Proposal to validate <i>Listeria swaminathanii</i> sp. nov. and reassign the type strain to UTK S2-0008

ABSTRACT Listeria swaminathanii UTK S2-0008, isolated from soil collected in the Nantahala National Forest in North Carolina, USA, is the only L. swaminathanii strain eligible to serve as the type strain, which is needed to achieve valid status. The previously effectively published type, L. swaminathanii FSL L7-0020 T , and previously described strains UTK C1-0015 and UTK C1-0024 do not conform to the International Code of Nomenclature of Prokaryotes’ rules for type strains. Additionally, the currently designated type strain (FSL L7-0020 T = ATCC TSD-239 T ) is an atypical representative of L. swaminathanii as it is the only strain lacking catalase activity. Therefore, it is proposed to reassign the type to L. swaminathanii (UTK S2-0008 T = CCUG 77280 T = LMG 33255 T ). Whole-genome sequence-based average nucleotide identity (ANI) showed that this strain clustered with the three previously described L. swaminathanii strains (FSL L7−0020 = ATCC TSD-239, UTK C1-0015, and UTK C1-0024; pairwise ANI ranged from 98.71% to 98.83%). All four strains, including the one described here, could not be classified as any validly published Listeria species and showed the highest similarity to Listeria marthii (maximum ANI of 93.92%, in silico DNA-DNA hybridization of 56.2%). L. swaminathanii exhibits the phenotypic characteristics that are currently expected of the Listeria sensu stricto species. This species lacks phenotypic characteristics associated with Listeria pathogenicity (non-hemolytic and negative for phosphatidylinositol-specific phospholipase C activity); the genomes lack genes associated with virulence (all genes found on the Listeria pathogenicity island 1 [LIPI-1], as well as the internalin genes inlA and inlB ), which support L. swaminathanii is nonpathogenic. IMPORTANCE The genus Listeria includes species of significant relevance to food safety, environmental microbiology, and public health. Accurate species identification is critical because misidentification of nonpathogenic species as pathogenic ones can lead to unnecessary recalls and regulatory complications. The validation of Listeria swaminathanii sp. nov. will ensure that this species is formally recognized and has a type strain (UTK S2-0008 T ) that is representative of the species. This work strengthens diagnostic accuracy by enabling the inclusion of this species in reference databases and inclusivity studies, reducing the risk of false identification. Furthermore, the identification and characterization of Listeria swaminathanii sp. nov. expands our understanding of the genetic and ecological diversity within the genus Listeria , particularly among soil-dwelling strains.