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Monocytogenes Strains (monocytogene + strain)
Kinds of Monocytogenes Strains Selected AbstractsTranscriptome analysis of Listeria monocytogenes identifies three groups of genes differently regulated by PrfAMOLECULAR MICROBIOLOGY, Issue 6 2003Eliane Milohanic Summary PrfA is the major regulator of Listeria virulence gene expression. This protein is a member of the Crp/Fnr family of transcription regulators. To gain a deeper understanding of the PrfA regulon, we constructed a whole-genome array based on the complete genome sequence of Listeria monocytogenes strain EGDe and evaluated the expression profiles of the wild-type EGDe and a prfA -deleted mutant (EGDe ,prfA). Both strains were grown at 37°C in brain,heart infusion broth (BHI) and BHI supplemented with either activated charcoal, a compound known to enhance virulence gene expression, or cellobiose, a sugar reported to downregulate virulence gene expression in spite of full expression of PrfA. We identified three groups of genes that are regulated differently. Group I comprises, in addition to the 10 already known genes, two new genes, lmo2219 and lmo0788, both positively regulated and preceded by a putative PrfA box. Group II comprises eight negatively regulated genes: lmo0278 is preceded by a putative PrfA box, and the remaining seven genes (lmo0178,lmo0184) are organized in an operon. Group III comprises 53 genes, of which only two (lmo0596 and lmo2067) are preceded by a putative PrfA box. Charcoal addition induced upregulation of group I genes but abolished regulation by PrfA of most group III genes. In the presence of cellobiose, all the group I genes were downregulated, whereas group III genes remained fully activated. Group II genes were repressed in all conditions tested. A comparison of the expression profiles between a second L. monocytogenes strain (P14), its spontaneous mutant expressing a constitutively active PrfA variant (P14prfA*) and its corresponding prfA -deleted mutant (P14,prfA) and the EGDe strain revealed interesting strain-specific differences. Sequences strongly similar to a sigma B-dependent promoter were identified upstream of 22 group III genes. These results suggest that PrfA positively regulates a core set of 12 genes preceded by a PrfA box and probably expressed from a sigma A-dependent promoter. In contrast, a second set of PrfA-regulated genes lack a PrfA box and are expressed from a sigma B-dependent promoter. This study reveals that PrfA can act as an activator or a repressor and suggests that PrfA may directly or indirectly activate different sets of genes in association with different sigma factors. [source] Bacterial delivery of functional messenger RNA to mammalian cellsCELLULAR MICROBIOLOGY, Issue 5 2005Christoph Schoen Summary The limited access to the nuclear compartment may constitute one of the major barriers after bacteria-mediated expression plasmid DNA delivery to eukaryotic cells. Alternatively, a self-destructing Listeria monocytogenes strain was used to release translation-competent mRNA directly into the cytosol of epithelial cells, macrophages and human dendritic cells. Enhanced green fluorescent protein (EGFP)-encoding mRNA, adapted for translation in mammalian cells by linking an IRES element to the 5,-end of the egfp coding sequence, was produced by T7 RNA polymerase in the carrier bacteria upon entry into the cytosol where the mRNA is efficiently released from the lysed bacteria and immediately translated in eukaryotic host cells. Besides the much earlier expression of EGFP being detectable already 4 h after infection, the number of EGFP expressing mammalian cells obtained with this novel RNA delivery technique is comparable to or , especially in phagocytic cells , even higher than that obtained with the expression plasmid DNA delivery strategy. Accordingly, bacteria-mediated delivery of ovalbumin-encoding mRNA to macrophages resulted in efficient antigen processing and presentation in vitro indicating that this approach may also be adapted for the in vivo delivery of antigen-encoding mRNA leading to a more efficient immune response when applied to vaccine development. [source] Heteroduplex mobility assay for the identification of Listeria sp. and Listeria monocytogenes