Decline in Mycobacterium bovis and Brucella abortus populations during the maturation of experimentally contaminated parmesan-type cheese

Abstract

Decline in Mycobacterium bovis AbstractBrazilian legislation allows the manufacture of raw milk cheese with a maturation exceeding 60 days at room temperature above 5°C, but there is a lack of solid scientific evidence on the efficacy of this maturation process in inactivating important pathogens that may be present in milk, such as Mycobacterium bovis and Brucella abortus. Thus, the objectives of this study were to produce parmesantype cheese experimentally contaminated with M. bovis and B. abortus and evaluate the survival of these pathogens along 2-month maturation. Parmesan-type cheese was manufactured in the laboratory using whole pasteurized milk with or without inoculation with M. bovis (SB1033) or B. abortus (1119-3) and matured at 18°C for up to 63 days. M. bovis was inoculated in Stonebrink-Leslie medium supplemented with antibiotics and incubated at 37°C for 45 days, and B. abortus was incubated in Farrel medium at 36°C for 3 days. The average D 18°C value, weighted by variance, was 37.5 ± 5.3 days for M. bovis and 5.9 ± 0.7 days for B. abortus. The average physicochemical parameters in the cheese at the end of the study were as follows: pH = 4.89, water activity = 0.976, and moisture percentage = 43.1%. The pH might have contributed to the reduction in the population of B. abortus but seems not to have significantly influenced the population of M. bovis. We conclude that the duration of the maturation process influences the size of the surviving populations of M. bovis and B. abortus, and that the shortening of the maturation duration might not ensure a decline in pathogen levels to safe levels. Thus, complementary studies considering the effect of several other technological aspects on the survival of these pathogens are required, including the effect of the lactic acid bacterial population, salt content, and temperature of maturation. ResumoA legislação brasileira permite a fabricação queijos de leite cru com maturação superior a 60 dias em temperatura acima de 5°C, mas falta evidência científica sólida sobre a eficácia do processo de maturação na inativação de importantes patógenos que podem estar presentes no leite, como o Mycobacterium bovis e a Brucella abortus. Assim, os objetivos desse estudo foram produzir o queijo tipo parmesão experimentalmente contaminado com M. bovis e B. abortus e avaliar a sobrevivência desses patógenos ao longo de 2 meses de maturação. Queijo do tipo parmesão foi fabricado em laboratório com leite pasteurizado integral com ou sem inoculo de M. bovis (SB1033) ou B. abortus (1119-3) e maturado a 18°C por até 63 dias. M. bovis foi semeado em meio Stonebrink-Leslie, acrescido de antibióticos, e incubado a 37°C por 45 dias e a B. abortus foi semeada em meio Farrel a 36°C por 3 dias. O valor D 18°C médio, ponderado pela variância, foi de 37,5 ± 5,3 dias para o M. bovis e de 5,9 ± 0,7 dias para a B. abortus. Os parâmetros físico-químicos médios do queijo no final do estudo foram como se segue: pH = 4,89, atividade de água = 0,976 e umidade percentual = 43,1%. O pH pode ter ...

Mycobacteria in Minas cheese commercialized in open fairs in São Paulo, Brazil

“…Variable results regarding the ability to detect M. bovis in examined samples may be attributable to a range of factors that influence the sensitivity and specificity of the different protocols used. These factors include the low prevalence of the disease in the Brazilian bovine herd (BAHIENSE et al, 2016;BARBIERI et al, 2016;DIAS et al, 2016;GALVIS et al, 2016;GUEDES et al, 2016;LIMA et al, 2016;NÉSPOLI et al, 2016;QUEIROZ et al, 2016;RIBEIRO et al, 2016;ROCHA et al, 2016;VELOSO et al, 2016;VENDRAME et al, 2016), the dilution effect of contaminated milk mixed with uncontaminated milk, the low multiplication probability of the initial microbial population in milk as a function of storage time and temperature, the reduction in contaminant load during production and curing (STARIKOFF et al, 2016), and the lack of a validated research method for M. bovis in food products that enables the detection of low levels of mycobacteria in high levels of other microorganisms. The presence of this accompanying microbiota calls for sample decontamination, which, by causing injury in bacterial cells, might also have hindered the detection of M. bovis (CORNER et al, 1995).…”