[ON SOME METABOLIC AND CULTURAL ASPECTS OF LISTERIA MONOCYTOGENES. I. PHOSPHATASE ACTIVITY OF LISTERIA MONOCYTOGENES].
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Biochemical Phenomena↗
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Method extension study to validate applicability of AOAC Official Method 997.03 visual immunoprecipitate assay (VIP) for Listeria monocytogenes and related Listeria spp. from environmental surfaces: collaborative study.
Test portions from 3 environmental surface types, representative of typical surfaces found in a food production facility, were analyzed by the Visual Immunoprecipitate assay (VIP) and the U.S. Department of Agriculture/Food Safety and Inspection Service (USDA/FSIS) culture method for Listeria monocytogenes and related Listeria species. In all cases, naturally contaminated environmental test samples were collected from an actual food production facility by sponge or swab. Test samples from concrete surfaces were collected by both swab and sponge; sponge test samples were collected from rubber surfaces, and swabs were used to sample steel surfaces. Test portions from each surface type were simultaneously analyzed by both methods. A total of 27 laboratories, representing government agencies as well as private industry in both the United States and Canada, participated in the study. During this study, a total of 615 test portions and controls was analyzed and confirmed, of which 227 were positive and 378 were negative by both methods. Nine test portions were positive by culture, but negative by the VIP. Five test portions were negative by culture, but positive by the VIP. Four test portions were negative by VIP and by culture, but confirmed positive when VIP enrichment broths were subcultured to selective agars. The data reported here indicate that the VIP method and the USDA/FSIS culture method are statistically equivalent for detection of L. monocytogenes and related Listeria species from environmental surfaces taken by sponges or swabs.
Bacteriological Techniques↗
[ON SOME METABOLIC-CULTURAL CHARACTERISTICS OF LISTERIA MONOCYTOGENES. 3. LIPASE ACTIVITY OF LISTERIA MONOCYTOGENES].
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Bacteriological Techniques↗
[ON SOME METABOLIC AND CULTURAL CHARACTERISTICS OF LISTERIA MONOCYTOGENES. II. ARYLSULFATASE ACTIVITY OF LISTERIA MONOCYTOGENES].
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Arylsulfatases↗
Contamination pattern of Listeria monocytogenes and other Listeria spp. in a salmon slaughterhouse and smoked salmon processing plant.
A smoked salmon processing plant including a smokehouse and a slaughterhouse was examined for the occurrence of Listeria monocytogenes and other Listeria spp. From a total of 475 samples the overall frequency of L. monocytogenes was 16%, while other Listeria spp. were found in 22% of the samples. L. monocytogenes was most often detected in samples from the smokehouse, where 29% of the environmental and 26% of the fish samples during processing contained the bacteria. 17% of the fish raw material to the smokehouse were contaminated, while 11% of the samples from vacuum-packed smoked salmon were positive for L. monocytogenes. The slaughterhouse was sporadically contaminated, but L. monocytogenes was not found in 50 samples of slaughtered fish. L. monocytogenes was found in the seawater outside the slaughterhouse. Multilocus enzyme electrophoresis divided the isolated L. monocytogenes strains into 11 electrophoretic types (ETs). One ET, ET-6, which is the most common ET in Norway, seemed to have colonized the smokehouse. Isolates from the seawater, from the slaughterhouse and from fish coming into the smokehouse, before filleting, were other ETs.
Abattoirs↗
Optical forward-scattering for detection of Listeria monocytogenes and other Listeria species.
We demonstrate here the development of a non-invasive optical forward-scattering system, called 'scatterometer' for rapid identification of bacterial colonies. The system is based on the concept that variations in refractive indices and size, relative to the arrangement of cells in bacterial colonies growing on a semi-solid agar surface will generate different forward-scattering patterns. A 1.2-1.5mm colony size for a 1mm laser beam and brain heart infusion agar as substrate were used as fixed variables. The current study is focused on exploring identification of Listeria monocytogenes and other Listeria species exploiting the known differences in their phenotypic characters. Using diffraction theory, we could model the scattering patterns and explain the appearance of radial spokes and the rings seen in the scattering images of L. monocytogenes. Further, we have also demonstrated development of a suitable software for the extraction of the features (scalar values) calculated from images of the scattering patterns using Zernike moment invariants and principal component analysis and were grouped using K-means clustering. We achieved 91-100% accuracy in detecting different species. It was also observed that substrate variations affect the scattering patterns of Listeria. Finally, a database was constructed based on the scattering patterns from 108 different strains belonging to six species of Listeria. The overall system proved to be simple, non-invasive and virtually reagent-less and has the potential for automated user-friendly application for detection and differentiation of L. monocytogenes and other Listeria species colonies grown on agar plates within 5-10 min analysis time.
