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- Listeria monocytogenes: biofilm formation abilityPublication . Barbosa, J.; Carvalheira, A.; Gibbs, P.; Teixeira, P.
- 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.
- Diverse geno- and phenotypes of persistent listeria monocytogenes isolates from fermented meat sausage production facilities in PortugalPublication . Ferreira, V.; Barbosa, J.; Stasiewicz, M.; Vongkamjan, K.; Switt, A. Moreno; Hogg, T.; Gibbs, P.; Teixeira, P.; Wiedmann, M.The persistence of Listeria monocytogenes in food-associated environments represents a key factor in transmission of this pathogen. To identify persistent and transient strains associated with production of fermented meat sausages in northern Portugal, 1,723 L. monocytogenes isolates from raw material and finished products from 11 processors were initially characterized by random amplification of polymorphic DNA (RAPD), PCR-based molecular serotyping, and epidemic clone characterization, as well as cadmium, arsenic, and tetracycline resistance typing. Pulsed-field gel electrophoresis (PFGE) typing of 240 representative isolates provided evidence for persistence of L. monocytogenes for periods of time ranging from 10 to 32 months for all seven processors for which isolates from different production dates were available. Among 50 L. monocytogenes isolates that included one representative for each PFGE pattern obtained from a given sample, 12 isolates showed reduced invasion efficiency in Caco-2 cells, including 8 isolates with premature stop codons in inlA. Among 41 isolates representing sporadic and persistent PFGE types, 22 isolates represented lysogens. Neither strains with reduced invasion nor lysogens were overrepresented among persistent isolates. While the susceptibility of isolates to lysogenic phages also did not correlate with persistence, it appeared to be associated with molecular serotype. Our data show the following. (i) RAPD may not be suitable for analysis of large sets of L. monocytogenes isolates. (ii) While a large diversity of L. monocytogenes subtypes is found in Portuguese fermented meat sausages, persistence of L. monocytogenes in this food chain is common. (iii) Persistent L. monocytogenes strains are diverse and do not appear to be characterized by unique genetic or phenotypic characteristics.
- 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.
- Listeriosis: is it a problem?Publication . Silva, J.; Teixeira, P.; Barbosa, J.; Almeida, G.; Santos, I.; Magalhães, R.
- Microbiological contamination of reusable plastic bags for food transportationPublication . Barbosa, J.; Albano, H.; Silva, C. P.; Teixeira, P.Nowadays, with so many concerns for the environment, the use of reusable plastic bags is becoming routine, instead of the use of polluting single-use plastic bags. However, this is controversial in terms of food safety, since consumers transport many different foods, which could contaminate their bags and pose a risk to their health due to cross-contamination. This study aimed to detect or enumerate several indicators/pathogens from 30 used reusable plastic (polypropylene) bags and, to evaluate their antibiotic resistance profiles after identification by 16s rRNA of each isolated microorganism. Several genera of Enterobacteriaceae, coagulase-negative staphylococci and also Listeria monocytogenes were found in the reusable plastic bags analyzed. In general, high percentages of antibiotics resistance were found, highlighting the elevated occurrence of multi-resistant isolates of coagulase-negative staphylococci and Enterobacteriaceae. This study demonstrates the level and variety of microbial contamination of some used reusable plastic bags. No correlation was found between microbial levels and the visual appearance of each bag demonstrating that appearance is not a reliable datum about the bag contamination. We believe that this study could help the competent authorities taking measures to alert consumers to good food safety practices, not only in their kitchens, but also in the bags that carry their food.
- Differences between clinical and food isolates of Listeria monocytogenes in biofilm formationPublication . Barbosa, J.; Silva, J.; 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.
- Influence of sub-lethal stresses on the survival of lactic acid bacteria after spray-drying in orange juicePublication . Barbosa, J.; Borges, S.; Teixeira, P.The demand for new functional non-dairy based products makes the production of a probiotic orange juice powder an encouraging challenge. However, during drying process and storage, loss of viability of the dried probiotic cultures can occur, since the cells are exposed to various stresses. The influence of sub-lethal conditions of temperature, acidic pH and hydrogen peroxide on the viability of Pediococcus acidilactici HA-6111-2 and Lactobacillus plantarum 299v during spray drying in orange juice and subsequent storage under different conditions was investigated. At the end of storage, the survival of both microorganisms through simulated gastro-intestinal tract (GIT) conditions was also determined. The viability of cells previously exposed to each stress was not affected by the drying process. However, during 180 days of storage at room temperature, unlike P. acidilactici HA-6111-2, survival of L. plantarum 299v was enhanced by prior exposure to sub-lethal conditions. Previous exposure to sub-lethal stresses of each microorganism did not improve their viability after passage through simulated GIT. Nevertheless, as cellular inactivation during 180 days of storage was low, both microorganisms were present in numbers of ca. 10(7) cfu/mL at the end of GIT. This is an indication that both bacteria are good candidates for use in the development of an orange juice powder with functional characteristics.
- Virulence factors among enterococci isolated from traditional fermented meat products produced in the North of PortugalPublication . Barbosa, J.; Gibbs, P.A.; Teixeira, P.The aim of this work was to characterize Enterococcus spp. isolated from Alheira, Chouriça de Vinhais and Salpicão de Vinhais, fermented meat products produced in the North of Portugal, concerning their potential pathogenicity. One hundred and eighty two isolates (76 identified as Enterococcus faecalis, 44 as Enterococcus faecium, 1 as Enterococcus casseliflavus and 61 as Enterococcus spp.) were studied. Twenty six percent of isolates were gelatinase producers. None of the isolates produced lipase nor DNase activities. Hemolytic activity using sheep and human blood from two types (A and O) was assessed. One isolate was b-hemolytic in human blood. Results obtained in sheep blood were quite different from those obtained in human blood. Biofilm production in batch and in fed-batch mode was evaluated. In batch mode, only 28.0% and 3.9% of isolates were classified as moderate and strong biofilm producers, respectively, and in fed-batch mode, 35.7% and 63.2% of isolates were classified as moderate and strong biofilm producers, respectively. The presence of 13 virulence genes (efaAfs, efaAfm, esp, agg, cylM, cylB, cylA, cylLL cylLs and gelE) were investigated by PCR. The majority of enterococcal isolates showed the presence of one or more virulence factors, the most frequent genotype being efaAfs+ gelE+ agg+ (41.5%). E. faecalis isolates harbored multiple virulence traits, while E. faecium isolates were generally free of virulence determinants. Phenotypic and genotypic evidence of potential virulence factors were identified in Enterococcus spp. isolates, which is a reason of concern.