Figura 4 - uploaded by Gerardo González-Rocha
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Mecanismo de acción de las polimixinas. A: Inicialmente se genera una atracción electrostática entre la polimixina, de carga neta positiva, y el lípido A, de carga negativa, lo que genera el desplazamiento repulsivo de los cationes divalentes que estabilizan el LPS, a lo que sigue la inserción del antimicrobiano a través de sus residuos hidrófobos en la membrana externa; B: Una vez inserta la polimixina, se genera una alteración estructural de la membrana citoplasmática que llevaría a la lisis bacteriana por pérdida de la resistencia osmótica. LPS: lipopolisacárido; G: glucosamina; P: fosfato; Mg 2+ : ion magnesio; Ca 2+ : ion calcio. Intencionalmente no se esquematizó el core ni el antígeno O.  

Mecanismo de acción de las polimixinas. A: Inicialmente se genera una atracción electrostática entre la polimixina, de carga neta positiva, y el lípido A, de carga negativa, lo que genera el desplazamiento repulsivo de los cationes divalentes que estabilizan el LPS, a lo que sigue la inserción del antimicrobiano a través de sus residuos hidrófobos en la membrana externa; B: Una vez inserta la polimixina, se genera una alteración estructural de la membrana citoplasmática que llevaría a la lisis bacteriana por pérdida de la resistencia osmótica. LPS: lipopolisacárido; G: glucosamina; P: fosfato; Mg 2+ : ion magnesio; Ca 2+ : ion calcio. Intencionalmente no se esquematizó el core ni el antígeno O.  

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... En nuestro país, el cambio de siglo -en el mundo desarrollado décadas antes-trajo la descripción creciente de infecciones producidas por bacilos gramnegativos extremadamente resistentes a antimicrobianos, existiendo incluso controversia sobre cómo denominar a estos aislados (Tabla 1). Es en este contexto donde la falta de nuevos antimicrobianos motivó la reutilización de un agente prácticamente olvidado 39 . ...
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... Actualmente existen BGN como Acinetobacter baumannii, Pseudomonas aeruginosa y Enterobacterales, con escasas alternativas terapéuticas 3 , lo que ha llevado a la necesidad de reintroducir en la práctica clínica agentes antimicrobianos, como es el caso de colistín [5][6][7][8] . ...
... Colistín pertenece a la familia de las polimixinas (polimixina E), tiene actividad bactericida y presenta estrecho espectro de acción, con actividad anti-BGN, siendo utilizado principalmente en infecciones asociadas a la atención en salud. Fue introducido en la práctica clínica a finales de los años 50 y descontinuado por sus efectos adversos reportados, siendo paulatinamente reemplazado por alternativas terapéuticas más seguras, como las cefalosporinas 6,7 . No obstante, el incremento de las infecciones por microorganismos multirresistentes han hecho resurgir la necesidad de su uso. ...
... Respecto a los efectos adversos, sus manifestaciones más comunes son nefrotoxicidad y neurotoxicidad. La nefrotoxicidad es reversible y dosis-dependiente 7 ; no obstante, su frecuencia se habría reducido notoriamente en los estudios actuales en comparación a los años '60, bajando hasta incluso 10%, pero con abundante variación de acuerdo a cada estudio consultado 7,27,28 . Por su parte, la neurotoxicidad se manifiesta mayoritariamente en forma de parestesias, es bastante menos frecuente y también es reversible 6,27 . ...
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... 2 According to It was inserted into clinical practice in the mid 50's, but over the years its use was interrupted systematically with the growth of other active agents and Gram-negative bacteria, which were usually associated with manifestations of lower toxicity. 3 The colistin is a polypeptide antibiotic and has been known for decades for combating Gram-negative bacteria, but in its composition there are substances that make it an antibiotic with nephrotoxic effects. Despite these effects, their use was reevaluated again because of its efficacy against multi-drug resistant Gram-negative bacteria. ...
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Using clinical strains of multidrug resistant (MDR) Gram negative bacilli, we compared MICs obtained from both broth microdilution, the reference method, and sensi-disk elution method. We found that, with A. baumannii exception, results were very similar. Sensi-disk elution method could be a good and reliable alternative for colistin resistance determination.
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The dissemination of carbapenemase-producing Enterobacteriaceae is currently considered a serious clinical problem due to the failure in the treatment of infections produced by them. Among the carbapenemases, the enzyme KPC has spread worldwide and has been identified in the main enterobacterial species related with healthcareassociated infections, although Klebsiella pneumoniae is the predominant specie. The blaKPC gene is transported, mainly by the transposon Tn4401, detected in various enterobacterial species of different sequence types (ST) and geographical origin. In addition, new genetic platforms that are distinguished, from Tn4401 because of insertions or deletions of other genes have been described. Plasmids containing the blaKPC gene can be conjugative and mobilizable non-conjugative plasmids, and can carry other genetic determinants of resistance. The KPC-producing strains may have different levels of resistance to carbapenems, due to the involvement of additional mechanisms such as different expression levels of porins and efflux pumps associated with the production of extended spectrum β-lactamases and/or AmpC. However, the carbapenemases, with KPC as the most common enzyme, provide higher levels of resistance.