CHARACTERISTICS OF SPECIFIC STRAINS OF LISTERIA MONOCYTOGENES POTENTIATING PERSISTENCE IN FOOD AND FOOD PROCESSING ENVIRONMENTS AND RELEVANCE TO FOOD SAFETY

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Characterization of clinical and food Listeria monocytogenes isolates with different antibiotic resistance patterns through simulated gastrointestinal tract conditions and environmental stresses

Publication . Cunha, S.; Komora, N.; Magalhães, R.; Almeida, Gonçalo; Ferreira, V.; Teixeira, Paula

Thirty-three Listeria monocytogenes isolates previously collected from two sources, food (n = 18) and human patients suffering from listeriosis (n = 15), with variable antibiotic susceptibility profiles (sensitive/resistant) to erythromycin, ciprofloxacin and nitrofurantoin, were studied for their ability to survive (i) the environmental stress provided by sequential conditions that simulate the digestive tract, and (ii) extreme pH values (1.5–12). The results showed a response that was only strain dependent. There were no variability in survival results based on type of stress (low or high pH), source (food or clinical), or sensitivity/resistance to antibiotics (p > 0.01). Some strains of L. monocytogenes are able to survive extreme acid and alkaline conditions, and conditions that mimic the sequential stressors found in the gastro-intestinal tract. The resistance to the antibiotics tested in this study by some L. monocytogenes strains did not confer any cross-protection to acid or alkaline stressors.

2016Journal article

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Presence of microbial pathogens and genetic diversity of listeria monocytogenes in a constructed wetland system

Publication . Calheiros, Cristina S. C.; Ferreira, Vânia; Magalhães, Rui; Teixeira, Paula; Castro, Paula

The potential of constructed wetlands (CWs) as a low technology for wastewater treatment is timely but there is a need to understand the route of pathogenic bacteria (Listeria monocytogenes and Salmonella spp.) and indicator organisms (Enterobacteriaceae and Escherichia coli) present in wastewater within those systems and to what extent they can compromise the further use of the plants (enabling in-house ornamental use) and water reuse (irrigation purposes). In the present study the fate of potential pathogenic bacteria within a CW, with ornamental plants, and an outlet pond established in a tourism house for wastewater treatment was assessed. The fate of pathogenic bacteria in lettuce, both plant tissues and soil, subject to irrigation with water contaminated either with L. monocytogenes or E. coli (indicator organism) was investigated. The uptake of indicator organisms by the CW ornamental plants was low and there was a decrease, from the CW wastewater inlet to the outlet, of up to 3 log for Enterobacteriaceae and up to 2 log for E. coli. Concerning Salmonella spp. no detection was registered in the water, plant tissues or substrate within the CW. On the other hand, several L. monocytogenes isolates were retrieved from water, root and substrate samples, found to have a high susceptibility to a battery of antibiotics. The irrigation of lettuce with water containing pathogenic bacteria (L. monocytogenes) and indicator organisms (E. coli) must be considered with caution since both bacteria were detected in the soil growing media and internalization of L. monocytogenes in roots was observed. These issues are poorly investigated and to our knowledge not addressed in the sphere of CWs.

2017Journal article

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Biofilm formation by persistent and non-persistent listeria monocytogenes strains on abiotic surfaces

Publication . Magalhães, R.; Ferreira, V.; Biscottini, G.; Brandão, T. R. S.; Almeida, G.; Teixeira, Paula

Contaminated 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.

2017Journal article

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Publication . Magalhães, R.; Almeida, G.; Ferreira, V.; Santos, I.; Silva, J.; Mendes, M. M.; Pita, J.; Mariano, G.; Mâncio, I.; Sousa, M. M.; Farber, J.; Pagotto, F:; Teixeira, P.

In Portugal, listeriosis has been notifiable since April 2014, but there is no active surveillance programme for the disease. A retrospective study involving 25 national hospitals led to the detection of an outbreak that occurred between March 2009 and February 2012. The amount of time between the start of the outbreak and its detection was 16 months. Of the 30 cases of listeriosis reported, 27 were in the Lisbon and Vale do Tejo region. Two cases were maternal/neonatal infections and one resulted in fetal loss. The mean age of the non-maternal/neonatal cases was 59 years (standard deviation: 17); 13 cases were more than 65 years-old. The case fatality rate was 36.7%. All cases were caused by molecular serogroup IVb isolates indistinguishable by pulsed-field gel electrophoresis and ribotype profiles. Collaborative investigations with the national health and food safety authorities identified cheese as the probable source of infection, traced to a processing plant. The magnitude of this outbreak, the first reported food-borne listeriosis outbreak in Portugal, highlights the importance of having an effective listeriosis surveillance system in place for early detection and resolution of outbreaks, as well as the need for a process for the prompt submission of Listeria monocytogenes isolates for routine laboratory typing.

2015Journal article

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Genome sequence of listeria monocytogenes 2542, a serotype 4b strain from a cheese-related outbreak in Portugal

Publication . Ferreira, Vânia; Magalhães, Rui; Almeida, Gonçalo; Cabanes, Didier; Fritzenwanker, Moritz; Chakraborty, Trinad; Hain, Torsten; Teixeira, Paula

We report here the draft genome sequence of Listeria monocytogenes 2542, a serotype 4b clinical strain recovered from a placental sample during a cheese-related listeriosis outbreak in Portugal.

2018Journal article

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