strains: application to characterisation of strains from sludge and food samplesFEMS IMMUNOLOGY & MEDICAL MICROBIOLOGY, Issue 3 2003N Garrec Abstract One hundred and ten Listeria sp. isolates from sewage sludge were identified according to phenotypic and genotypic methods. The Listeria sp. strains isolated from five types of sludge from three sewage treatment plants in Angers (France) and the surrounding area included L. monocytogenes (55.5%), L. innocua (29.1%), L. seeligeri (13.6%) and L. welshimeri (1.8%). The majority of L. monocytogenes strains belonged to serotypes 4b, 1/2b and 1/2a. Moreover, a heteroduplex mobility assay based on the 16S rRNA sequences was tested for its ability to identify the six species of the genus Listeria. This study, performed on 283 Listeria sp. strains from human, food and sewage sludge samples, showed that all the species were distinguishable from one another. L. innocua and L. seeligeri showed respectively three and two distinct banding patterns. Within L. monocytogenes, four groups (I,IV) were defined. The majority of food and environmental isolates were clustered in group I and it is noteworthy that group IV clustered epidemiologic isolates and strains belonging to serotypes 4b, 1/2a and 1/2b. [source] The growth limits of a large number of Listeria monocytogenes strains at combinations of stresses show serotype- and niche-specific traitsJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2008S. Van Der Veen Abstract Aims:, The aim of this study was to associate the growth limits of Listeria monocytogenes during exposure to combined stresses with specific serotypes or origins of isolation, and identify potential genetic markers. Methods and Results:, The growth of 138 strains was assessed at different temperatures using combinations of low pH, sodium lactate, and high salt concentrations in brain heart infusion broth. None of the strains was able to grow at pH , 4·4, aw , 0·92, or pH , 5·0 combined with aw , 0·94. In addition, none of the strains grew at pH , 5·2 and NaLac , 2%. At 30°C, the serotype 4b strains showed the highest tolerance to low pH and high NaCl concentrations at both pH neutral (pH 7·4) and mild acidic conditions (pH 5·5). At 7°C, the serotype 1/2b strains showed the highest tolerance to high NaCl concentrations at both pH 7·4 and 5·5. Serotype 1/2b meat isolates showed the highest tolerance to low pH in the presence of 2% sodium lactate at 7°C. ORF2110 and gadD1T1 were identified as potential biomarkers for phenotypic differences. Conclusions:, Differences in growth limits were identified between specific L. monocytogenes strains and serotypes, which could in some cases be associated with specific genetic markers. Significance and Impact of the Study:, Our data confirm the growth limits of L. monocytogenes as set out by the European Union for ready-to-eat foods and provides an additional criterion. The association of L. monocytogenes serotypes with certain stress responses might explain the abundance of certain serotypes in retail foods while others are common in clinical cases. [source] Influence of temperature on biofilm formation by Listeria monocytogenes on various food-contact surfaces: relationship with motility and cell surface hydrophobicityJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008G. Di Bonaventura Abstract Aims:, To assess the ability of Listeria monocytogenes to form biofilm on different food-contact surfaces with regard to different temperatures, cellular hydrophobicity and motility. Methods and Results:, Forty-four L. monocytogenes strains from food and food environment were tested for biofilm formation by crystal violet staining. Biofilm levels were significantly higher on glass at 4, 12 and 22°C, as compared with polystyrene and stainless steel. At 37°C, L. monocytogenes produced biofilm at significantly higher levels on glass and stainless steel, as compared with polystyrene. Hydrophobicity was significantly (P < 0·05) higher at 37°C than at 4, 12 and 22°C. Thirty (68·2%) of 44 strains tested showed swimming at 22°C and 4 (9·1%) of those were also motile at 12°C. No correlation was observed between swimming and biofilm production. Conclusions:,L. monocytogenes can adhere to and form biofilms on food-processing surfaces. Biofilm formation