RESUMO
The ability of a yogurt starter culture formed by Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp bulgaricus to inhibit the growth of four enterotoxin type A and B producers Staphylococcus aureus strains (ATCC 6538, S6, FRI-100 and a strain isolated from milk) during fermentation of milk and subsequent storage was investigated. Sterile skim milk was inoculated with about 10(6) CFU/ml of S. aureus and with about 10(6) CFU of starter culture, and incubated at 42 degrees C during 8 h, followed by refrigeration at 4 degrees C. Samples were taken every 2 h during fermentation and every 2 days during storage. Viable count of lactic acid bacteria and S. aureus as well as pH, acidity, thermostable deoxyribonuclease (TNase) and staphylococcal enterotoxin A (SEA) production were evaluated. Behavior of four strains was similar; S. aureus survived the 8 h fermentation with LAB, and its population began to decrease from the first day of storage, being completely inhibited at 9-10 days. TNase and SEA production were positive in all samples taken along the study. It was demonstrated that enterotoxigenic strains of S. aureus were able to survive the fermentation of milk with a yogurt starter culture and they were inhibited after several days during storage of the fermented product, contrary to the general belief which considered it very difficult due to the low pH. Even though S. aureus was inhibited, TNase and SEA were demonstrable along the storage. Therefore, fermented milks may play an important role in the transmission of this organism.
Assuntos
Enterotoxinas/biossíntese , Lactobacillus/fisiologia , Leite/microbiologia , Staphylococcus aureus/crescimento & desenvolvimento , Streptococcus/fisiologia , Iogurte/microbiologia , Animais , Fermentação , Conservação de Alimentos , Concentração de Íons de Hidrogênio , Nuclease do Micrococo/análise , Intoxicação Alimentar Estafilocócica/transmissão , Staphylococcus aureus/metabolismo , Fatores de TempoRESUMO
Se inocularon 3 tipos de alimentos (embutidos cárnicos, pescados y leche) con diferentes concentraciones de cepas de Staphyloccoccus aureus (FRI-790 y FRI-S6), productoras de enterotoxinas estafilocócica y terminucleasa. Estas sustancias fueron extraídas y detectadas de los alimentos por métodos bioquímicos e inmunológicos. Todas las muestras dieron resultados positivos cuando el conteo de los microorganismos fuemayor menor que 10(6) ufc/g de alimento
Assuntos
Substitutos do Leite Humano/análise , Enterotoxinas/análise , Produtos Pesqueiros/análise , Amostras de Alimentos , Produtos da Carne/análise , Nuclease do Micrococo/análise , Staphylococcus aureus/isolamento & purificaçãoRESUMO
Demonstration of Staphylococcal Thermonuclease (TNase) from Powder Milk. Some authors have reported that the number of Staphylococcus aureus needed to produce a food-poisoning is 10(6) CFU per gram of food, however, other authors have reported foods without microorganisms but these have produced food-poisoning. Because the methods for staphylococcal enterotoxins demonstration in foods are laborious and expensive procedures, in this paper we tried to demonstrate the thermonuclease (TNase) presence in foods directly, as a helper test for screening foods suspected to be contaminated with this microorganism. To 112 powder milk samples were determined TNase presence by Tatini's et al (1976) and Lachica's (1972) technics, 31 of this samples had S. aureus. Only with Lachica's technique it could be possible to demonstrate TNase in 17 of 112 analyzed samples, 14 of these had viable S. aureus.
Assuntos
Proteínas de Bactérias/análise , Laticínios/microbiologia , Microbiologia de Alimentos , Nuclease do Micrococo/análise , Leite/microbiologia , Staphylococcus aureus/isolamento & purificação , Animais , Biomarcadores , Sensibilidade e EspecificidadeRESUMO
The efficiency of Baird-Parker agar, mannitol-salt agar, Vogel-Johnson agar and Giolitti-Cantoni broth for the detection of Staphylococcus aureus from food samples, was studied by comparing the numbers of Staphylococcus recovered from the samples, the degree of selectivity reached and the recovery of coagulase and thermonuclease positive staphylococci. Lowest counts of Staphylococcus were obtained with Giolitti-Cantoni broth. The mannitol-salt agar proved to be the most efficient media system with respect to the number of staphylococci recovered and the degree of selectivity reached. None of these media was highly selective for the isolation and detection of S. aureus; therefore, it is necessary to identify the isolated colonies in all cited media, in order to use rightly the current guidelines for microbiological quality of foods.