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The overgrowth of Listeria monocytogenes by other Listeria spp. in food samples undergoing enrichment cultivation has a nutritional basis. | LitMetric

The overgrowth of Listeria monocytogenes by other Listeria spp. in food samples undergoing enrichment cultivation has a nutritional basis.

Int J Food Microbiol

Agence Française de Sécurité Sanitaire des Aliments Laboratoire d'Etudes et de Recherches sur la Qualité des Aliments et sur les Procédés Agro-Alimentaires, Afssa, 23 Avenue du Général de Gaulle, 94706 Maisons Alfort Cedex, France.

Published: January 2010

AI Article Synopsis

  • - The isolation of Listeria monocytogenes from food often faces challenges due to its potential overgrowth by other Listeria species during double enrichment, which can lead to false negatives in testing.
  • - Experimental analysis revealed that L. monocytogenes can be outgrown by Listeria innocua during the late exponential growth phase due to interactions, while a dominant L. monocytogenes strain can also suppress Listeria welshimeri’s growth rate.
  • - Despite testing various factors in the ISO 11290-1 methodology, no single determinant was found for the overgrowth, but adding agar to the broth significantly reduced overgrowth in mixed strain experiments, indicating competition for nutrients plays a key role

Article Abstract

The isolation of Listeria monocytogenes from food is carried out using a double enrichment. In cases where multiple Listeria species are present within the original sample, L. monocytogenes can be overgrown during enrichment by other species of listeria present in the original sample. From a practical perspective, this can result in a false negative or complicate the ability of public health investigators to match food and clinical isolates. We have further investigated this phenomenon by analysing the growth kinetics of single species and pairs of different species over the ISO 11290-1 enrichment process. The overgrowth of a strain of L. monocytogenes by a strain of Listeria innocua resulted primarily from interactions which occurred in late exponential phase, where it was observed that growth of both strains stopped when the dominant strain reached stationary phase. In a second mixed culture, the dominant L. monocytogenes strain suppressed the exponential growth rate of the second Listeria welshimeri strain. Both findings suggest that the overgrowth could partially be explained in terms of a nutritional competition. Multi-factor analysis of Fraser broth constituents and growth temperatures using both stressed and non-stressed inoculants failed to identify any single factor in the ISO 11290-1 methodology which would contribute to the overgrowth phenomenon in our model system. Furthermore, species was not a significant factor in observed differences in growth parameters among a wider array of strains which had been stressed or not stressed prior to grown in Fraser broths, even though some strains had significantly faster growth rates than others. Limiting diffusion in Fraser broth through the addition of agar significantly reduced the extent of the overgrowth in experiments using mixtures of strains originally isolated from foods where overgrowth had been previously observed. Taken together, these findings support that the overgrowth phenomenon in most instances has a nutritional basis.

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Source
http://dx.doi.org/10.1016/j.ijfoodmicro.2009.10.025DOI Listing

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