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Listeria monocytogenes persistence in food associated environments: epidemiology, strain characteristics, and implications for public health

Publication . Ferreira, V.; Wiedmann, M.; Teixeira, P.; Stasiewicz, M. J.

Over the last 10 to 15 years, increasing evidence suggests that persistence of Listeria monocytogenes in food processing plants for years or even decades is an important factor in the transmission of this foodborne pathogen and the root cause of a number of human listeriosis outbreaks. L. monocytogenes persistence in other food-associated environments (e.g., farms and retail establishments) may also contribute to food contamination and transmission of the pathogen to humans. Although L. monocytogenes persistence is typically identified through isolation of a specific molecular subtype from samples collected in a given environment over time, formal (statistical) criteria for identification of persistence are undefined. Environmental factors (e.g., facilities and equipment that are difficult to clean) have been identified as key contributors to persistence; however, the mechanisms are less well understood. Although some researchers have reported that persistent strains possess specific characteristics that may facilitate persistence (e.g., biofilm formation and better adaptation to stress conditions), other researchers have not found significant differences between persistent and nonpersistent strains in the phenotypic characteristics that might facilitate persistence. This review includes a discussion of our current knowledge concerning some key issues associated with the persistence of L. monocytogenes, with special focus on (i) persistence in food processing plants and other food-associated environments, (ii) persistence in the general environment, (iii) phenotypic and genetic characteristics of persistent strains, (iv) niches, and (v) public health and economic implications of persistence. Although the available data clearly indicate that L. monocytogenes persistence at various stages of the food chain contributes to contamination of finished products, continued efforts to quantitatively integrate data on L. monocytogenes persistence (e.g., meta-analysis or quantitative microbial risk assessment) will be needed to advance our understanding of persistence of this pathogen and its economic and public health impacts.

2014Journal article

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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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Detection of premature stop codons leading to truncated internalin A among food and clinical strains of Listeria monocytogenes

Publication . Silva, Margarida Ferreira da; Ferreira, Vânia; Magalhães, Rui; Almeida, Gonçalo; Alves, Artur; Teixeira, Paula

Listeria monocytogenes is a food-borne pathogen responsible for outbreaks and sporadic cases of listeriosis, a severe invasive disease. Internalin A (InlA) a protein encoded by inlA has a key role in the mechanism of pathogenesis in L. monocytogenes infection, specifically in the invasion of human intestinal epithelial cells. Studies on inlA have shown that mutations leading to premature stop codons (PMSCs) occur naturally and are associated with impaired virulence of L. monocytogenes strains. Increasing evidence suggests that inlA PMSCs mutations are frequent in strains from foods, but rare among clinical isolates. In this study, 22 L. monocytogenes strains collected in Portugal from the processing environment of a bakery industry (n = 1), different food products (n = 10) and human clinical cases (n = 11) were analysed for mutations in inlA and invasion efficiency in Caco-2 cells. Sequencing revealed previously reported mutations types leading to PMSCs in three food and one clinical strain presenting different molecular serotypes (i.e., IIa, IIb and IIc). The remaining 18 isolates did not show PMSCs in inlA. The four strains with PMSCs in inlA presented lower invasiveness efficiencies in Caco-2 cells (below 8.9%) when compared to the control strain (full-length InlA). In addition, one clinical isolate showed reduced invasion efficiency but no PMSCs in inlA. This isolate showed increased inlA transcript levels to that obtained for the laboratory control strain. Our data support the hypothesis that L. monocytogenes isolated from food have attenuated invasion due to the presence of inlA PMSCs. This information would be critically needed for adequate risk-assessments of the foodborne illness burden associated with L. monocytogenes strains.

2017Journal article

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High hydrostatic pressure effects on Listeria monocytogenes and L. innocua: evidence for variability in inactivation behaviour and in resistance to pediocin bacHA-6111-2

Publication . Bruschi, Carolina; Komora, Norton; Castro, Sónia Marília; Saraiva, Jorge; Ferreira, Vânia Borges; Teixeira, Paula

The effect of high hydrostatic pressure (HHP) on the survival of 14 strains of Listeria monocytogenes from food or clinical origins, selected to represent different pheno and genotypes, was evaluated. Stationary phase cells were submitted to 300, 400 and 500 MPa at 10 °C, for 5 min. A high variability in the resistance of L. monocytogenes to pressure was observed, and particularly two strains isolated from food were significantly more baroresistant than the rest. Strains of L. monocytogenes resistant to one or more antibiotics exhibited significantly higher levels of survival after the high pressure treatment at 400 MPa. No correlation was found between strains' origin or thermal tolerance and resistance to HHP. The suitability of two strains of L. innocua as surrogates of L. monocytogenes, was also investigated. These exhibited significantly higher sensitivities to HHP than observed for some L. monocytogenes. The antimicrobial effect of the antilisterial bacteriocin (bacHA-6111-2) increased after L. monocytogenes cells had been exposed to pressure. The data obtained underlines the importance of strain selection for studies aiming to evaluate HHP efficacy to ensure safety of HHP-treated foods.

2017Journal 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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