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  • 1
    Publication Date: 1976-05-01
    Print ISSN: 0022-5193
    Electronic ISSN: 1095-8541
    Topics: Biology
    Published by Elsevier
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food safety 14 (1994), S. 0 
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recovery of injured cells of a 90% heat kill of Listeria monocytogenes strain Lm82 in Trypticase soy yeast extract broth (TSBYE) at 30C was determined in enrichment broth and modified enrichment broth. Although the surviving population was heterogeneous with respect to degree of damage, two fractions of surviving cells defined as moderately and severely damaged were considered. Progeny of moderately damaged survivors (NaCl-sensitive but not enrichment medium-sensitive) increased about 100-fold in 5 h; severely damaged cells (enrichment medium- and NaCl-sensitive) did not grow in this time period. Most of the severely damaged cells required 20 h or longer to recover in TSBYE and even longer in TSBYE plus selective agents. Recovery was accelerated either by adding sodium pyruvate or by reducing the oxygen level. The results were used to design a Mark I preenrichment/enrichment protocol based on the U.S. Food and Drug Administration's selective enrichment broth.
    Type of Medium: Electronic Resource
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  • 3
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food safety 13 (1993), S. 0 
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: A study was made of the competitiveness toward Listeria monocytogenes (Lm82) in Listeria enrichment broth (LEB) by bacteria isolated from foods and by strains of Enterococcus and other Gram-positive bacteria. Competitive (i.e., able to mask during enrichment in LEB for 24 h) and noncompetitive bacteria were tested for production ofanti-Lm82 agents in diffusion zone assays on deMann-Rogosa-Sharpe (MRS) agar with added beta-glycero-phosphate (MRSB) and in Listeria enrichment agar (LEA). Enterococci were the most active competitors. The presence of small (2–6 mm diameter) inhibitory zones on MRSB correlated significantly with competitive activity in LEB; however, the correlation was not due to the metabolic activity that produced inhibitory zones on MRSB. Zone-producing bacteria were more likely to be competitors than were nonzone producers, but not all zone producers were competitors. Similarly, about 15% of bacteria that did not produce zones were competitive. The few inhibitory zones on LEA indicated that competitor activity in the selective enrichment broth may only rarely be due to the production of diffusible inhibitors. The most important factor in competitiveness was the ability of enterococci and some other bacteria to maintain superior numbers in the presence of prolisterial selective agents in LEB. With their superior numbers, competitors significantly decreased the pH of LEB. faster than did noncompetitors. Diffusible inhibitors produced in LEA by bacteria may also contribute significantly to competitiveness.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: The effect of aerobic mesophilic microfloral concentration on the isolation of Listeria monocytogenes LM82 was studied in 31 (18 cheeses and 7 noncheese) retail foods having standard plate counts of 101 to 108 colony forming units (CFU)/g. Foods were spiked with L. monocytogenes and enriched at 30°C for 24 h in a selective enrichment broth used in a U.S. Food and Drug Administration method. Inoculum levels for isolation on modified McBride agar ranged from 0.1 to 〉 5 × 103 with a geometric mean value of 5 inoculated CFU/g or 1.4 CFU/g. Pure Enterococcus (Streptococcus) faecalis (0 to 6 × 106 inoculated CFU/mL) in the absence of food matrix had no effect on the enrichment of L. monocytogenes. Ease of isolation of LM82 was independent of the food microflora concentration both generally and in the specific food type of 9 Brie cheeses. Competition, when it occurs, therefore, may be due to specific bacterial competitors rather than bacterial numbers.
    Type of Medium: Electronic Resource
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  • 5
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food safety 13 (1993), S. 0 
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Recovery of heat-injured Listeria monocytogenes strain LM82 was evaluated quantitatively in Listeria enrichment broth (LEB) and in enriched cultures of cooked shrimp and Brie cheese. LM82 cells [108 colony forming units (CFU)/ml] were heated for 60 min at 52C in phosphate-buffered saline. After 24 and 48 h enrichment, injured LM82 (6 replicates at each of 5 inoculation levels) were isolated on 3 selective media: lithium chloride-phenylethanol-moxalactam agar (LPMA), modified McBride agar (MMA) and Oxford agar (OXA). The recovery limit was expressed as a 50% end point value (RL50), which is the calculated inoculation value necessary to recover LM82 on half of the replicates of each type of isolation agar plate after streaking from the enrichment of measured inoculum. The RL50 values for injured cells were comparable to those of uninjured cells after 48 h enrichment in LEB without food. The type of isolation agar did not affect the RL50 value, although with food, MMA gave consistently but not significantly higher values, i.e., recovery inferior to that of LPMA and OXA. RL50 values were higher in Brie and cooked shrimp, presumably because of the competitive microflora in those foods. Addition of lactose or pyruvate to LEB improved recovery but had little or no effect when foods were present.
