Browsing by Author "Villagra, Nicolas A."

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    Porin alterations present in non-carbapenemase-producing Enterobacteriaceae with high and intermediate levels of carbapenem resistance in Chile
    (SOC GENERAL MICROBIOLOGY, 2012) Wozniak, Aniela; Villagra, Nicolas A.; Undabarrena, Agustina; Gallardo, Natalia; Keller, Nicole; Moraga, Marcela; Roman, Juan C.; Mora, Guido C.; Garcia, Patricia
    The main goal of this work was to identify the mechanisms responsible for carbapenem resistance in 61 Chilean clinical isolates of Enterobacteriaceae (Enterobacter spp., Serratia marcescens, Morganella morganii, Escherichia coli and Klebsiella pneumoniae) with reduced susceptibility to at least one carbapenem (ertapenem, imipenem or meropenem). All of the isolates were analysed for the presence of carbapenemases, extended spectrum beta-lactamases (ESBLs), AmpC enzymes and outer-membrane proteins. None of the isolates exhibited carbapenemase activity nor did they have any of the carbapenemase genes that were screened for. Most of the 61 strains produced at least one ESBL and/or one AmpC enzyme and either lost their porins or had altered porins according to sequence analysis. The distribution of ESBLs and AmpC enzymes was different among the species studied. Resistance in K. pneumoniae and E. coli isolates was associated with ESBLs; in M. morganii isolates, resistance was attributed to overexpression of an AmpC enzyme; and in Enterobacter spp. isolates, resistance was associated with both types of enzymes. In K. pneumoniae isolates, porin integrity was more a determinant of carbapenem resistance than the presence of ESBLs, whereas in isolates of Enterobacter spp., M. morganii and S. marcescens, the presence of an overexpressed AmpC enzyme was associated with higher imipenem and meropenem MIC values. Therefore, carbapenem resistance in Chilean isolates is not due to true carbapenemases but rather to a combination of porin loss/alteration and beta-lactamase activity. The fact that carbapenemases were not detected in this study is unique, given that many countries in the region have already reported the presence of these enzymes.
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    The carbon source influences the efflux pump-mediated antimicrobial resistance in clinically important Gram-negative bacteria
    (OXFORD UNIV PRESS, 2012) Villagra, Nicolas A.; Fuentes, Juan A.; Jofre, Matias R.; Hidalgo, Alejandro A.; Garcia, Patricia; Mora, Guido C.
    Multidrug efflux pumps are proteins known to play an important role in resistance in bacteria. These proteins are located in the inner membrane (IM), together with many other proteins, including inducible permeases that participate in the uptake of non-phosphotransferase system (PTS) carbohydrates (i.e. carbohydrates uptaken by mechanisms other than the PTS). However, lipid bilayer space in the IM is limited. Therefore, we examined whether the overexpression of unrelated IM proteins is able to interfere with the efflux-mediated resistance mechanism, consequently increasing the susceptibility towards different antimicrobial compounds.
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    Xylose Improves Antibiotic Activity of Chloramphenicol and Tetracycline against K. Pneumoniae and A. Baumannii in a Murine Model of Skin Infection
    (2018) Hidalgo, Alejandro A.; Arias, Angel J.; Fuentes, Juan A.; García Cañete, Patricia; Mora, Guido C.; Villagra, Nicolas A.