Characterization ofListeriastrains isolated from soft and semi-soft cheeses

Lončarević, Semir; Bannerman, Elisabeth; Billé, Jacques; Danielsson-Tham, Marie-Louise; Tham, Wilhelm

doi:10.1006/fmic.1997.0177

Cited by 16 publications

(7 citation statements)

References 14 publications

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“…As a result of these properties, some food types are more prone to cause listeriosis than others. These foods include cold cuts and deli meats (Gottlieb et al 2006), fermented meat products (Uyttendaele et al 1999), smoked and fermented fish products (Huss et al 1995; Tham et al 2000), soft cheeses (Loncarevic et al 1998; Makino et al 2005; Pintado et al 2005, Bille et al 2006; Fretz et al 2010; Gaulin et al 2012) and, more recently, fruit (McCollum et al 2013).…”

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confidence: 99%

Use of used vs. fresh cheese brines and the effect of pH and salt concentration on the survival of Listeria monocytogenes

Schirmer

Heir

Lindstedt

et al. 2014

Journal of Dairy Research

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The aim of the study was to investigate how the use of fresh cheese brines compared with used brines and various combinations of pH and NaCl concentrations affected the survival of Listeria monocytogenes. Cheese brines from five Norwegian small scale cheese producers were analysed and showed great variations in pH (4·54-6·01) and NaCl concentrations (14·1-26·9 %). The survival of five strains of List. monocytogenes (two clinical isolates, two food isolates and one animal isolate) in four different cheese brines (three used and one fresh) was investigated. Results showed significant differences in survival both depending on the strains and the brines. Strains of human outbreak listeriosis cases showed greater ability to survive in the brines compared with food isolates and a List. monocytogenes reference strain (1-2 log10 difference after 200 d). All strains showed highest survival in the freshly prepared brine compared with the used brines. Molecular typing by multiple locus variable number tandem repeats analysis (MLVA) showed that there were no detectable alterations in the examined variable number tandem repeats of the genome in five strains after 200 d storage in any of the salt brines. Combined effects of pH (4·5, 5·25 and 6·0) and NaCl (15, 20 and 25 %) in fresh, filter sterilised brines on the survival of List. monocytogenes were examined and results showed that pathogen populations decreased over time in all brines. Death rates at any given NaCl concentration were highest at low pH (4·5) and death rates at any given pH were highest at low NaCl concentrations (15 %). In conclusion, the use of used brines reduced the survival of List. monocytogenes and a combination of low pH (4·5) and low salt concentrations (15 %) decreased the risk of List. monocytogenes survival compared with higher pH (5·25 or 6·0) and higher NaCl concentrations (20 or 25 %).

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confidence: 99%

Use of used vs. fresh cheese brines and the effect of pH and salt concentration on the survival of Listeria monocytogenes

Schirmer

Heir

Lindstedt

et al. 2014

Journal of Dairy Research

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“…Listeria monocytogenes is a ubiquitous gram-positive foodborne pathogen, with a widespread occurrence in, e.g., fresh meat and poultry (10), processed ready-to-eat meats (15), seafood (17), soft-style cheeses (18), and butter (19). This frequent occurrence is mainly explained by its ability to survive and grow at conditions associated with normal processing and distribution of food, such as refrigeration temperatures (27), high NaCl concentrations (20), or water activities (a w ) as low as 0.92 (24).…”

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confidence: 99%

Osmotic Stress Leads to Decreased Intracellular pH of Listeria monocytogenes as Determined by Fluorescence Ratio-Imaging Microscopy

Fang

Siegumfeldt

Budde

2004

Appl Environ Microbiol

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Intracellular pH (pH i ) of Listeria monocytogenes was determined after exposure to NaCl or sorbitol in liquid and solid media (agar). Both compounds decreased pH i , and recovery on solid medium was impaired compared to that in liquid medium. N,N-dicyclohexylcarbodiimide abolished pH i recovery, and lowering a w with glycerol showed no effect on pH i .Listeria monocytogenes is a ubiquitous gram-positive foodborne pathogen, with a widespread occurrence in, e.g., fresh meat and poultry (10), processed ready-to-eat meats (15), seafood (17), soft-style cheeses (18), and butter (19). This frequent occurrence is mainly explained by its ability to survive and grow at conditions associated with normal processing and distribution of food, such as refrigeration temperatures (27), high NaCl concentrations (20), or water activities (a w ) as low as 0.92 (24). Although L. monocytogenes is a neutrophile, it is tolerant to acidic conditions (5, 8), and Shabala et al. (22) demonstrated that L. monocytogenes maintained a constant intracellular pH (pH i ) at extracellular pH (pH ex ) values as low as 4.0. Information on the effect of osmotic stress on pH i of L. monocytogenes seems not to be available, and therefore the main objective of the present study was to investigate the relationship between pH i of L. monocytogenes and osmotic stress in liquid brain heart infusion broth (BHI) as well as on solid BHI (agar) by using fluorescence ratio-imaging microscopy according to the methods of Budde and Jakobsen (4).The strains of L. monocytogenes, EGD (kindly provided by Werner Goebel, Biozentrum, Universität Würzburg, Germany) and 4140 (the Danish Meat Research Institute, Roskilde, Denmark), were grown in BHI adjusted to pH 6.0 with HCl at 37°C for 10 h before use. Fluorescent labeling of the cells and image acquisition were performed essentially as previously described (4, 23), where washed cells were stained with 30 M 5,6-carboxyfluorescein diacetate-succinimidyl ester at 30°C for 30 min. Excitation with 490-and 435-nm wavelengths was performed through a 510-nm dichroic mirror, and emission was recorded through an 515-to 565-nm band pass filter on a Coolsnap fx camera (Photometrics, Tucson, Ariz.). Ratio imagings were performed by using MetaFluor, version 4.5 (Universal Imaging Corporation, West Chester, Pa.), and a minimum of 40 single cells was analyzed in each experiment. For pH calibration, labeled cells were permeabilized with ethanol (63% [vol/vol]) and were suspended in either BHI broth or were immobilized on the surface of BHI agar adjusted with HCl or NaOH to a pH in the range 5.5 to 8.5 (steps of 0.5), allowing pH i to equilibrate to pH ex . A polynomial model fitted to the data was subsequently used to calculate pH i .In liquid BHI the labeled cells were immobilized on the surface of an 8-well chamber slide (Lab-Tek II Chambered cover glass; Nalge Nunc International) by adding 100 l of bacterial suspension and allowing the cells to settle, followed by a brief rinse with phosphate-buffered saline before addition of liqui...