    Type of Medium: Electronic Resource
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  • 6
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food safety 11 (1991), S. 0 
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Thirty-two foodborne bacterial isolates were tested as potential competitors of Listeria monocytogenes strain LM82 during enrichment because of their resistance to the selective agents in Listeria enrichment and isolation media. Competitive ability of each isolate was classified as weak, moderate, or strong by determining the ratio at which it masked identification of LM82 at an inoculation concentration of 10 colony forming units (CFU)/10 mL of Listeria enrichment broth. Of the competitive isolates identified, six were Enterococcus spp., two were Staphylococcus spp., and one was a Corynebacterium sp. Although several strains of Enterococcus faecium were examined, not all were competitive. Of six other bacterial strains associated with food fermentations and tested for competitiveness with LM82, one, a Gram-positive tetrad, was competitive. This study showed that although food microfloral strains that are able to survive in enrichment and isolation environments are fairly common, they do not necessarily compete with Listeria. Not all strains in a competitive species are necessarily competitive.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    Journal of food safety 16 (1996), S. 0 
    ISSN: 1745-4565
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Extracellular antimicrobial substances produced by certain enterococci inhibit Listeria monocytogenes. Enterococcus faecium 108, a competitive food isolate, produced a heat-stable and protease-sensitive anti-L. monocytogenes bacteriocin-like substance (Ef108) in Listeria selective enrichment broth and other media. Ef108 activity was purified to homogeneity by a four-step procedure including (NH4)2SO4 fractionation, chromatography on anion exchange QSepharose column, and two Superose 12 gel filtration columns. In activities represented by two peaks (Ef108A and Ef108B), 90% of the crude activity was due to peak B. Ef108A is believed to be a variable aggregate of the active moiety in Ef108B. All Listeria spp. and five L. monocytogenes serotypes were inhibited by Ef108B in several media including Listeria enrichment medium. The Ef108 activity may be due to a bacteriocin-like inhibitory substance produced by E. faecium 108 that may suppress the growth and predominance of Listeria monocytogenes during selective enrichment.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Journal of industrial microbiology and biotechnology 13 (1994), S. 389-391 
    ISSN: 1476-5535
    Keywords: Shared-use cosmetics ; Cosmetic test kits ; Microbial survey
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Process Engineering, Biotechnology, Nutrition Technology
    Notes: Summary Some people like to try cosmetics before purchasing them. With repeated use by different customers, however, the tester kits provided by many retail outlets can become potential vectors of microbial pathogens. A survey was conducted to assess the health risk from bacteria found on shared-use cosmetics. A total of 3027 shared-use cosmetic product samples were collected from 171 retail establishments throughout the contiguous United States. Eye, face and lip cosmetics were tested within situ nondestructive swabbing and the use of the Transette 3R Modified Amies Charcoal Culture and Transport System. Bacteria were isolated from about 50% of the items for all three categories. Semiquantitatively-estimated mean densities were 2288, 1685 and 1088 CFU g−1 for eye, face and lip products, respectively. Ranges for all categories were 0–155 CFU g−1. About 5% of the items had bacterial counts above 5000 CFU g−1 (eye products) or 10 000 CFU g−1 (other products). More than 60% of isolates were typical of microflora from human skin; the remainder were environmental microbes. About 60% of the isolates were Gram-positive cocci:Staphylococcus spp. (especiallyS. epidermidis) andMicrococcus spp. The Gram-negative pathogenPseudomonas aeruginosa constituted 0.07% of the isolates. The survey results suggest that the preservation systems of some of the cosmetics failed under excessive use (abuse), and indicated a potential for microbiological safety problems with shared-use consmetics.
    Type of Medium: Electronic Resource
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