Biosensing Techniques↗
Specificity of the anamnestic response produced by Listeria monocytogenes or Mycobacterium tuberculosis to challenge with Listeria monocytogenes.
When mice immunized with Listeria monocytogenes were given a second injection of listeria, they showed an anamnestic immune response to intravenous challenge with listeria, as measured by enumeration of the viable infecting organisms in the spleens of the infected animals. This response was independent of the effects of the challenge dose. When mice immunized with living or heat-killed attenuated mycobacterial cells were boosted with living H37Ra, there was also an accelerated response to listeria challenge. The response was greater in the mice given the primary immunization with living cells than in those immunized with heat-killed cells. The response to listeria challenge in mice immunized and boosted with mycobacteria was of less magnitude than that in the mice immunized and boosted with listeria. Growth of listeria in the mice immunized and boosted with mycobacteria was retarded only during the first 2 days of the infection, whereas the infecting listeria in mice immunized and boosted with listeria were permanently inactivated. Mice immunized with mycobacterial ribosomal fraction and restimulated with living mycobacterial cells showed no accelerated response to listeria challenge. It is evident from these results that resistance to these organisms is specifically evoked, but that once evoked it is not completely nonspecific in action. Also, the resistance produced by the mycobacterial ribosomal fraction to challenge with mycobacteria is completely specific in action. Therefore, it has been shown that there are two mechanisms involved in acquired immunity to facultative, intracellular parasites. One is nonspecific and mediated by activated macrophages. The other is specific and mediated by a mechanism as yet unknown.
Animals↗
Discrimination of Listeria monocytogenes from other Listeria species by ligase chain reaction.
A ligase chain reaction assay based on a single-base-pair difference in the V9 region of the 16S rRNA gene (16S rDNA) was developed to distinguish between Listeria monocytogenes and other Listeria species. For this purpose, two pairs of primers were designed, with one primer of each pair being radioactively labeled. The ligated product was separated from the primers by denaturing polyacrylamide gel electrophoresis and then detected by autoradiography. To achieve a higher sensitivity, the 16S rDNA was initially amplified by polymerase chain reaction prior to the ligase chain reaction. The ligase chain reaction was tested on 19 different Listeria species and strains and proved to be a highly specific diagnostic method for the detection of L. monocytogenes.
Base Sequence↗
Comparison of a cold enrichment and the FDA method for isolating Listeria monocytogenes and other Listeria spp. from ready-to-eat food on retail sale in the U.K.
A cold enrichment and the modified FDA selective enrichment method were compared for their ability to detect Listeria monocytogenes and other Listeria species from various ready-to-eat foods on sale in the UK. Of 57 food samples examined using cold enrichment, five yielded L. monocytogenes, and two L. innocua. The FDA enrichment method yielded three samples positive for L. monocytogenes only. Foods examined included soft cheeses, fermented meat sausages, pates and salads.
Animals↗
Ultrastructural studies on antimicrobial efficacy of thyme essential oils on Listeria monocytogenes.
OBJECTIVES: Listeria monocytogenes has gained increasing attention as a pathogen of public health importance owing to large numbers of food-borne outbreaks of listeriosis. Because of negative consumer perception of chemical preservatives, attention is shifting towards natural alternatives. Particular interest has been focused on the potential application of plant essential oils. The objective of the present study was to determine ultrastructural changes brought about by essential oils from two types of thyme, Thymus eriocalyx and Thymus x-porlock, on Listeria monocytogenes. MATERIALS AND METHODS: Minimal inhibitory (MIC) and minimal bactericidal (MBC) concentrations and bactericidal kinetics of the oils were determined. Listeria monocytogenes were treated with essential oils from two thyme species and observed under a transmission electron microscope. RESULTS: The oils from the above plants were found to be strongly antimicrobial. Analysis of the oils by gas chromatography and gas chromatography/mass spectrometry lead to the identification of 18 and 19 components in T. eriocalyx and T. x-porlock oils, respectively. Listeria monocytogenes treated with essential oils from the two thyme species exhibited a thickened or disrupted cell wall with increased roughness and lack of cytoplasm. CONCLUSION: The antilisterial effects of thyme oil are stronger than the action of electric shocks in combination with nisin reported in the literature. It is concluded that essential oils such as thyme oil, which inhibited the growth of L. monocytogenes at low concentrations, could be considered as preservative materials for some kinds of foods; they could find an application as additives to foodstuffs in storage to protect them from listerial contamination.
