[Distribution of species of the genus Listeria]

Abstract

Within the classification of different Listeria species according to present knowledge, this study investigates the sources and distribution of both the known "classical" species of Listeria as well as the recently added species: L. monocytogenes, L. innocua, L. ivanovii, L. welshimeri, L. seeligeri, L. grayi and L. murrayi. For this purpose 573 isolates from the environment, food, healthy carriers and patients suffering from listeriosis were selected out of a total of approximately 6000 strains originating from all parts of the globe which are maintained at the Listeria Culture Collection of the Institute of Hygiene, Würzburg. The selection was made according to the criterium of widest possible geographic distribution. The results indicate the environment to be the natural reservoir of all of the 7 'new' Listeria species. Healthy animal carriers harbour in their intestinal tract all species of Listeria with the exception of L. murrayi, whilst in the excreta of healthy individuals only the species L. monocytogenes, L. ivanovii, and L. innocua were found. Identification of strains from pathological specimens of human and animal origin resulted invariably in the finding of L. monocytogenes or L. ivanovii. L. grayi (7 strains) was found sporadically in Europe and in the USA, whereas L. murrayi (9 strains) has been isolated only in the USA. 26 of 28 so far known strains of L. welshimeri originated from the USA, and only 2 strains of this species were found in Europe. L. seeligeri (80 strains) was identified among European isolates, L. innocua, however, in both USA and Europe. L. ivanovii occurs in Australia, Europe and the USA. L. monocytogenes is of global distribution. Table 1 presents a survey of species, serovariety and origin of the 573 isolates. As both pathogenic and non pathogenic listeria strains are found in the human environment, it is necessary to identify each isolate appropriately, particularly in view of the elucidation of the rather obscure epidemiology of human listeriosis.