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Concept: Listeriosis

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Listeria monocytogenes infection is most commonly recognized in ruminants, including cattle, sheep, and goats; but it is rarely diagnosed in poultry. This report describes an outbreak of L. monocytogenes in a backyard poultry flock. Also, it points out the importance of collaboration between veterinarians and public health departments and the possible implications of zoonotic diseases.

Concepts: Epidemiology, Listeria monocytogenes, Listeria, Listeriosis, Livestock, Goat, Joseph Lister, 1st Baron Lister, Herbivorous animals

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The objective of this study was to evaluate the susceptibility of 259 Listeria monocytogenes strains isolated from food and food-processing environments and patient samples in Germany to 14 antibiotics widely used in veterinary and human medicine. L. monocytogenes strains were isolated mainly from milk and milk products and classified according to their molecular serotypes IIa (n=112), IIb (n=41), IIc (n=36), IVa (n=1), IVb (n=66), and IVb-v1 (n=3).

Concepts: Medicine, Microbiology, Fungus, Antibiotic, Listeria monocytogenes, Listeria, Listeriosis, Joseph Lister, 1st Baron Lister

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Listeria monocytogenes can asymptomatically inhabit the human intestine as a commensal bacterium. However, the mechanism by which L. monocytogenes is able to inhabit the intestine without pathogenic symptoms remains unclear. Here, we compared the invasion efficiency of L. monocytogenes strains with the 268- and 385-bp-long actA gene. Clinical strains SMFM-CI-3 and SMFM-CI-6 with 268-bp actA isolated from patients with listeriosis and strains SMFM-SI-1 and SMFM-SI-2 with the 385-bp gene isolated from carcasses were used for inoculum preparation. The invasion efficiency of these strains was evaluated using Caco-2 cells (intestinal epithelial cell line), prepared as normal and healthy cells with tightened tight junctions and senescent cells with loose tight junctions, which were loosened by adriamycin treatment. The invasion efficiency of L. monocytogenes strains with the 268-bp-long actA gene was 1.12.6-times lower than that of the strains with the 385-bp-long gene in normal and healthy cells. However, the invasion efficiency of both types of strains did not differ in senescent cells. Thus, L. monocytogenes strains with the 268-bp-long actA gene can inhabit the intestine asymptomatically as a commensal bacterium, but they may invade the intestinal epithelial cells and cause listeriosis in senescent cells.

Concepts: Bacteria, Epithelium, Intestine, Meningitis, Listeria monocytogenes, Listeria, Listeriosis, Intestinal epithelium

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A 2014 multistate listeriosis outbreak was linked to consumption of caramel-coated apples, an unexpected and previously unreported vehicle for Listeria monocytogenes. This outbreak was unanticipated because both the pH of apples (<4.0) and the water activity of the caramel coating (<0.80) are too low to support Listeria growth. In this study, Granny Smith apples were inoculated with approximately 4 log10 CFU of L. monocytogenes (a cocktail of serotype 4b strains associated with the outbreak) on each apple's skin, stem, and calyx. Half of the apples had sticks inserted into the core, while the remaining apples were left intact. Apples were dipped into hot caramel and stored at either 7°C or 25°C for up to 11 or 28 days, respectively. Data revealed that apples with inserted sticks supported significantly more L. monocytogenes growth than apples without sticks under both storage conditions. Within 3 days at 25°C, L. monocytogenes populations increased >3 log10 in apples with sticks, whereas only a 1-log10 increase was observed even after 1 week for caramel-coated apples without sticks. When stored at 7°C, apples with sticks exhibited an approximately 1.5-log10 increase in L. monocytogenes levels at 28 days, whereas no growth was observed in apples without sticks. We infer that insertion of a stick into the apple accelerates the transfer of juice from the interior of the apple to its surface, creating a microenvironment at the apple-caramel interface where L. monocytogenes can rapidly grow to levels sufficient to cause disease when stored at room temperature.

