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- Study of antimicrobial activity and atomic force microscopy imaging of the action mechanism of cashew tree gumPublication . Campos, Débora A.; Ribeiro, Alexandra C.; Costa, Eduardo M.; Fernandes, João C.; Tavaria, Freni K.; Araruna, Felipe Bastos; Eiras, Carla; Eaton, Peter; Leite, José Roberto S. A.; Pintado, M. ManuelaThe aim of this work was to evaluate the antimicrobial potential of two grades of cashew tree gum (crude and purified) against eight microorganisms and to analyze the mechanism of cashew tree gum antimicrobial action via atomic force microscopy (AFM) imaging. The results indicated strong antimicrobial properties of pure cashew tree gum against all tested microorganisms, except for Candida albicans and Lactobacillus acidophilus. On the other hand crude cashew gum showed antimicrobial activity only against Gram-positive bacteria (MRSA, MSSA, Listeria innocua and Enterococcus faecium). Atomic force microscopy imaging showed that pure cashew tree gum lead to bacterial cell collapse. In conclusion cashew tree gum presented relevant antimicrobial activity against most of the studied bacteria, and the purification of the cashew gum affected its antimicrobial spectrum.
- Chitosan-based silver nanoparticles: a study of the antibacterial, antileishmanial and cytotoxic effectsPublication . Lima, Douglas dos Santos; Gullon, Beatriz; Cardelle-Cobas, Alejandra; Brito, Lucas M.; Rodrigues, Klinger A. F.; Quelemes, Patrick V.; Ramos-Jesus, Joilson; Arcanjo, Daniel D. R.; Plácido, Alexandra; Batziou, Krystallenia; Quaresma, Pedro; Eaton, Peter; Delerue-Matos, Cristina; Carvalho, Fernando Aecio; Silva, Durcilene Alves da; Pintado, M. E.; Leite, José Roberto de SáSilver nanoparticles have been studied as an alternative for treatment of microbial infections and leishmaniasis, without promoting induction of microbial or parasite resistance. In this study, chitosan-based silver nanoparticles were synthesized from silver nitrate (AgNO3), sodium borohydride as a reducing agent, and the biopolymer chitosan as a capping agent. The chitosan-based silver nanoparticles were characterized by ultraviolet-visible, Fourier transform infrared, dynamic light scattering, zeta potential, atomic force microscopy, and transmission electron microscope. The antibacterial assay was performed by determination of the minimum inhibitory concentration. The antileishmanial and the cytotoxic effects induced by AgNO3, chitosan, and chitosan-based silver nanoparticles were analyzed by resazurin and MTT colorimetric assays, respectively. AgNO3, chitosan, and chitosan-based silver nanoparticles induced a marked activity against all bacterial strains and promastigote forms of Leishmania amazonensis at minimum inhibitory concentrations ranging from 1.69 to 3.38 μg Ag/mL. Interestingly, the chitosan-based silver nanoparticles presented less cytotoxicity than the AgNO3 alone and were more active against L. amazonensis than solely chitosan. Furthermore, the cytotoxic concentrations (CC50) of both chitosan and chitosan-based silver nanoparticles against macrophages were significantly higher than the IC50 against promastigotes. Thus, the chitosan-based silver nanoparticles represent a promising alternative for the treatment of microbial infections and leishmaniasis.
- Evaluation of chitoligosaccharides effect upon probiotic bacteriaPublication . Fernandes, João C.; Eaton, Peter; Franco, Isabel; Ramos, Óscar S.; Sousa, Sérgio; Nascimento, Henrique; Gomes, Ana; Santos-Silva, Alice; Xavier, Malcata F.; Pintado, Manuela E.The main objective of the present study was to evaluate the antibacterial effect – through the determination of minimum inhibitory (and lethal) concentrations, as well as the possible prebiotic potential of chitooligosaccharides (COS) – through the determination of growth curves, on Bifidobacterium animalis Bb12, Bifidobacterium animalis Bo and Lactobacillus acidophilus Ki. Atomic force microscopy was further used to obtain high resolution images of COS effects upon the cell morphology. Our results demonstrate that COS do not stimulate the growth of those strains, neither the strains are capable of using COS as a primary source of carbon. Analysis of morphology when exposed to inhibitory/bactericidal concentrations, suggested that COS do not exert any direct damage upon the bacteria structure, instead the bacteria are apparently covered by COS, which likely prevent nutrient uptake.
- Antioxidant activity of chitooligosaccharides upon two biological systems: erythrocytes and bacteriophagesPublication . Fernandes, João C.; Eaton, Peter; Nascimento, Henrique; Gião, Maria S.; Ramos, Oscar. L.; Belo, Luís; Santos-Silva, Alice; Pintado, Manuela E.; Malcata, F. XavierMost of the reports to date on the antioxidant capacity of chitosans and chitooligosaccharides (COS) are based on strictly chemical methods. When studying antioxidants with potential in vivo applications, the method used to evaluate the antioxidant activity should be representative of the conditions in which the antioxidant might have a protective effect. In this work we evaluate the antioxidant activity of two COS mixtures and a low MW chitosan (LMWC) upon two biological oxidizable substrates – erythrocytes and phages, subjected to accelerated oxidation conditions. Our results suggest that COS/LMWC can be used as antioxidants in biological systems. All the tested compounds reduced either the hemolytic and DNA damage, by inhibiting H2O2- and AAPH-radicals. However, the results obtained for these biological assays did not reveal a dose dependence, contrary to the chemical assay, suggesting that the protective concentrations should be established, in order to prevent enhancement of the oxidative damage – i.e. a prooxidant effect.