Anti-Bacterial Agents↗
Application of a multiplex polymerase chain reaction assay for the simultaneous confirmation of Listeria monocytogenes and other Listeria species in turkey sample surveillance.
A multiplex polymerase chain reaction was developed to simultaneously identify Listeria monocytogenes and species of the genus Listeria. Two sets of primers were used, with the first amplifying a 938-bp region of the 16S rRNA gene that is highly conserved in all Listeria species and the second amplifying a 174-bp region of the listeriolysin (hlyA) gene of L. monocytogenes. Thus, isolates of Listeria spp. yield a single 938-bp product, whereas L. monocytogenes isolates yield both the 938-bp product and a 174-bp product. The specificity of the assay was verified with all six Listeria species and 11 serotypes of L. monocytogenes, as well as nonrelated bacteria. The multiplex PCR assay was used to determine the incidence of Listeria spp., especially L. monocytogenes, in mechanically separated turkey samples (n = 150 samples). L. monocytogenes strains were selected by using the University of Vermont two-step enrichment protocol and plating to selective Palcam agar. The multiplex PCR assay was used for verification of presumptive Listeria colonies. Approximately 38% of mechanically separated turkey samples (57 of 150) yielded L. monocytogenes; an additional 18% of these samples (27 of 150) harbored other Listeria spp. Fifty-one percent (29 of 57) of the L. monocytogenes isolates were of serogroup 1, 44% (25 of 57) were of serogroup 4, and 2% (1 of 57) were assigned to serogroups other than 1 and 4.
Animals↗
International Life Sciences Institute North America Listeria monocytogenes strain collection: development of standard Listeria monocytogenes strain sets for research and validation studies.
Research and development efforts on bacterial foodborne pathogens, including the development of novel detection and subtyping methods, as well as validation studies for intervention strategies can greatly be enhanced through the availability and use of standardized strain collections. These types of strain collections are available for some foodborne pathogens, such as Salmonella and Escherichia coli. We have developed a standard Listeria monocytogenes strain collection that has not been previously available. The strain collection includes (i) a diversity set of 25 isolates chosen to represent a genetically diverse set of L. monocytogenes isolates as well as a single hemolytic Listeria innocua strain and (ii) an outbreak set, which includes 21 human and food isolates from nine major human listeriosis outbreaks that occurred between 1981 and 2002. The diversity set represents all three genetic L. monocytogenes lineages (I, n = 9; II, n = 9; and III, n = 6) as well as nine different serotypes. Molecular subtyping by EcoRI automated ribotyping and pulsed-field gel electrophoresis (PFGE) with AscI and ApaI separated the 25 isolates in the diversity set into 23 ribotypes and 25 PFGE types, confirming that this isolate set represents considerable genetic diversity. Molecular subtyping of isolates in the outbreak set confirmed that human and food isolates were identical by ribotype and PFGE, except for human and food isolates for two outbreaks, which displayed related but distinct PFGE patterns. Subtype and source data for all isolates in this strain collection are available on the Internet and are linked to the PathogenTracker database (www.pathogentracker.com), which allows the addition of new, relevant information on these isolates, including links to publications that have used isolates from this collection. We have thus developed a core L. monocytogenes strain collection, which will provide a resource for L. monocytogenes research and development efforts with centralized Internet-based data curation and integration.
Animals↗
The VIT technology for rapid detection of Listeria monocytogenes and other Listeria spp.
Detection of Listeria monocytogenes is generally performed in a two-step cultural enrichment process and takes on average 1 week until the biochemical identification of a L. monocytogenes suspicious colony is completed. However, food processing companies depend increasingly on test methods, which attempt to generate results comparable to standard methods but in reduced time-frame and which allow to release produced batches dependent on such results. In the present study, the vermicon identification technology (VIT), a rapid commercial test system using fluorescently labelled gene probes, was compared to a cultural standard method. In total, 298 naturally contaminated samples were analysed. The sensitivity and the specificity of the VIT system were 100% for the detection of L. monocytogenes and 97.1% and 100%, respectively, for the detection of the genus Listeria.
Animals↗
Plasmids in Listeria monocytogenes and other Listeria species.
One hundred and twenty-two food, clinical, and veterinary strains of Listeria monocytogenes were examined for the presence of plasmids. Twenty-five (20%) contained plasmids, which varied from 1.3 to 66 MDa in size. Of 10 strains of other Listeria species (L. innocua, L. ivanovii, L. welshimeri, L. seeligeri, L. grayi, and L. murrayi) examined, seven (70%) contained plasmids, varying from 38 to 53 MDa. No strains with multiple plasmids were found. Plasmids of identical size were isolated from related strains in some, although not all, cases. The presence of a plasmid in a strain was not related to phenotypic characters of known extrachromosomal inheritance.
