Browsing by Author "Silva, Daniela"
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- Insight into the efficiency of microalgae’ lipidic extracts as photosensitizers for Antimicrobial Photodynamic Therapy against Staphylococcus aureusPublication . Mendonça, Inês; Silva, Daniela; Conde, Tiago; Maurício, Tatiana; Cardoso, Helena; Pereira, Hugo; Bartolomeu, Maria; Vieira, Cátia; Domingues, M. Rosário; Almeida, AdelaideAntibacterial resistance causes around 1.27 million deaths annually around the globe and has been recognized as a top 3 priority health threat. Antimicrobial photodynamic therapy (aPDT) is considered a promising alternative to conventional antibiotic treatments. Algal lipid extracts have shown antibacterial effects when used as photosensitizers (PSs) in aPDT. In this work we assessed the photodynamic efficiency of lipidic extracts of microalgae belonging to different phyla (Bacillariophyta, Chlorophyta, Cyanobacteria, Haptophyta, Ochrophyta and Rhodophyta). All the extracts (at 1 mg mL−1) demonstrated a reduction of Staphylococcus aureus >3 log10 (CFU mL−1), exhibiting bactericidal activity. Bacillariophyta and Haptophyta extracts were the top-performing phyla against S. aureus, achieving a reduction >6 log10 (CFU mL−1) with light doses of 60 J cm−2 (Bacillariophyta) and 90 J cm−2 (Haptophyta). The photodynamic properties of the Bacillariophyta Phaeodactylum tricornutum and the Haptophyta Tisochrysis lutea, the best effective microalgae lipid extracts, were also assessed at lower concentrations (75 μg mL−1, 7.5 μg mL−1, and 3.75 μg mL−1), reaching, in general, inactivation rates higher than those obtained with the widely used PSs, such as Methylene Blue and Chlorine e6, at lower concentration and light dose. The presence of chlorophyll c, which can absorb a greater amount of energy than chlorophylls a and b; rich content of polyunsaturated fatty acids (PUFAs) and fucoxanthin, which can also produce ROS, e.g. singlet oxygen (1O2), when photo-energized; a lack of photoprotective carotenoids such as β-carotene, and low content of tocopherol, were associated with the algal extracts with higher antimicrobial activity against S. aureus. The bactericidal activity exhibited by the extracts seems to result from the photooxidation of microalgae PUFAs by the 1O2 and/or other ROS produced by irradiated chlorophylls/carotenoids, which eventually led to bacterial lipid peroxidation and cell death, but further studies are needed to confirm this hypothesis. These results revealed the potential of an unexplored source of natural photosensitizers (microalgae lipid extracts) that can be used as PSs in aPDT as an alternative to conventional antibiotic treatments, and even to conventional PSs, to combat antibacterial resistance.
- Microbial quality of edible seeds commercially available in southern PortugalPublication . Silva, Daniela; Nunes, Patrícia A.; Melo, Jessie; Quintas, CéliaIn the present work, the microbiological quality of sesame, flaxseed, chia, pumpkin sunflower seeds, a mix of seeds, as well as flaxseed flour, marketed in southern Portugal, were studied through the counting of aerobic microorganisms at 30 degrees C (AM), molds and yeast (M&Y), Escherichia coli (beta-glucuronidase positive) (beta-GP E. coli), Staphylococcus coagulase positive, and detection of Salmonella spp. The persistence of AM and M&Y populations were also counted in organic and non-organic flaxseed at 20 degrees C for 11 months. The seeds with the highest average of AM were flaxseed (1,3 x 10(6) CFU/g) followed by flaxseed flour (1,1 x 10(6) CFU/g) while the lowest level was found in chia (2,9 x 10(4) CFU/g). This seed also presented the lowest average values of filamentous fungi (9,8 x 10(2) CFU/g), whereas sunflower seeds had the highest levels (1,7 x 10(5) CFU/g). Flaxseed flour had the highest yeast counts (1,5 x 10(4) CFU/g). Although some samples had high levels of AM and fungi, beta-GP E. coli and Salmonella were not detected, therefore, they complied with the microbiological criteria of the European Union. The organic flaxseed contained higher numbers of AM and M&Y than the non-organic ones (p < 0.05). In addition, the storage of flaxseed at 20 degrees C resulted in changes of AM and M&Y, showing that these populations were able to remain viable after eleven months (AM Log 5.4-Log 5.6; M&Y Log 2.8 - Log 4.1). The results obtained in the present study, namely those high levels of AM and fungi (>10(6) and 10(4) CFU/g respectively), alert to the need of improving processing practices, storage/distribution conditions of edible seeds and derivatives, as well as the requirement of implementing adequate decontamination techniques.