Are all strains of Listeria monocytogenes equally pathogenic (virulent)? The simple answer to this is, yes, all strains are considered equally virulent. There are a number of different genes in L. monocytogenes that cause it to be pathogenic, including genes for listeriolysin S, internalin A, listeriolysin O, phospholipase and invasion associated protein. Not all strains have all the genes and different strains can cause disease even if they don’t have all the genes. Currently, there is no test to show complete correlation between gene presence/absence and pathogenicity, so all strains are considered equally pathogenic.
The listeria protein internalin A mediates bacterial adhesion and invasion of epithelial cells in the human intestine through specific interaction with its host cell receptor E-cadherin. Many strains of L. monocytogenes have been shown to produce a truncated (inactive) internalin A. However, some strains that have caused disease have truncated internalin A.
In the future, it may be possible to assign a different risk profile to different strains based on their gene complement, but for now, all strains are considered equally pathogenic.
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