RESUMEN La quitina es un polisacárido lineal producido por especies animales y fúngicas. Una de sus principales fuentes de obtención es el hongo Aspergillus niger, cultivado en biorreactores industriales. Es un biopolímero neutro que modifica las propiedades eléctricas de los materiales compuestos, una característica muy útil para algunos dispositivos electrónicos. Nuestro objetivo en este trabajo fue la caracterización fisicoquímica de películas de quitina, extraída de dicho hongo por un método químico asistido por ondas de choque y calor, así como también determinar su resistividad eléctrica al aplicarle altos voltajes (entre 10 y 20 kV). Las ondas de choque se utilizaron en este estudio porque se sabe que inducen poros en las células y podrían promover la entrada de álcali en la hifa, permitiendo una mejor eliminación de los componentes celulares residuales. La quitina fue neutralizada, secada y se formaron películas. Los valores de proteína residual se cuantificaron con la técnica de ácido bicinconínico (BCA), obteniendo películas con bajas cantidades de proteína. La caracterización del morfotipo específico extraído se estimó mediante infrarrojo transformado de Fourier (FTIR) y difracción de rayos X (XRD). Para evaluar la resistividad ante voltajes elevados, se diseñó un circuito especial que permitió detectar variaciones significativas de esta con respecto al voltaje aplicado, es decir, la quitina mostró un comportamiento coincidente con un varistor no lineal y, hasta donde sabemos, este es el primer informe de dicho comportamiento para la quitina.

ABSTRACT Chitin is a linear polysaccharide produced by animal and fungal species. One of its sources is the fungus Aspergillus niger, which is culturable in industrial bioreactors. Chitin is a neutral biopolymer that modifies the electrical properties of composite materials. These are useful features in some electronic devices. This study aimed to carry out physicochemical characterizations of chitin films obtained from the above-mentioned fungus, using a chemical method enhanced with exposure to heat and shock waves, and to determine their electrical resistivity at high voltages (between 10 and 20 kV). Shock waves were used in this study because they are known to induce pores into cells and could promote alkali entry into the hypha, allowing better removal of residual cellular components. Chitin was neutralized, dried, and films were produced. Residual protein values were quantified by bicinchoninic acid assay (BCA). The films obtained had low amounts of protein. The characterization of the specific morphotype extracted was done by FTIR and XRD. An especially designed circuit revealed significant variations of the resistivity as the voltage was varied. This behavior is typical of a non-linear varistor and, to the best of our knowledge, has not been reported for chitin.

Abstract Multidrug-resistant microorganisms are of great concern to public health. Genetic mobile elements, such as plasmids, are among the most relevant mechanisms by which bacteria achieve this resistance. We obtained an Escherichia coli strain CM6, isolated from cattle presenting severe diarrheic symptoms in the State of Querétaro, Mexico. It was found to contain a 70 kb plasmid (pMEX01) with a high similarity to the pHK01-like plasmids that were previously identified and described in Hong Kong. Analysis of the pMEX01 sequence revealed the presence of a blaCTX-M-14 gene, which is responsible for conferring resistance to multiple β-lactam antibiotics. Several genes putatively involved in the conjugative transfer were also identified on the plasmid. The strain CM6 is of high epidemiological concern because it not only displays resistance to multiple β-lactam antibiotics but also to other kinds of antibiotics.