Animals↗
Prevalence of Listeria monocytogenes and other Listeria spp.in smoked and 'gravad' fish.
Altogether 150 samples of vacuum-packed fish were examined for the presence of Listeria species. Listeria monocytogenes were isolated from 12 of 58 'gravad' fish samples, 3 of 26 cold-smoked and one of 66 hot-smoked fish samples. Ten of these 16 positive samples harboured more than 100 L. monocytogenes cfu/g. The highest level (132,000) was found in a sample of hot-smoked rainbow trout (Oncorhynchus mykiss). Serogroup 1/2 was most frequently found, followed by 4 and 3. One sample of gravad rainbow trout harboured more than one serogroup of L. monocytogenes. L. innocua and L. seeligeri were isolated from 12 and 1 samples, respectively.
Animals↗
Evaluation of VIDAS listeria monocytogenes II (LMO2) immunoassay method for the detection of Listeria monocytogenes in foods: collaborative study.
A multilaboratory study was conducted to compare the VIDAS Listeria monocytogenes II (LMO2) immunoassay and the standard cultural methods for the detection of Listeria monocytogenes in foods. Five food types-vanilla ice cream, brie cheese, cooked roast beef, frozen green beans, and frozen tilapia fish-at 3 levels were analyzed by each method. A total of 26 laboratories representing government and industry participated. In this study, 1404 test portions were analyzed of which 1152 were used in the statistical analysis. There were 448 positive by the VIDAS LMO2 assay and 457 positive by the standard culture methods. A chi2 analysis of each of the 5 food types, at the 3 inoculation levels tested, was performed. The resulting chi2 value, 0.36, indicates that overall, there are no statistical differences between the VIDAS LMO2 assay and the standard methods at the 5% level of significance.
Food Microbiology↗
The gene coding for protein p60 of Listeria monocytogenes and its use as a specific probe for Listeria monocytogenes.
The gene of Listeria monocytogenes that encodes a major extracellular protein (p60) was cloned in Escherichia coli. The gene was designated iap, as p60 was previously shown to represent an invasion-associated protein (M. Kuhn and W. Goebel, Infect. Immun. 57:55-61, 1989). The recombinant E. coli clone expressed p60, as shown by immunoblotting. The complete nucleotide sequence of iap was determined. The deduced amino acid sequence of p60 (484 amino acids) contains a putative N-terminal signal sequence of 27 amino acids and an extended repeat region consisting of 19 threonine-asparagine units. Hybridization with the entire iap gene revealed the presence of homologous sequences in most other Listeria species. In contrast, a 400-base-pair internal iap probe which contained the whole repeat region hybridized only with genomic DNA from L. monocytogenes. Four oligonucleotides previously described as specific probes for the detection of L. monocytogenes (A. R. Datta, B. A. Wentz, D. Shook, and M. W. Trucksess, Appl. Environ. Microbiol. 54:2933-2937, 1988) were shown to be part of the iap gene.
Amino Acid Sequence↗
Influence of environmental parameters on phosphatidylcholine phospholipase C production in Listeria monocytogenes: a convenient method to differentiate L. monocytogenes from other Listeria species.
The ability to produce phosphatidylcholine phospholipase C (lecithinase) is associated with virulence in pathogenic species of Listeria. Levels of production vary greatly among members of the genus, and this virulence factor is not readily detectable in many members of the pathogenic species on conventional agar media containing egg yolk, a common substrate for the enzyme. In this study, the influence of a variety of environmental parameters, including temperature, pH, and salt concentration, on the production of lecithinase by a number of strains was evaluated. Lecithinase production by Listeria monocytogenes LO28 in brain heart infusion medium was optimal at 1.75 to 2.0% NaCl; pH 7.0 to 7.3, and 37 to 40 degrees C, and the presence of oxygen had no effect. In a chemically defined medium, the optimal NaCl concentration and temperature were lower at 0.75 to 1.0% NaCl and 33.5 degrees C. As detection of virulence factors is useful to assist in the identification and differentiation of Listeria species, this report shows that lecithinase activity can conveniently be detected within 36 h on a relatively inexpensive medium. Under the conditions described, L. monocytogenes could be distinguished from other members of the genus as a result of distinct lecithin degradation which was not evident in L. innocua, L. seeligeri, L. ivanovii, L. welshimeri, or L. murrayi/grayi.
Culture Media, Serum-Free↗