Efeito do antagonismo in vitro de bactérias ácido-láticas e da maturação na sobrevivência de brucella abortus em queijos tipo Minas artesanal

• Ano de defesa: 2018
• Autor(a) principal: Jamili Maria Suhet Mussi
• Tipo de documento: Tese
• Tipo de acesso: Acesso aberto
• Idioma: por
• Instituição de defesa: Universidade Federal de Minas Gerais; UFMG
• Palavras-chave em Português: segurança alimentar; leite cru; microbiota do leite; Queijos; bactérias ácido-láticas; maturação; brucelose; Ciência animal
• Link de acesso: http://hdl.handle.net/1843/SMOC-B4RNEK

Brucellosis has global importance and the occurrence in the human population is directly related to the prevalence of the disease in animals. In Brazil, Brucella abortus is endemic in cattle, with a heterogeneous distribution between the states. The shedding of Brucella spp. in the milk of infected animals makes this food a source of infection for humans. In addition, Brucella spp. can survive on various dairy products, including ripeness cheeses produced with raw milk, even if this process causes physical-chemical and microbiological alterations in cheese, which may lead to the reduction of pathogens. The Minas artisanal cheese is produced with bovine raw milk, endogenous starter culture and is matured for a variable period, depending on the micro-region of Minas Gerais state where it is produced. The presence of acid lactic bacteria (LAB) in this product has been increased its food safety, since previous studies have demonstrated the potential of LAB in the inhibition of pathogens of public health importance, by producing antimicrobial substance under in vitro and in vivo assays. Thus, this thesis is composed of two experiments: the first aimed to evaluate methods for in vitro study of the antimicrobial activity of LAB against B. abortus and to evaluate the antagonistic effect of LAB on viability of this pathogen. The second experiment aimed to evaluate the effect of maturation on the survival of B. abortus in Minas artisanal cheese. For the first experiment, 18 LAB strains isolated from Minas artisanal cheese from three regions (Canastra, Campos das Vertentes and Araxá), Minas Gerais, Brazil, were tested against three isolates of B. abortus (2308, 544 and 2683), using three methodologies: spot-on-the-lawn, agar well diffusion assay and antagonistic activity of the culture supernatants. The results showed that: only the acid lactic bacteria culture supernatants allowed the study of the in vitro antagonism of LAB against B. abortus and the B. abortus growth was totally inhibited by almost all LAB isolates tested (13/18), except when the supernatants were neutralized (pH 7.0). The second experiment was composed of three experimental groups: 103 CFU/mL B. abortus, 106 CFU/mL B. abortus and negative control group. B. abortus 2308 was inoculated in the milk at concentrations determined in experimental group. Subsequently, 2% of endogenous starter culture was added to the cheeses, which were matured in BOD at 22.5 ° C and evaluated in 7 ripeness periods (1, 8, 15, 22, 29, 45, 60 days). The B. abortus viability was determined by techniques the counting of drop counting method, direct plating of 1mL and pre-enrichment. Cheeses from the negative control group were analyzed for coliform counts at 30 °C, E. coli, Staphylococcus coagulase positive and negative, lactic acid bacteria, molds and yeasts, presence of Salmonella spp, percentage of total dry extract, moisture, fat, total protein, chloride and pH. A survival analysis was performed to evaluate the decrease of B. abortus concentration during ripening time. The influence of microbiological and physico-chemical variables on the survival of B. abortus in cheeses during ripening was evaluated by a Poisson regression using generalized estimating equations (GEE). The results found for treatment with 103 UFC/mL of B. abortus, demonstrated that between 8 and 15 days of ripeness, the pathogen was no longer detected. For 106 UFC/mL of B. abortus, between 22 and 29 days of ripeness were necessary for the innocuity of the Minas artisanal cheese experimentally inoculated. The percentage of moisture, fat in the dry extract and total protein in the cheeses were related to the survival of B. abortus. Together these two experiments demonstrated the importance of acid lactic bacteria and the ripeness process in reducing the viability of B. abortus, contributing to the food safety of the Minas artisanal cheese