Desenvolvimento de itens de ensaio de proficiência para pesquisa de Salmonella spp. em matriz chocolate

The aim of this study was to develop lyophilized test items (TI) containing Salmonella spp., in chocolate matrix to be used in proficiency testing programs (PTP). Microbial analysis was conducted on samples of granulated chocolate to verify that the sample was free of the target microorganisms. Homogeneity and stability studies in long and short term were carried out to monitor TI quality; the presence of vacuum in the samples was also verified, to ensure the efficiency of the lyophilization process. The results of the microbial testing indicated no contamination by Salmonella spp.; thus, the sample was appropriate to be used as matrix. The lyophilization technique, using trehalose as cryoprotectant, has proven to be effective for desiccation of TI produced. The Salmonella batch proved to be sufficiently homogeneous, because the microorganism was present in all analyzed flasks. The batch was held stable at -20°C (five weeks) and -70°C (26 weeks). As for the transportation stability, the batch was considered stable at 4°C (in four days). The TI produced batch in this study showed a quality level that makes it suitable to be used in PTP, to contribute to the increasing reliability of the test results from laboratories and to provide subsidies for identification of problems and troubleshooting.O objetivo desse estudo foi desenvolver itens de ensaio (IE) liofilizados contendo Salmonella spp., em matriz chocolate, para utilização em ensaio de proficiência (EP). Foi realizada a análise microbiológica de uma amostra de chocolate granulado para verificar se estava livre do micro-organismo alvo. Para monitoramento da qualidade dos IE, realizou-se estudos de homogeneidade e estabilidade em longo e curto prazo, bem como verificou-se a presença de vácuo nas amostras garantindo a eficiência do processo de liofilização. A análise microbiológica do chocolate indicou ausência de contaminação por Salmonella spp., estando apto para ser utilizado como matriz. A técnica de liofilização, com uso de trealose como crioprotetor, se mostrou eficaz para dessecação dos IE produzidos. O lote produzido se apresentou suficientemente homogêneo, pois o micro-organismo estava presente em todos os frascos analisados. O lote se apresentou estável à temperatura de -20ºC (em cinco semanas) e -70ºC (em 26 semanas); na estabilidade de transporte, foi considerado estável a 4ºC (em quatro dias). O lote de IE produzido nesse estudo apresentou qualidade que o torna apto para uso em EP, o que visou contribuir para o aumento da confiabilidade dos resultados das análises dos laboratórios e propiciar subsídios para a identificação e solução de problemas

Search for dark matter produced in association with bottom or top quarks in √s = 13 TeV pp collisions with the ATLAS detector

A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fb−1 of proton–proton collision data recorded by the ATLAS experiment at √s = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements