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- Virulence genes amongst strains of L. monocytogenes isolated from cheesesPublication . Almeida, Gonçalo; Teixeira, Paula; Hogg, Tim
- Evaluation of antibiotic resistance patterns of food and clinical Listeria monocytogenes isolates in PortugalPublication . Barbosa, Joana; Magalhães, Rui; Santos, Isabel; Ferreira, Vânia; Brandão, Teresa R. S.; Silva, Joana; Almeida, Gonçalo; Teixeira, PaulaThe aim of this study was to characterize a broad collection of isolates of Listeria monocytogenes, of different serotypes, recovered in Portugal between 2003 and 2007 from foods (n = 353) and from clinical cases of human listeriosis (n = 95), in terms of antimicrobial susceptibility. All the isolates were susceptible to ampicillin, the preferred agent to treat listeriosis. Resistances to nitrofurantoin (n = 99), to ciprofloxacin (n = 18), to erythromycin (n = 10), to tetracycline (n = 2), to gentamicin (n = 1) and to rifampicin (n = 1) were observed. One hundred (28.3%) and 20 (21.0%) food and clinical isolates, respectively, were resistant to at least one antibiotic. Eight isolates (1.8%) were resistant to two or more antimicrobials of different classes, and all were collected from foods. Serogroup IVb included the highest percentage of isolates resistant to erythromycin. The highest percentages of isolates resistant to nitrofurantoin were of serogroup IVb and IIc. It was demonstrated that the incidence of antibiotic-resistant isolates of L. monocytogenes, during the period 2003 to 2007, was low in Portugal but still higher than that observed in other countries. Given the increasing population at greater risk of listeriosis, namely, the elderly, the high mortality rate of the infection and the detection of resistant isolates, monitoring for antibiotic resistance in strains of L. monocytogenes on a large scale, and assessing the risk of infection by these strains, is highly recommended.
- First confirmed human outbreak of Listeria monocytogenes in PortugalPublication . Almeida, G.; Magalhães, R.; Santos, I.; Ferreira, V.; Silva, J.; Mendes, M. M.; Nabais, P.; Fernandes, M. G. Mariano; Mâncio, M. I.; Sousa, M. M.; Teixeira, Paula
- Listeria monocytogenes in cheese: occurrence, sources of contamination, control, risks to public healthPublication . Almeida, Gonçalo N.; Hogg, Tim; Teixeira, Paula
- Pesquisa de Listeria monocytogenes em produtos cárneos fumados e de salsichariaPublication . Vaz-Velho, Manuela; Almeida, Gonçalo; Mena, Cristina; Carneiro, Luisa; Freitas, António
- Biofilm formation by persistent and non-persistent listeria monocytogenes strains on abiotic surfacesPublication . Magalhães, R.; Ferreira, V.; Biscottini, G.; Brandão, T. R. S.; Almeida, G.; Teixeira, PaulaContaminated food with Listeria monocytogenes is the predominant route of transmission of listeriosis to humans, a severe illness with a high mortality rate. Food processing environments can be colonized by persistent strains, repeatedly isolated for months or years. This study aimed to investigate the biofilm formation capacity of six strains of L. monocytogenes that persisted for long periods in two cheese processing plants in comparison to seven strains isolated sporadically from the same plants. Persistent strains produced more biofilm than non-persistent strains on stainless steel and silicon rubber surfaces; no significant differences were observed on polyvinyl chloride (PVC). In a polystyrene microtiter plate assay with crystal violet staining, no evidence was found that persistent strains have higher ability to form biofilm than non-persistent strains, and no correlation was identified between biofilm formation in the microtiter plate and on the three other surfaces tested.
- Pesquisa de Listeria monocytogenes em produtos cárneos fumados e de salsichariaPublication . Almeida, Gonçalo; Mena, Cristina; Carneiro, Luisa
- Study of Biological Hazards Present on the Surfaces of Selected Fruits and VegetablesPublication . Noronha, Lúcia; Castro, Ana; Ferreira, Vânia; Magalhães, Rui; Almeida, Gonçalo; Mena, Cristina; Silva, Joana; Teixeira, PaulaThis study evaluated the microbial load on the surface of fruits with rough and very pronounced textured peels, namely pineapples and melons (cantaloupe), and investigated the presence of foodborne pathogens in these products since they are usually eaten raw. Similarly, lettuce is one of the most common salad vegetables consumed raw in Portugal, it therefore being important to study the microbial status of lettuce leaves. Enumerations of aerobic mesophilic counts, Enterobacteriaceae, Escherichia coli and coagulase-positive staphylococci, as well as detection of Listeria monocytogenes and Salmonella spp., were performed for all samples. Only in melon samples were E. coli and coagulase-positive staphylococci not detected. Contamination with L. monocytogenes varied from 2.5% and 15% in pineapple/melon and lettuce samples, respectively. Salmonella spp. were not detected. All coagulase-positive staphylococci had similar characteristics and none exhibited multidrug resistance. L. monocytogenes isolates belonged to serogroups II (1/2c or 3c), or to serogroup IV (4b, 4d and 4e). None were found to be resistant to antibiotics commonly used in therapy of listeriosis.
- Food Safety in the domestic environment: incidence of Listeria monocytogenes in domestic refrigeratorsPublication . Marujo, Daniela; Pereira, Isabel; Mena, Cristina; Carneiro, Luísa; Almeida, Gonçalo; Teixeira, Paula; Gibbs, Paul
- Incidence of Listeria spp. in domestic refrigerators in PortugalPublication . Azevedo, Inês; Regalo, Mafalda; Mena, Cristina; Almeida, Gonçalo; Carneiro, Luísa; Teixeira, Paula; Hogg, Tim; Gibbs, Paul A.The main objectives of this study were to determine the incidence of Listeria spp. in Portuguese domestic refrigerators and to evaluate some of the hygienic practices in the domestic environment that might contribute to the persistence of the organisms. It was found that L. monocytogenes was present in 3 domestic refrigerators of the 86 investigated. L. grayi and L. innocua were also isolated from 4 and 1 refrigerators, respectively. Overall, the information obtained from our survey demonstrates the need for consumer education in Portugal regarding safe food handling practices. For the refrigerators investigated, ≈71% were operating at a temperature higher than 6.1ºC, 87% were cleaned only monthly or less frequently, and only 8% were cleaned with appropriate proprietary cleaning products available in supermarkets.