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- 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.
- Epidemiological data on listeriosis in Portugal: 2003 – 2008Publication . Almeida, G.; Magalhães, R.; Hogg, T.; 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.
- Persistence of L. monocytogenes in artisanal cheese producing plantsPublication . Almeida, G.; Santos, I.; Magalhães, R.; Joana, B.; Hogg, T.; Teixeira, P.
- Listeriosis: is it a problem?Publication . Silva, J.; Teixeira, P.; Barbosa, J.; Almeida, G.; Santos, I.; Magalhães, R.
- Enterobacter sakazakii and other pathogens in powdered infant formula (PIF)Publication . Magalhães, R.; Almeida, G.; Teixeira, P.
- Characterization of Listeria monocytogenes isolated from human cases of listeriosis occurred in Portugal in 2008Publication . Magalhães, R.; Almeida, G.; Teixeira, P.
- Listeria: is it a problem?Publication . Barbosa, J.; Ferreira, V.; Albano, H.; Magalhães, R.; Santos, I.; Castro, A.; Silva, J.; Almeida, G.; Teixeira, P.
- Distribution and characterization of Listeria monocytogenes clinical isolates in Portugal, 1994–2007Publication . Almeida, G.; Morvan, A.; Magalhães, R.; Santos, I.; Hogg, T.; Leclercq, A.; Teixeira, P.In recent years, the number of cases of listeriosis has increased worldwide. Ninety-five isolates of Listeria monocytogenes recovered from Portuguese human cases of listeriosis have been characterized by biotyping (cadmium and arsenic sensitivity), polymerase chain reaction (PCR) grouping, and by pulsed-field gel electrophoresis (PFGE) applying the enzymes AscI and ApaI. Isolates were classified into one of three PCR groups; IVb (71.6%), IIb (17.9%), and IIa (10.5%). Four biotypes were differentiated: sensitive to arsenic/cadmium (48.4%), arsenic-sensitive and cadmium-resistant (25.3%), resistant to arsenic and sensitive to cadmium (18.9%), and resistant to both heavy metals (7.4%). Combined analyses of AscI and ApaI patterns yielded a total of 58 PFGE types with five sets (G, Jb, KKa, Me, and U) of Portuguese strains, each of which were indistinguishable by PFGE typing. In the present study, it was demonstrated that there are recurrent pulsotypes and that some were the same pulsotypes linked to outbreaks in France. In addition, there are some pulsotypes spread throughout the country, while others only appear in a restricted region. This study allowed the assembly of a first large pulsotype database of Portuguese clinical strains.
- Occurence of Listeria monocytogenes in food products collected in Portugal from retail establishments and food plantsPublication . Mena, C.; Carneiro, L.; Silva, I.; Magalhães, R.; Almeida, G.; Teixeira, P.