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“…Serotyping has revealed that strains are heterogeneously distributed; most major outbreaks of listeriosis (37) have been caused by strains belonging to serovar 4b, which has also been responsible for numerous sporadic cases (13,36). However, a low percentage of food samples is contaminated with strains of this serovar (1,25). Analysis of surface proteins, sequencing of virulence genes, and PCR-restriction enzyme analysis of virulence genes have revealed that differences are connected to the origin or typing characteristics of the strains (34,38,43,49,50,51).…”

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confidence: 99%

Expression of ActA, Ami, InlB, and Listeriolysin O in Listeria monocytogenes of Human and Food Origin

Jacquet

Gouin²,

Jeannel

et al. 2002

Appl Environ Microbiol

130

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Expression of proteins involved in the adhesion of Listeria monocytogenes to mammalian cells or in the intracellular life cycle of this bacterium, including listeriolysin O (LLO),). Of the strains isolated from patients with non-pregnancy-related cases of listeriosis, bacteremia was predominantly associated with group Ami1 strains (OR ‫؍‬ 1.89; P ‫؍‬ 1 ؋ 10 ؊2 ) and central nervous system infections were associated with group ActA2 strains (OR ‫؍‬ 3.04; P ‫؍‬ 1 ؋ 10 ؊3 ) and group ActA3 strains (OR ‫؍‬ 3.91; P ‫؍‬ 1 ؋ 10 ؊3 ).Since the transmission of human listeriosis was first shown to be food borne in 1981, Listeria monocytogenes has been recognized as a major food-borne pathogen. The severity of listeriosis, which can cause abortions, bacteremia, and central nervous system infections (CNSI) and has a high mortality rate (20 to 30% [13,36]), makes it a serious public health problem. In addition, the fact that various foods have been implicated in outbreaks of listeriosis (37) and the increase in product recalls (48) have led to serious economic problems associated with this bacterium.Based on present knowledge, any strain of L. monocytogenes should be considered potentially pathogenic for humans. Nevertheless, a number of observations suggests that L. monocytogenes virulence is heterogeneous. Serotyping has revealed that strains are heterogeneously distributed; most major outbreaks of listeriosis (37) have been caused by strains belonging to serovar 4b, which has also been responsible for numerous sporadic cases (13, 36). However, a low percentage of food samples is contaminated with strains of this serovar (1, 25). Analysis of surface proteins, sequencing of virulence genes, and PCR-restriction enzyme analysis of virulence genes have revealed that differences are connected to the origin or typing characteristics of the strains (34,38,43,49,50,51). The tests used to study L. monocytogenes pathogenicity include tissue culture assays and tests in which laboratory animals are used (5,7,9,44,46). These methods also have revealed heterogeneity in the virulence of strains. For example, counts of viable bacteria in spleens revealed that virulence levels varied from less than 10 3 to 10 8 CFU (5). However, there was no clear correlation between strain characteristics and the degree of virulence. Therefore, there are currently no laboratory tests which can predict the danger associated with L. monocytogenes strains.The mechanisms by which L. monocytogenes invades a host have been studied in detail (21). Listeriolysin O (LLO) is a 58-to 60-kDa secreted protein which allows the bacterium to escape from a phagocytosis vacuole (8, 15). LLO is a toxin which acts only on cholesterol-containing membranes in which cholesterol is considered the receptor. Nonhemolytic mutants are always avirulent in mice (15). However, the level of in vitro hemolysin production is not directly proportional to the virulence of a strain (18). InlB, which is a 67-kDa surface and secreted protein, is sufficient for entry of the bacterium into cells...

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Characterization ofListeriastrains isolated from soft and semi-soft cheeses

Cited by 16 publications

References 14 publications

Use of used vs. fresh cheese brines and the effect of pH and salt concentration on the survival of Listeria monocytogenes

Use of used vs. fresh cheese brines and the effect of pH and salt concentration on the survival of Listeria monocytogenes

Osmotic Stress Leads to Decreased Intracellular pH of Listeria monocytogenes as Determined by Fluorescence Ratio-Imaging Microscopy

Expression of ActA, Ami, InlB, and Listeriolysin O in Listeria monocytogenes of Human and Food Origin

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