This 1974 study reexamines the taxonomy of Listeria using both classical phenotypic characteristics and DNA-DNA hybridization. Researchers analyzed 70 phenotypic characters of Listeria monocytogenes and compared them with various other bacterial species, finding that Listeria most closely resembled streptococci, Staphylococcus aureus, and Diplococcus pneumoniae. DNA hybridization studies, however, revealed minimal genetic relatedness between Listeria and other bacterial families including Corynebacteriaceae, Micrococcaceae, and Lactobacillaceae. The DNA base composition data showed that L. monocytogenes, L. grayi, and L. murrayi form a homogeneous group, while L. denitrificans differed significantly. Based on these molecular findings and previous hybridization studies, the authors recommend transferring the avirulent species L. grayi and L. murrayi to a new genus, Murraya, as M. grayi and M. grayi subsp. murrayi. They also propose establishing a new family, Listeriaceae, to accommodate both Listeria and Murraya genera.

Key findings

• L. monocytogenes showed phenotypic similarity to streptococci, Staphylococcus aureus, and Diplococcus pneumoniae, but DNA-DNA hybridization revealed no significant genetic relatedness to these or other tested organisms
• DNA-DNA hybridization demonstrated that L. grayi and L. murrayi form a distinct genetic group sharing 60-70% sequence homology with each other but only 20-40% with L. monocytogenes
• L. denitrificans differed from other Listeria species by 16% in GC content, suggesting it may represent a distinct lineage
• The authors propose transferring L. grayi and L. murrayi to a new genus Murraya and establishing a new family Listeriaceae to properly reflect molecular relationships