Polymicrobial infections with specific and related organisms, using the current taxonomy.

organisms reside on mucosal surfaces of the oropharynx and the genitourinary tract. Polymicrobial infections with organisms are increasingly being reported in the literature. Since these infections differ from classical actinomycosis, lacking of specific clinical and imaging findings, slow-growing organisms can be regarded as contaminants or insignificant findings. In addition, only limited knowledge is available about novel species and their clinical relevance. The recent reclassifications have resulted in the transfer of several species to novel genera , , , , or . The spectrum of diseases associated with specific members of and these related genera varies. In human infections, the most common species are Actinomyces , , and , which are typical inhabitants of the mouth, and , , and . In this narrative review, the purpose was to gather information on the emerging role of specific organisms within the and related genera in polymicrobial infections. These include in pulmonary infections, in brain abscesses and infections in the lower respiratory tract, in skin-related infections, in necrotizing fasciitis and skin abscesses, and in infected tissues around prostheses and devices. Increased understanding of the role of and related species in polymicrobial infections could provide improved outcomes for patient care. Key messages Due to the reclassification of the genus, many former species belong to novel genera , , , , or .Some of the species play emerging roles in specific infection types in humans.Increasing awareness of their clinical relevance as an established or a putative pathogen in polymicrobial infections brings about improved outcomes for patient care.