Concepts: Listeria monocytogenes, Listeria, Listeriosis, Apple, Granny Smith, Apple Records, Eastwood, New South Wales

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The food-borne pathogen Listeria (L) monocytogenes is able to survive a variety of stress conditions leading to the colonization of different niches like the food processing environment. This study focuses on the hypervariable genetic hotspot lmo0443-lmo0449 haboring three inserts: the stress survival islet 1 (SSI-1), the single-gene insert LMOf2365_0481 and two homologous genes of the non-pathogenic species L. innocua: lin0464, a putative transcriptional regulator and lin0465, an intracellular PfpI protease. Our prevalence study revealed a different distribution of the inserts between human and food-associated isolates. The lin0464-lin0465 insert was predominantly found in food-associated strains of sequence type (ST) 121. Functional characterization of this insert showed that the putative PfpI protease Lin0465 is involved in alkaline and oxidative stress response, but not in acidic, gastric, heat, cold, osmotic and antibiotic stress. In parallel, deletion of lin0464 decreased the survival under alkaline and oxidative stress. The expression of both genes increased significantly under oxidative stress conditions independently of the alternative sigma factor σ(B) Furthermore, we showed that the expression of the protease lin0465 is regulated by the transcription factor lin0464 under stress conditions, suggesting that lin0464 and lin0465 form a functional unit.In conclusion, we identified a novel stress survival islet 2 (SSI-2), predominantly present in L. monocytogenes ST121 strains, beneficial for survival under alkaline and oxidative stress, potentially supporting adaptation and persistence of L. monocytogenes in food processing environments.IMPORTANCEListeria (L.) monocytogenes strains of ST121 are known to persist for months and even years in food processing environments, thereby increasing the risk of food contamination and listeriosis. However, the molecular mechanism underlying this remarkable niche-specific adaptation is still unknown. Here, we demonstrate that the genomic islet SSI-2, predominantly present in L. monocytogenes ST121 strains, is beneficial for survival under alkaline and oxidative stress conditions, which are routinely encountered in food processing environments. Our findings suggest that SSI-2 is part of a diverse set of molecular determinants contributing to niche-specific adaptation and persistence of L. monocytogenes ST121 strains in food processing environments.

Concepts: DNA, Genetics, Gene expression, Transcription, Oxidative stress, Listeria monocytogenes, Listeria, Listeriosis

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PURPOSE: To study the incidence and clinical characteristics of delayed cerebral thrombosis in bacterial meningitis patients. METHODS: We assessed the incidence and clinical characteristics of delayed cerebral thrombosis in adults with cerebrospinal fluid (CSF) culture-proven community-acquired bacterial meningitis included in a prospective nationwide study in The Netherlands performed from 2006 to 2012. RESULTS: Delayed cerebral thrombosis occurred in 11 of 1,032 episodes (1.1 %). CSF culture yielded Streptococcus pneumoniae in ten patients and Listeria monocytogenes in one. Adjunctive dexamethasone therapy was administered before or with the first dose of antibiotics in 9 of 11 patients; two patients were initially not treated with dexamethasone. All patients made good initial recovery, followed by sudden deterioration after 7-42 days. Cranial imaging studies showed multiple cerebral infarctions in all patients. The outcome was unfavorable in all but one patient. In an explorative analysis, patients with delayed cerebral thrombosis had eightfold higher complement C5a CSF concentrations on the diagnostic lumbar puncture as compared in those without delayed cerebral thrombosis (p = 0.04). CONCLUSION: Delayed cerebral thrombosis is a rare but devastating complication of bacterial meningitis. Adjunctive dexamethasone therapy seems to predispose patients with bacterial meningitis to this complication. We found some evidence that this thrombotic complication is associated with activation of the complement system.

Concepts: Bacteria, Streptococcus pneumoniae, Cerebrospinal fluid, Meningitis, Listeria monocytogenes, Listeriosis, Tuberculous meningitis, Lumbar puncture

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This study investigated the occurrence, concentration and key characteristics of Listeria monocytogenes in beef chain samples (n = 1100) over a 2-year period (July 2007-June 2009). Listeria monocytogenes was isolated from bovine hides (27%), pre-chill carcasses (14%) and ground beef (29%), but not from ready-to-eat (RTE) beef. The concentration of the pathogen in the majority (95%) of contaminated samples was low and detected by enrichment only. The highest concentrations recovered (100-200 CFU/g) were in ground beef samples. The most commonly isolated serotype group was 1/2a (58%) followed by 4b (12%), 1/2b (10%) and 1/2c (6%). A small portion (<5%) isolates had demonstrated resistance to key anti-microbials including ampicillin, vancomycin and gentamycin which are recommended treatment options for listeriosis. Pulsed-field gel electrophoresis showed indistinguishable profiles for a number of isolates recovered from the hide and carcass (after slaughter and dressing) of the same animals, highlighting the role of hides as a source of contamination. Equally, indistinguishable pulsotypes for isolates recovered at different stages and time points (up to 6 months apart) in the beef chain demonstrated the persistence of specific clones in the factory, process and distribution environments. Overall, the study demonstrated a high prevalence of clinically significant L. monocytogenes entering and progressing along the beef chain and highlights the needs to control cross-contamination during beef processing and distribution and the need for thorough cooking of raw beef products.

