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Behavior of Listeria monocytogenes isolates through gastro-intestinal tract passage simulation, before and after two sub-lethal stresses

Publication . 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.

2012Journal article

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Survival of clinical and food isolates of listeria monocytogenes through simulated gastrointestinal tract conditions

Publication . Ramalheira, Rosário; Almeida, Marta; Azeredo, Joana; Brandão, Teresa R.S.; Almeida, Gonçalo; Silva, Joana; Teixeira, Paula

Twenty-seven strains of Listeria monocytogenes previously isolated from food (n¼16) and human patients of listeriosis (n¼11) were characterized and compared based on their ability to survive through the simulated gastrointestinal tract conditions. Cells were exposed (60 or 120 min) to low pH in the presence of pepsin, to simulate the digestion in the stomach, and subsequently to bile salts to simulate the digestion in the small intestine (60 or 120 min). Their survival was shown to be origin- (food and clinical) and strain dependent ( p<0.001) and also significantly dependent on the imposed simulated gastric conditions (long vs. quick exposure) ( p<0.001). In comparison to the food isolates, the clinical strains were in general more resistant and survived better to the two challenges imposed. Some of the tested strains, after the exposure to low pH in the presence of pepsin, became injured and subsequently more susceptible to the bile salts challenge. It was demonstrated that one of the most important natural barriers against foodborne pathogens might not be effective since it was shown that L. monocytogenes isolates that survived through the pH challenge were also able to survive the subsequent challenge to bile salts.

2010Journal article

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Influence of Listeria innocua on the growth of Listeria monocytogenes

Publication . Carvalheira, Ana; Eusébio, Cátia; Silva, Joana; Gibbs, Paul; Teixeira, Paula

The growth of Listeria monocytogenes and Listeria innocua strains was monitored during this study: (i) in TSB–YE media and (ii) in a food matrix (pasteurized milk) according to the ISO 11290-1 methodology. Different inocula concentrations and mixtures were tested. The response was shown to be strain dependent. In TSB–YE the inhibition of a L. monocytogenes strain was observed in just one of the three mixtures (L. monocytogenes_1340 with L. innocua_11288) showing a reduction of 1.37 log cfu/ml after 42.5 h and 1.85 log after 66.5 h of incubation. In pasteurized milk the inhibition of L. monocytogenes by L. innocua was always observed when L. innocua was present in higher concentrations than L. monocytogenes. The reverse was also observed but only in one mixture (cocktail of six L. monocytogenes with L. innocua_ 2030c) when the initial concentration of L. monocytogenes was 100 times higher than L. innocua suggesting the phenomenon of quorum sensing. Furthermore, inhibitory activity was not caused by bacteriocins, and no correlation between the growth rate and inhibition was demonstrated.

2010Journal article

Open access

Diverse geno- and phenotypes of persistent listeria monocytogenes isolates from fermented meat sausage production facilities in Portugal

Publication . 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.

2011Journal article

Open access

Distribution and characterization of Listeria monocytogenes clinical isolates in Portugal, 1994–2007

Publication . 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.

2010Journal article

Open access