Microbiology of Actinomyces Species Isolated From Patients With Invasive Disease and Contaminated Samples in a Comprehensive Cancer Center.

Background: Actinomyces are mucous membrane commensals that infrequently cause invasive disease. Our goal was to define Actinomyces species prevalence, the predominant disease site and risk factors for actinomycosis.

Methods: We retrospectively reviewed patients with growth of Actinomyces species from cultures in a single-cancer center from July 2007 to June 2020. Proven invasive actinomycosis was defined as the presence of compatible clinical syndrome and radiographic findings with histopathological confirmation or culture from a normally sterile site. Probable invasive actinomycosis was defined based on the same criteria but without histologic confirmation. Contaminants were defined as culture growth in the absence of clinical or radiological findings consistent with disease. Speciation of Actinomyces was performed by the bioMerieux VITEK 2 anaerobic and coryneform identification card.

Results: Of 235 patients, 179 (76.2%) had malignancy. Among 90 (38.3%) patients with invasive actinomycosis, A odontolyticus was isolated in 32 (35.6%), followed by A meyeri in 20 (22.2%), and A naeslundii in 17 (18.9%). Among 145 (61.7%) colonized patients, A odontolyticus was isolated in 67 (46.2%), followed by A naeslundii in 27 (18.6%). Abdominopelvic infection was the most common site for invasive actinomycosis documented in 54 patients (60.0%) followed by orocervicofacial in 14 (15.6%) and thoracic in 10 (11.1%).

Conclusions: A odontolyticus, A meyeri, and A naeslundi were the most frequently isolated species causing invasive actinomycosis, and A odontolyticus and A nauslendii among colonizers. Abdominopelvic represented the most frequent site for invasive disease. Further studies are needed to investigate the epidemiology of Actinomyces species in this population.