Browsing by Author "Ulloa, María Teresa"
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Publication Antimicrobial Resistance Dynamics in Chilean Shigella sonnei Strains Within Two Decades: Role of Shigella Resistance Locus Pathogenicity Island and Class 1 and Class 2 Integrons(2022) Toro, Cecilia S.; Salazar, Juan Carlos; Montero, David A.; Ugalde, Juan; Díaz, Janepsy; Cádiz, Leandro A.; Henríquez, Tania; García, Camila; Díaz, Patricia; Camponovo, Rossanna; Hermosilla, Germán; Ulloa, María TeresaShigellosis is an enteric infectious disease in which antibiotic treatment is effective, shortening the duration of symptoms and reducing the excretion of the pathogen into the environment. Shigella spp., the etiologic agent, are considered emerging pathogens with a high public health impact due to the increase and global spread of multidrug-resistant (MDR) strains. Since Shigella resistance phenotype varies worldwide, we present an overview of the resistance phenotypes and associated genetic determinants present in 349 Chilean S. sonnei strains isolated during the periods 1995-1997, 2002-2004, 2008-2009, and 2010-2013. We detected a great variability in antibiotic susceptibility patterns, finding 300 (86%) MDR strains. Mobile genetic elements (MGE), such as plasmids, integrons, and genomic islands, have been associated with the MDR phenotypes. The Shigella resistance locus pathogenicity island (SRL PAI), which encodes for ampicillin, streptomycin, chloramphenicol, and tetracycline resistance genes, was detected by PCR in 100% of the strains isolated in 2008-2009 but was less frequent in isolates from other periods. The presence or absence of SRL PAI was also differentiated by pulsed-field gel electrophoresis. An atypical class 1 integron which harbors the bla OXA-1 -aadA1-IS1 organization was detected as part of SRL PAI. The dfrA14 gene conferring trimethoprim resistance was present in 98.8% of the 2008-2009 isolates, distinguishing them from the SRL-positive strains isolated before that. Thus, it seems an SRL-dfrA14 S. sonnei clone spread during the 2008-2009 period and declined thereafter. Besides these, SRL-negative strains harboring class 2 integrons with or without resistance to nalidixic acid were detected from 2011 onward, suggesting the circulation of another clone. Whole-genome sequencing of selected strains confirmed the results obtained by PCR and phenotypic analysis. It is highlighted that 70.8% of the MDR strains harbored one or more of the MGE evaluated, while 15.2% lacked both SRL PAI and integrons. These results underscore the temporal dynamics of antimicrobial resistance in S. sonnei strains circulating in Chile, mainly determined by the spread of MGE conferring MDR phenotypes. Since shigellosis is endemic in Chile, constant surveillance of antimicrobial resistance phenotypes and their genetic basis is a priority to contribute to public health policies.Item Cepas chilenas de origen clínico de Vibrio cholerae no-O1, no-O139 portan los genes vcsN2, vcsC2, vcsV2, vspD, toxR2 y vopF del sistema de secreción T3SS2 presentes en una isla de patogenicidad(2019) Ulloa, María Teresa; Sanhueza, Camila; Henríquez, Tania; Aguayo, Benjamín; Hermosilla, Germán; Porte, Lorena; Dabanch, Jeannette; Braun, Stephanie; Fica, Alberto; Briceño, Isabel; Osorio, CarlosBackgound: The virulence factors of the Vibrio cholerae non-O1, non-O139 strains are not clearly known. The strain of septicemic origin NN1 Vibrio cholerae non-O1, non-O139 was sequenced previously by the Illumina platform. A fragment of the pathogenicity island VPaI-7 of V. parahaemolyticus was detected in its genome. Aim: To detect the virulence genes vcsN2, vcsC2, vcsV2, vspD, toxR2 y vopF in Chilean strains of V. cholerae non-O1, non-O139. Methods: A total of 9 Chilean strains of clinical origin of Vibrio cholerae non-O1, non-O139 isolated between 2006-2012 were analyzed by