is significantly influenced by temperature, probably modifying cell surface hydrophobicity. Significance and Impacts of the Study:, Biofilm formation creates major problems in the food industry because it may represent an important source of food contamination. Our results are therefore important in finding ways to prevent contamination because they contribute to a better understanding on how L. monocytogenes can establish biofilms in food industry and therefore survive in the processing environment. [source] Response of Listeria monocytogenes to liquid smokeJOURNAL OF APPLIED MICROBIOLOGY, Issue 6 2008M. Guilbaud Abstract Aims:, To investigate the effect of liquid smoke on growth, survival, proteomic pattern and haemolytic potential of Listeria monocytogenes. Methods and Results:, Growth and survival curves were recorded in brain,heart infusion broth supplemented with three concentrations of liquid smoke. L. monocytogenes growth was inhibited in the presence of 15 ,g ml,1 phenol while a rapid decrease in cell viability occurred in the presence of 30 ,g ml,1 phenol. The proteome of L. monocytogenes cytosoluble proteins was slightly modified after 2-h incubation with 30 ,g ml,1 phenol but no protein already characterized in response to other known stresses was induced, except the protease ClpP. Liquid smoke inhibited the haemolytic potential without affecting hly gene expression, showing a potential inhibition of protein activity or stability. Conclusions:, The presence of liquid smoke in a rich medium strongly affected growth and survival of L. monocytogenes. Brief smoke stress affected the metabolic pathways and inhibited the haemolytic activity of L. monocytogenes. Significance and Impact of Study:, This study is a first step in the investigation of the influence of a smoked product on L. monocytogenes strains. [source] Viable but non-culturable Listeria monocytogenes on parsley leaves and absence of recovery to a culturable stateJOURNAL OF APPLIED MICROBIOLOGY, Issue 4 2007N. Dreux Abstract Aims:, To investigate the presence of viable but non-culturable Listeria monocytogenes during survival on parsley leaves under low relative humidity (RH) and to evaluate the ability of L. monocytogenes to recover from VBNC to culturable state under satured humidity. Methods and Results:, Under low RH (47,69%) on parsley leaves, the initial number of L. monocytogenes populations counted on non selective media (109 L. monocytogenes per leaf on TSA) was reduced by 6 log10 scales in 15 days, whereas number of viable L. monocytogenes counted under the microscope was reduced by 3,4 log10 scales, indicating the presence of VBNC cells. This was demonstrated on three L. monocytogenes strains (EGDe, Bug 1995 and LmP60). Changing from low to 100% RH permitted an increase of the culturable counts of L. monocytogenes and this growth was observed only when residual culturable cells were present. Moreover, VBNC L. monocytogenes inoculated on parsley leaves did not become culturable after incubation under 100% RH. Conclusions:, Dry conditions induced VBNC L. monocytogenes on parsley leaves but these VBNC were likely unable to recover culturability after transfer to satured humidity. Significance and Impact of Study:, Enumeration on culture media presumably under-estimates the number of viable L. monocytogenes on fresh produce after exposure to low RH. [source] The diversity of Listeria monocytogenes strains from 10 Icelandic sheep farmsJOURNAL OF APPLIED MICROBIOLOGY, Issue 5 2004K.B. Gudmundsdottir Abstract Aims:, The purpose of this study was to examine the diversity of Listeria monocytogenes strains from healthy sheep, winter feed and environment of sheep farms in Iceland. Methods and Results:, A total of 104 L. monocytogenes isolates from animals, winter feed and environment on 10 Icelandic sheep farms were compared by serotyping, ribotyping, and pulsed-field gel electrophoresis with ApaI and AscI. The isolates were divided into 24 genotypes, all identified as serovars 1/2a, 1/2b, or 4b. Nine genotypes were detected on more than one farm. On three of the farms there seemed to be a dominant strain of L. monocytogenes. Isolates from incidents of listeriosis in animals occurring on two of the farms belonged to the genotype most commonly found on the