Diversity of Listeria Species in Urban and Natural Environments

A total of 442Listeria isolates, including 234Listeria seeligeri , 80L. monocytogenes , 74L. welshimeri , 50L. innocua , and 4L. marthii isolates, were obtained from 1,805 soil, water, and other environmental samples collected over 2 years from four urban areas and four areas representing natural environments.Listeria spp. showed similar prevalences in samples from natural (23.4%) and urban (22.3%) environments. WhileL. seeligeri andL. welshimeri were significantly associated with natural environments (P ≤ 0.0001),L. innocua andL. monocytogenes were significantly associated with urban environments (P ≤ 0.0001). Sequencing ofsigB for all isolates revealed 67 allelic types with a higher level of allelic diversity among isolates from urban environments. SomeListeria spp. andsigB allelic types showed significant associations with specific urban and natural areas. Nearest-neighbor analyses also showed that certainListeria spp. andsigB allelic types were spatially clustered within both natural and urban environments, and there was evidence that these species and allelic types persisted over time in specific areas. Our data show that members of the genusListeria not only are common in urban and natural environments but also show species- and subtype-specific associations with different environments and areas. This indicates thatListeria species and subtypes within these species may show distinct ecological preferences, which suggests (i) that molecular source-tracking approaches can be developed forListeria and (ii) that detection of someListeria species may not be a good indicator forL. monocytogenes .