conventional PCR assays for type III secretion genes encoded on that island: vcsN2, vcsC2, vcsV2, vspD, toxR2 and vopF. Additionally, the presence of the virulence genes hylA and rtxA was determined. In addition, REP-PCR and ERIC-PCR assays were performed. Results: most (6/9) Chilean V. cholerae non-O1, non-O139 strains contain the type III secretion genes vcsN2, vcsC2, vcsV2, vspD, toxR2 and vopF, encoded in an island of pathogenicity. In addition, all (9/9) the strains contain the virulence genes hylA and rtxA. Conclusion: These results strongly suggest the possibility that those strains possess an important virulence potential in humans.Publication Mechanical and antimicrobial properties of low-density-polyethylene/MgO nanocomposites(2022) Cament, Alejandro; Moreno-Serna, Viviana; Loyo, Carlos; Quintana, Pabla; Seura, Pablo; Vallejos Baier, Raúl; Benavente, Rosario; Ulloa, María Teresa; Rivas, Lina; Pino, Eduardo; Gómez, Tatiana; Zapata, Paula A.Low-density polyethylene (LDPE) nanocomposites containing magnesium oxide (MgO) nanoparticles are obtained by melt mixing. MgO nanoparticles ca. 29 ± 2 nm are synthesized by sol–gel and organically modified on the surface with oleic acid (Mod-MgO), whose final concentration in the polymers is 3, 5, and 10 wt%. The presence of these nanoparticles did not affect the crystallization process of LDPE. However, Young's modulus increases with 10 wt% of Mod-MgO nanoparticles, rendering higher reinforcement effects with an increase as high as 48%. This affects the elongation at break, which decreases ca. 57% compared to neat LDPE. The storage and loss modulus of the LDPE/MgO and LDPE/Mod-MgO nanocomposites increases at room temperature and low temperatures ( 150 to 50C) compared to neat LDPE. SEM analysis showed that the organic modification of MgO nanoparticles improved their dispersion within the polymer matrix. Nanocomposites present antimicrobial properties against Escherichia coli, reaching an efficiency ca. 53%.Publication PLA/CaO nanocomposites with antimicrobial and photodegradation properties(2022) Loyo, Carlos; Moreno-Serna, Viviana; Fuentes, Jairo; Amigo, Nicolás; Sepúlveda, Francesca Antonella; Ortiz, Andrés; Rivas, Lina; Ulloa, María Teresa; Benavente, Rosario; Zapata , Paula A.CaO nanoparticles sized ca. 26 nm were organically modified with oleic acid (Ol-CaO), and both were incorporated into PLA at concentrations of 5 and 8 wt.% by a melting process. Modification of nanoparticles improved the distribution into PLA, as seen by transmission electron microscopy (TEM). Thermal analysis revealed that the presence of Ol-CaO in the PLA matrix promoted a decrease ca. 13% in the glass transition temperature (Tg). The thermal stability of the PLA/Ol-CaO decreased ca. 23% compared to the neat PLA due to the catalytic activity from nanoparticles, while Vickers Microhardness (HV) for nanocomposites PLA/Ol-CaO increased ca. 9%, compared with the neat PLA, due to the good dispersion of modified-surface Ol-CaO nanoparticles in PLA. PLA/Ol-CaO nanocomposites reached 99.9% of antimicrobial effectiveness against E. coli for nanoparticles content above 8 wt.%. From photodegradation tests under irradiation during five days, it was verified that the presence of CaO nanoparticles accelerated the photodegradation of the polymer matrix nanoparticles into PLA promoted a decreasing ca. 13% of Tg and an increase in the degree of crystallinity (Xc) (ca. 7%), compared to PLA/CaO without irradiation. Besides, the viscosity molecular weight (M¯ v) of PLA/CaO showed a higher decrease than neat PLA after irradiation, and SEM analysis showed that the nanocomposites presented cavities around the nanoparticles after irradiation. Our results showed that incorporating CaO nanoparticles into the PLA polymer matrix allows future development of more sustainable materials as nanocomposites for food packaging or medical devices.