Browsing by Author "Mora, Guido C."

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    Inactivation of Glutamine Synthetase-Coding Gene glnA Increases Susceptibility to Quinolones Through Increasing Outer Membrane Protein F in Salmonella enterica Serovar Typhi
    (2020) Millanao, Ana R.; Mora, Aracely Y.; Saavedra, Claudia P.; Villagra, Nicolas A.; Mora, Guido C.; Hidalgo, Alejandro A.
    Ciprofloxacin is the choice treatment for infections caused by Salmonella Typhi, however, reduced susceptibility to ciprofloxacin has been reported for this pathogen. Considering the decreased approbation of new antimicrobials and the crisis of resistance, one strategy to combat this problem is to find new targets that enhances the antimicrobial activity for approved antimicrobials. In search of mutants with increased susceptibility to ciprofloxacin; 3,216 EZ-Tn5 transposon mutants of S. Typhi were screened. S. Typhi zxx
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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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    Spectral, theoretical characterization and antifungal properties of two phenol derivative Schiff bases with an intramolecular hydrogen bond
    (2015) Carreño, Alexander; Gacitúa Santelices, Manuel Alejandro; Páez Hernández, Dayan; Polanco, Rubén; Preite, Marcelo Daniel; Fuentes, Juan A.; Mora, Guido C.; Chávez Madariaga, Ivonne; Arratia Pérez, Ramiro
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    The Salmonella Typhi hlyE gene plays a role in invasion of cultured epithelial cells and its functional transfer to S. Typhimurium promotes deep organ infection in mice
    (2008) Fuentes, Juan A.; Villagra, Nicolas; Castillo-Ruiz, Mario; Mora, Guido C.
    Comparison of genome sequences of Salmonella enterica serovars Typhi and Typhimurium reveals that S. Typhi has a small 2.3 kb genomic island missing in S. Typhimurium, designated Salmonella pathogenicity island 18 (SPI-18), which includes two potential genes. One of these, hlyE, encodes a hemolysin related to the Escherichia coli K12 HlyE hemolysin. PCR assays show that SPI-18 is present in S. Typhi and in many other, but not all, serovars of S. enterica subsp. enterica belonging to the SARB collection. HlyE activity cannot be detected in S. Typhi by means of standard plate assays. Nevertheless, we were able to reveal this activity upon lysis of bacterial cells with phages, in the presence of ampicillin, and in a ompA genetic background, conditions that compromise the integrity of the bacterial envelope. Almost all serovars of the SARB collection shown to cause systemic infections in humans have SPI-18 and hlyE and express an active hemolysin revealed upon bacterial envelope destabilization. S. Typhi hlyE mutants are impaired in invasion of human epithelial cells in vitro, and its heterologous expression in S. Typhimurium improves the colonization of deep organs in mice, demonstrating that the HlyE hemolysin is a new virulence determinant. (C) 2008 Published by Elsevier Masson SAS.
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    The capacity of Salmonella to survive inside dendritic cells and prevent antigen presentation to T cells is host specific
    (WILEY-BLACKWELL, 2008) Bueno, Susan M.; Gonzalez, Pablo A.; Carreno, Leandro J.; Tobar, Jaime A.; Mora, Guido C.; Pereda, Cristian J.; Salazar Onfray, Flavio; Kalergis, Alexis M.
    Infection with Salmonella enterica serovar Typhimurium (S. Typhimurium) causes a severe and lethal systemic disease in mice, characterized by poor activation of the adaptive immune response against Salmonella-derived antigens. Recently, we and others have reported that this feature relies on the ability of S. Typhimurium to survive within murine dendritic cells (DCs) and avoid the presentation of bacteria-derived antigens to T cells. In contrast, here we show that infection of murine DCs with either S. Typhi or S. Enteritidis, two serovars adapted to different hosts, leads to an efficient T-cell activation both in vitro and in vivo. Accordingly, S. Typhi and S. Enteritidis failed to replicate within murine DCs and were quickly degraded, allowing T-cell activation. In contrast, human DCs were found to be permissive for survival and proliferation of S. Typhi, but not for S. Typhimurium or S. Enteritidis. Our data suggest that Salmonella host restriction is characterized by the ability of these bacteria to survive within DCs and avoid activation of the adaptive immune response in their specific hosts.
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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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    The cotranscribed Salmonella enterica sv. Typhi tsx and impX genes encode opposing nucleoside-specific import and export proteins
    (2006) Bucarey, Sergio A.; Villagra, Nicolas A.; Fuentes, Juan A.; Mora, Guido C.
    The Salmonella, enterica tsx gene encodes a nucleoside-specific outer membrane channel. The Tsx porin is essential for the prototrophic growth of S. enterica sv. Typhi in the absence of nucleosides. RT-PCR analysis shows that the tsx gene is cotranscribed with an open reading frame unique to S. enterica, impX (STY0450), which encodes an inner membrane protein 108 amino acids in length, which is predicted to have only two transmembrane a-helices. Fusions of the lacZgene to both tsx and impX reveal that the transcription of both genes is induced in the presence of adenosine. A null mutation in the S. Typhi impX gene suppresses the induced auxotrophy for adenosine or thymidine resulting from a tsx mutation and confers sensitivity to high concentrations of adenosine or thymidine. The ImpX protein, when tagged with a 3xFLAG epitope, is functional and associates with the inner membrane; impX mutants are defective in the export of H-3-radiolabeled thymidine. Taken together, these and other results suggest that the S. Typhi Tsx porin and ImpX inner membrane protein facilitate competing mechanisms of thymidine influx and efflux, respectively, to maintain the steady state levels of internal nucleoside pools.
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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.