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- Genotypic and phenotypic characterization of staphylococcus aureus in children from Northern PortugalPublication . Silva, J.; Smicht, H.; Lopo, N.; Castro, A.; Teixeira, P.
- Effects of addition of sucrose and salt, and of starvation upon thermotolerance and survival during storage of freeze-dried Lactobacillus delbrueckii ssp bulgaricusPublication . Carvalho, A. S.; Silva, J.; Ho, P.; Teixeira, P.; Malcata, F. X.; Gibbs, P.Increased survival of freeze-dried cells of Lactobacillus bulgaricus was observed when the drying medium was supplemented with sucrose; however, the magnitude of such protection was dependent on the growth medium used. Supplementing the growth medium with NaCl markedly increased survival of dried cells, and only a small effect was exerted by the composition of the drying medium or prior to starvation of cells. The D57 values of Lactobacillus bulgaricus cells grown in MRS were about half of those of cells grown in MRS supplemented with sucrose, with sucrose plus NaCl, or with NaCl.
- Effect of various growth media upon survival during storage of freeze-dried Enterococcus faecalis and Enterococcus duransPublication . Carvalho, A.S.; Silva, J.; Ho, P.; Teixeira, P.; Malcata, F. X.; Gibbs, P.The effects of three different growth media (MRS, M17 and Lee’s) on survival during freeze-drying and subsequent storage of six strains of Enterococcus faecalis and two strains of E. durans were investigated. Methods and Results: Distinct Enterococcus spp. strains were grown on M17, MRS and Lee’s broth, freeze-dried and stored at 20 C in air under darkness. At regular intervals throughout storage, freeze-dried samples were rehydrated and then plated on M17 agar. Conclusions: A higher survival rate during storage of dried E. durans was obtained when growth occurred in MRS. The same effect was not observed, however, for the majority of E. faecalis strains, which clearly survived better in the dried state when this organism had been grown in M17 or Lee’s medium. Significance and Impact of Study: The survival of the dried Enterococcus spp. tested during storage was shown to be strain-specific and dependent on the growth medium.
- A functional dried fruit matrix incorporated with probiotic strains: Lactobacillus Plantarum and Lactobacillus KefirPublication . Rêgo, A.; Freixo, R.; Silva, J.; Gibbs, P.; Morais, A. M. M. B.; Teixeira, P.The consumption of probiotic functional foods, i.e. processed foods enriched with microorganisms that confer health benefits to the host, shows a progressive increase in the last decade due to changes in habits and trends of consumers attracted by the benefits of these products. Currently, the development of fruits and vegetables with probiotic content is a topic of high interest for the probiotic-food consumers as these are a popular item perceived as healthy by consumers, and issues related with lactose intolerance are overcome. The aim of this research study was to develop a new healthy dry food that contains a source of probiotic strains providing some benefits to consumers. Apple was selected as an experimental food matrix and two different probiotic Lactobacillus species, L. plantarum and L. kefir, were tested separately. Samples were taken immediately before and after the drying process in order to determine the viability of bacteria adhered to the matrix. Dried apple cubes were stored in sterile closed glass containers or in sealed bags vacuum packed and normal atmosphere) at room temperature and at 4ºC. The bacterial viability in the dried product was tested at different storage times. For both probiotic strains, a decrease of approximately 2 log cycles in bacterial cell numbers was observed after drying. The bacterial number in apple cubes at the time of storage at room temperature and 4ºC was approximately 1x107 cfu/g. Both probiotic strains died after one month of storage at room temperature, while during storage at 4ºC the cells remained viable after 3 months, with bacterial number around 1x106 cfu/g.
- Clinical isolates of L. monocytogenes: serotyping, biotyping and susceptibility to antibioticsPublication . Almeida, G.; Ferreira, V.; Magalhães, R.; Barbosa, J.; Silva, J.; Teixeira, P.; Hogg, T.
- Evaluation of the hippurate test as a method for the differentiation between Campylobacter jejuni and Campylobacter coliPublication . Mena, C.; Leite, D.; Silva, J.; Gibbs, P.; Teixeira, P.
- Behavior of Listeria monocytogenes isolates through gastro-intestinal tract passage simulation, before and after two sub-lethal stressesPublication . Barbosa, J.; Borges, S.; Magalhães, R.; Ferreira, V.; Santos, I.; Silva, J.; Almeida, G.; Gibbs, P.; Teixeira, P.The effects of previous exposure to sub-lethal acidic and osmotic stresses on the survival of Listeria monocytogenes during exposure to gastro-intestinal (GI) tract simulation, was investigated. Six L. monocytogenes strains isolated from cheeses were selected and exposed to high salt concentrations or acidic conditions and their viability compared in quick and slow digestions. The results demonstrated that (i) all isolates were more sensitive to the exposure to acidic than to osmotic sub-lethal conditions (ii) significant differences (p < 0.05) between the two types of digestion were observed; in slow digestion, the log reduction was higher for all the tested isolates (iii) all isolates were inhibited in the presence of bile salts for both types of digestion (iv) differences between quick and slow digestion were not observed (p > 0.05) after exposure to either osmotic or acidic stress (v) a higher cellular inactivation (p < 0.001) was observed during the passage through the GI tract simulation after exposure to osmotic than to acidic stresses and (vi) neither osmotic nor acidic sub-lethal stresses conferred resistance to simulated GI tract conditions.
- Bacteriocin production by spray-dried lactic acid bacteriaPublication . Silva, J.; Carvalho, A.S.; Teixeira, P.; Gibbs, P.A.Cell survival and antagonistic activity against Listeria innocua, Listeria monocytogenes and Staphylococcus aureus were investigated after spray-drying three bacteriocin-producing strains of lactic acid bacteria: Carnobacterium divergens, Lactobacillus salivarius and Lactobacillus sakei.
- Listeriosis: is it a problem?Publication . Silva, J.; Teixeira, P.; Barbosa, J.; Almeida, G.; Santos, I.; Magalhães, R.
- Genotypic and phenotypic characterization of staphylococcus aureus in children from Northern PortugalPublication . Silva, J.; Smicht, H.; Lopo, N.; Castro, A.; Teixeira, P.