particular farm. Nine of the 24 genotypes found on the sheep farms have been associated with disease in animals and/or humans elsewhere in Iceland. Conclusions:, Certain strains of L. monocytogenes seem to be widely distributed on Icelandic sheep farms. On some farms there appears to be a dominant strain of L. monocytogenes. Incidents of listeriosis in animals may tend to be associated with strains commonly found on the farm. Significance and Impact of the Study:, This study demonstrates the diversity of L. monocytogenes present in healthy sheep and their environment. [source] INDICATOR AND PATHOGENIC BACTERIA IN GUACAMOLE AND THEIR BEHAVIOR IN AVOCADO PULPJOURNAL OF FOOD SAFETY, Issue 4 2001SOFÍ M. ARVIZU-MEDRANO ABSTRACT The presence of some indicator microorganisms and pathogenic bacteria in guacamole sampled from restaurants and street vendors, and the behavior of Salmonella spp., Staphylococcus aureus, and Escherichia coli O157:H7 were studied in avocado pulp. Coliform, yeast and mold populations showed a wide dispersion, in agreement with the diversity of sanitary conditions observed among places sampled. The frequency of Salmonella spp., Listeria monocytogenes, and E. coli were 1.3, 16.0, and 60.0 %, respectively; with higher numbers among street vendors. Populations of E. coli ranged from 29 to 3800 NMP/g and S. aureus from 2.95 to 5.35 log CFU/g. Thirteen out of 16 hemolytic L. monocytogenes strains were pathogenic for mice. In avocado pulp Salmonella spp. and E. coli O157:H7 showed a lag phase close to 3 h, and a generation time of 54 min and 1.23 h, respectively. No growth of pathogens was observed in avocado pulp stored at 4-7C. [source] Identification of Listeria innocua Surrogates for Listeria monocytogenes in Hamburger PattiesJOURNAL OF FOOD SCIENCE, Issue 4 2008E.C. Friedly ABSTRACT:,Listeria innocua M1 has been used by many researchers as a nonpathogenic thermal processing surrogate for Listeria monocytogenes. However, L. innocua M1 has been criticized because its thermal survivability characteristics are not as closely parallel to L. monocytogenes as some would like in a variety of foods and processing conditions. The present study was conducted to compare multiple L. innocua and L. monocytogenes strains to validate L. innocua M1 as the ideal surrogate under high-temperature thermal processing conditions for L. monocytogenes. The D - and z -values of L. innocua M1, L. innocua strain SLCC 5639 serotype (6a), SLCC 5640 (6b), SLCC 2745 (4ab), and L. monocytogenes F4243 (4b) were calculated for raw hamburger patties. Hamburger patties were inoculated with 107,8 CFU/g of L. monocytogenes or L. innocua. Samples were heat treated at 4 temperatures (62.5 to 70 °C). At each temperature, the decimal reduction time (D -value) was obtained by linear regression of survival curves. The D - and z -values were determined for each bacterium. The D -values of L. innocua and L. monocytogenes serotypes ranged from 3.17 to 0.13 min at 62.5 to 70 °C, and the z -values of L. innocua and L. monocytogenes were 7.44 to 7.73 °C. Two of the 4 L. innocua serotypes used in this experiment have the potential for use as surrogates in hamburger meat with varying margins of safety. L. innocua M1 should serve as the primary nonpathogenic surrogate with the greatest margin of safety in verifying a new thermal process to destroy L. monocytogenes. [source] Mathematical Frameworks for Modeling Listeria Cross-contamination in Food-JOURNAL OF FOOD SCIENCE, Issue 6 2004D.W. Schaffner ABSTRACT: The possibility of modeling the cross-contamination of Listeria species, total Listeria monocytogenes, or specific L. monocytogenes strains using a quantitative mathematical model using Monte Carlo simulation techniques is proposed. This article illustrates this approach using 2 different models: one that tracks L. monocytogenes number and prevalence for 4 different strains (Model I) and one that tracks only prevalence for a single strain (Model II). These models have been developed to provide a starting framework for predictive modelers and scientists studying L. monocytogenes to begin research together with the ultimate goal of understanding and controlling L. monocytogenes in food-processing plants. [source] Efficacy of sodium hypochlorite and peracetic acid in