isoklted from sel ,eal bospitals of dcifferent Chilean cities, were deterl,in,ed. Tbe presence of some aminoglycosides modifying enzyme (AMEs) was investigated by PCR. RESULTS: Sixty five percent of strains were resistant to gentamicin, 47% were resistant to amikacin, and 29% were resistant to ciprofloxacin. The most frequent AMEs genes detected were the aac(6')-Ib gene (6'N-Acetyltransferase type Ib enzyme) in 69% of strains, conferring resistance to amikacin, kanamycin, tobramycin, and nieoniycin, and the gene aac(3)-IIa (3-Acetyltransferase type 3-IIa enzyme), in 36% of strains, conferring resistance to gentamlicin. CONCLUSIONS: Among nosocomial strains of K pneumoniae subspecie pneumoniae isolaterd from Chilean hospitals, there is an association between the production of ESBL and the resistance to others antimicrobial agents, especially aminoglycosides. Nevertheless, 71% of isolates are susceptible to ciprofloxacin.