Prata nanoparticulada para o controle da mastite bovina causada por Staphylococcus aureus: validação de métodos analíticos e detecção em leite, músculo, rim e figado

• Ano de defesa: 2018
• Autor(a) principal: Renison Teles Vargas
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: nanopartículas de prata; validação; S aureus; ICP OES; mastite; Ciência animal
• Link de acesso: http://hdl.handle.net/1843/SMOC-B55PHL

Mastitis, the main disease of dairy herds, is responsible for up to 40% of all infectious diseases and significant economic losses due to decreased production, spending on medicines, veterinary services and milk disposal. In Brazil, the main pathogen that causes mastitis is Staphylococcus aureus, a microorganism that is difficult to control and resistant to most antimicrobials used in veterinary medicine. A new alternative to its control is based on the use of nanotechnology, which is more efficient than traditional antimicrobials, at much lower doses, thereby reducing the risks of residues in the milk and tissues of treated animals. In this sense, the work had three objectives. The first objective was the determination of MIC for S. aureus with commercial AgNp of 100 nm. For this, 23 samples of S. aureus were isolated at the Milk Microbiology Laboratory of Embrapa Dairy Cattle, in Juiz de Fora, MG, and evaluated on BHI Agar plates with different concentrations of AgNp. The MIC results showed that the minimum dose was 2.5 mg/mL, and that the traditional methodology suggested by the CLSI, using the MH broth, did not work for the MIC with AgNp. The second objective of the study was to validate a methodology for the detection of Ag in milk and in biological tissues (muscle, kidney and bovine liver). Milk and tissue samples, collected from animals negative for Ag residues, were fortified with known AgNp dosages. After drying in greenhouse, they were submitted to digestion and opening with HNO3 in the pre-digestion, associated to HCl during the heating process in a digester block. The samples were read on ICP - OES equipment. The results demonstrated that the proposed digestion method generates a good signal, with a standard deviation of less than 2%. The technique of digestion and reading of the samples is very efficient and with a tested sensitivity of at least 0.4975 ppb. The accuracy of the equipment is higher between 4.98 and 49.75 ppb for Ag detection. The criteria required by the legislation, such as Linearity, Selectivity, Accuracy, Detection Limit and Quantification Limit were met for all matrices evaluated. However, the method proved to be robust only for milk and bovine muscle. In relation to kidney and bovine liver, the method was sensitive to some changes in the standard methodology. The third objective of the study was to induce mastitis in six cows with one of the 23 S. aureus samples used in the MIC (sample 619) and then treated with AgNp at the dose determined by MIC. After the treatment, milk was collected for five days, and on the fifth day cow euthanasia was performed to collect samples to verify the presence of Ag residues. The results showed that intramammary application of AgNp in cows resulted in 50% clinical cure, evaluated by the presence of lumps during milking and clinical examinations. However, microbiological analyzes of the milk showed that there was no microbiological cure in 100% of the treated rooms. Regarding the presence of residues, after the fifth day of treatment, a high concentration of Ag was detected in the milk of the fourth treated mammary (PE) and in the liver of the six animals. In general, the proposed methodology was efficient and ICP-OES, a great option for determination of Ag in biological matrices. However, commercial 100 nm AgNPs were not effective for the control and treatment of S. aureus mastitis