Fluorescence-Linked Aptamer Assay for SARS-CoV-2 Spike-Protein: A Step-by-Step Performance Analysis in Clinical Samples.

The COVID-19 pandemic has been a main concern over the last two years and has become one of the most important crises in the history of human health. Today, there is still a need for affordable and reliable diagnostic tests for massive disease monitoring. Previously, a set of highly specific DNA-aptamers (C7/C9) binding to the SARS-CoV-2 Spike (S) protein were isolated but its performance in clinical samples remained to be tested. Here, 242 samples were collected through three different methods and subjected to florescence-linked aptamer assays (FLAA) based on C7/C9 aptamers through two readout protocols. Then, a step-by-step statistical approach which included agreement tests, proportion comparisons and binomial and multinomial logistic regressions was used to predict optimal conditions for the novel C7/C9 FLAA test. RTqPCR threshold cycles, symptoms onset and processing time were influential factors on FLAA test results. Naturally occurring mutations on S were also detected and analyzed. Aminoacidic substitutions D614G and T732A appeared relevant for aptamer recognition although further studies are necessary. The methodology presented here is the first step to determine the performance and diagnosis across a range of clinical contexts and it might serve as a base for a complete analysis applicable to other designs of new diagnostic tests.

Simplified modeling of E. coli mortality after genome damage induced by UV-C light exposure.

UV light is a group of high-energy waves from the electromagnetic spectrum. There are three types of UV radiations: UV-A, -B and -C. UV-C light are the highest in energy, but most are retained by the ozone layer. UV-A and -B reach the earth's surface and cause damage on living organisms, being considered as mutagenic physical agents. Numerous test models are used to study UV mutagenicity; some include special lamps, cell cultures and mathematical modeling. Mercury lamps are affordable and useful sources of UV-C light due to their emission at near the maximum absorption peak of nucleic acids. E. coli cultures are widely used because they have DNA-damage and -repairing mechanisms fairly similar to humans. In here we present two simple models that describe UV-C light incidence on a genome matrix, using fundamental quantum-mechanical concepts and considering light as a particle with a discontinuous distribution. To test the accuracy of our equations, stationary phase cultures of several E. coli strains were exposed to UV-C light in 30 s-intervals. Surviving CFUs were counted and survival/mortality curves were constructed. These graphs adjusted with high goodness of fit to the regression predictions. Results were also analyzed using three main parameters: quantum yield, specific speed and time of mortality.

Antimutagenic activity of vitamin B1 against damages induced by chemical and physical mutagens in Salmonella typhimurium and Escherichia coli.

Thiamine (vitamin B1) is an essential nutrient acting mainly as an enzymatic cofactor on diverse cell processes. It has been reported that vitamin B1 has a significant role in the signaling pathways related to the response to adverse environmental conditions (chemical and physical). The objectives of this study were to evaluate the antimutagenic potential of vitamin B1 in front of DNA-alkylating agents in the presence/absence of ogt and ada repairing genes in Salmonella typhimurium strains and against damage induced by ultraviolet light type C in Escherichia coli strains mutated at the uvrABC system and recBCD enzymes. For S. typhimurium, an antimutagenesis test (Ames test) was performed using strains deficient in one or both genes (YG7100 ada-/ogt+, YG7104 ada+/ogt-, YG7108 ada-/ogt-). For E. coli, mutated strains (K-12 derived strains Hfr H180 uvrB+/recA+, W3110 uvrB+/recA- and ATCC®8739 uvrB-/recA+) were exposed to UV-C light at different time intervals, with and without vitamin B1. Our results showed that thiamine is an antimutagen against methyl-N-nitro-N-nitrosoguanidine or ethyl-N-nitro-N-nitrosoguanidine only when the ogt gene is present. While for E. coli, the presence of vitamin B1 increased the survival rate, implying an antimutagenesis independent of uvrABC repairing system and recBCD enzymes.