Concepts: Antibiotic resistance, Cattle, Penicillin, Meningitis, Listeria monocytogenes, Listeria, Listeriosis, Ampicillin

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The Listeria genus comprises 10 recognized species. L. monocytogenes causes listeriosis in humans and other animals primarily via contaminated food or animal feed. L. ivanovii causes listeriosis in animals and on rare occasions in humans. The identification of non-pathogenic species of Listeria in foods indicates that conditions exist that support the growth of pathogenic strains and is used to facilitate the implementation of control and prevention measures. This study shows the development and evaluation of a 5'exonuclease real-time PCR assay for the rapid identification of L. seeligeri, L. welshimeri, L. monocytogenes, L. ivanovii, L. grayi and L. innocua. The assay consists of two triplexes which were evaluated using fifty-three cultures of Gram-positive bacteria, including 49 Listeria spp. from human, animal, food or food processing environments. The assay was rapid, specific and reproducible and could identify each of the six species from a mixture of strains. The developed assay proved to be a powerful means of rapidly identifying Listeria species and could be usefully implemented in busy specialist reference laboratories. This article is protected by copyright. All rights reserved.

Concepts: Bacteria, Polymerase chain reaction, Microbiology, Identification, Listeria monocytogenes, Listeria, Listeriosis, Gram-positive bacteria

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Listeria monocytogenes 15G01, a strain belonging to the persistent pulsotype 5132, was isolated from a seafood processing plant in New Zealand. Simple monoculture assays using crystal violet staining showed good biofilm formation for this strain and it was therefore chosen to be further investigated in regard to its biofilm forming ability. To evaluate its behaviour in different conditions commonly encountered in food processing environments, biofilm assays and growth studies were performed using common laboratory media under a range of temperatures (20°C, 30°C and 37°C). Furthermore, the effects of incubation time and different environmental conditions including static, dynamic and anaerobic incubation on biofilm formation were investigated. Changes in the environmental conditions resulted in different biofilm phenotype of L. monocytogenes 15G01. We demonstrated that increasing temperature and incubation time led to a higher biofilm mass and that dynamic incubation has little effect on biofilm formation at 37°C but encourages biofilm formation at 30°C. Biofilm production at 20°C was minimal regardless of the medium used. We furthermore observed that anaerobic environment led to reduced biofilm mass at 30°C for all tested media but not at 37°C. Biofilm formation could not be narrowed down to one factor but was rather dependent on multiple factors with temperature and medium having the biggest effects.

Concepts: Microbiology, Environment, Natural environment, Listeria monocytogenes, Listeria, Listeriosis, Environmental science, Joseph Lister, 1st Baron Lister

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Listeria monocytogenes is a major foodborne pathogen that causes life-threatening illnesses in humans. With emergence of antibiotic resistance in L. monocytogenes, there is considerable interest in testing the efficacy of alternative therapies for controlling listeriosis in humans. This study investigated the efficacy of three phytochemicals, namely trans-cinnamaldehyde (TC), carvacrol (CR), and thymol (TY) in reducing L. monocytogenes virulence in the recently established invertebrate model, Galleria mellonella. In addition, the effect of phytochemicals on the transcription of antimicrobial peptide genes in G. mellonella (responsible for host defense) was investigated using real-time quantitative polymerase chain reaction. G. mellonella larvae were inoculated with L. monocytogenes (10(5) CFU/larvae) either with or without the subinhibitory concentration (chemical concentration not inhibiting bacterial growth) of phytochemicals. The larvae were incubated at 37 °C for 5 days, and their mortality was scored at 24-h intervals. The transcriptional response of the defense genes was studied in inoculated and uninoculated larvae at 6 h post challenge. The experiments were repeated at least six times with replicates. All phytochemicals enhanced the survival rates of G. mellonella infected with lethal doses of L. monocytogenes (P < 0.05). CR and TC at 0.01 % concentration were found to be the most effective treatments, and increased larval survival rates by 80 % and 50 %, respectively, on day 5 (P < 0.05). The phytochemicals also upregulated the expression of antimicrobial peptide genes in G. mellonella larvae challenged with L. monocytogenes (P < 0.05). Results suggest that TC, CR, and TY could potentially be used to control listeriosis. Further investigation in an appropriate mammalian model is warranted.

Concepts: DNA, Gene expression, Bacteria, Molecular biology, Microbiology, Listeria monocytogenes, Listeria, Listeriosis