sanitizing green coconutsLETTERS IN APPLIED MICROBIOLOGY, Issue 3 2009E.H.M. Walter Abstract Aims:, To evaluate the efficacy of sanitizing green coconuts (Cocos nucifera L.) through the treatment applied by juice industries using sodium hypochlorite and peracetic acid. Methods and Results:, The surface of the fruits was inoculated with a mixture of five Listeria monocytogenes strains. The treatments consisted in immersing the fruits for 2 min at room temperature in sodium hypochlorite solution containing 200 mg l,1 residual chlorine at pH 6·5, and 80 mg l,1 solution of peracetic acid or sterile water. Bacterial populations were quantified by culturing on trypticase soy agar supplemented with yeast extract and Oxford selective culture medium; however, recovery was higher on the nonselective medium. Immersion in water produced a reduction in the L. monocytogenes population of 1·7 log10 CFU per fruit, while immersion in sodium hypochlorite and peracetic acid solutions resulted in population reductions of 2·7 and 4·7 log10 CFU per fruit respectively. Conclusions:, The treatments studied are efficient to green coconuts. Significance and Impact of the Study:, Sanitation of green coconut is one of the most important control measures to prevent the contamination of coconut water. This article provides information that shows the adequacy of sanitizing treatments applied by the juice industries. [source] In vitro synergistic effect of gentamicin with the anti-inflammatory agent diclofenac against Listeria monocytogenesLETTERS IN APPLIED MICROBIOLOGY, Issue 6 2009N.K. Dutta Abstract Aims:, A total of nine Listeria monocytogenes strains (seven serotypes) were studied to ascertain whether the non-steroidal anti-inflammatory drug diclofenac (Dc) used in combination with the conventional antilisterial antibiotic gentamicin (Gm) or ampicillin (Am) synergistically augments the efficacy of the antibiotic in vitro. Methods and Results:, The effect of combination was evaluated by the checkerboard method to obtain a fractional inhibitory concentration (FIC) index followed by kill curves. Dc was synergistic with Gm (FIC 0·37) and there was indifference with Am (FIC 1) against L. monocytogenes ATCC 51774. The magnitude of the differences between killing by a single agent and the combination observed at 24 h was significant (P < 0·05) for Dc plus Gm but not Dc plus Am. Conclusions:, Thus, the ability of extended antibiotic therapy may be improved with the help of this synergistic drug pair in listeriosis. Significance and Impact of the Study:, Such findings may indicate parallel administration of anti-inflammatory and anti listeriosis drugs. [source] A small outbreak of listeriosis potentially linked to the consumption of imitation crab meatLETTERS IN APPLIED MICROBIOLOGY, Issue 2 2000J.M. Farber A small outbreak of listeriosis involving two previously healthy adults occurred in Ontario. Food samples obtained from the refrigerator of the patients included imitation crab meat, canned black olives, macaroni and vegetable salad, spaghetti sauce with meatballs, mayonnaise and water. All of the samples except the water contained Listeria monocytogenes. The three most heavily contaminated samples were the imitation crab meat, the olives and the salad which contained 2·1 × 109, 1·1 × 107 and 1·3 × 106 cfu g,1, respectively. L. monocytogenes serotype 1/2b was isolated from the patients, as well as from the opened and unopened imitation crab meat. Molecular typing of the isolates by both randomly amplified polymorphic DNA (RAPD) and pulsed-field gel electrophoresis (PFGE) typing demonstrated the imitation crab meat and clinical strains to be indistinguishable. Challenge studies performed with a pool of L. monocytogenes strains showed that imitation crab meat, but not olives, supported growth of the organism. In this study we have shown for the first time the potential involvement of imitation crab meat in a small outbreak of listeriosis. In terms of disease prevention, temperature control is critical to prevent or reduce the growth of this foodborne pathogen. In addition, with refrigerated products having a long (> 30 d) shelf life, additional safety factors must be used to prevent the growth of foodborne pathogens such as L. monocytogenes. [source] | |||||||||||||