Actinotignum schaalii infection - a case series from a tertiary hospital in Greece.

Introduction: Actinotignum schaalii is a small Gram-positive facultative anaerobic coccoid rod that was reclassified in 1997 from the genus Actinomyces and is difficult to culture with usual microbiological techniques, as it is slowly growing. A. schaalii is an emerging human pathogen that is most commonly implicated in urinary tract infections (UTIs), but has also been isolated less frequently from abscesses of various sites (such as the skin, the genitourinary tract, surgical sites or intraabdominal).

Methods: All cases where A. schaalii was identified during a 6-year period (January 2016 - January 2022) in the University Hospital of Heraklion were reviewed.

Results: A. schaalii was isolated in 11 cultures from 10 patients. The site of infection was skin and soft tissue in nine out of eleven cultures (81.8%) and the bone was the site of infection in two patients (18.2%). Most cultures were polymicrobial. The median age of patients was 55.5 years (interquartile range 34-63 years), and 80% (n=8) were male. A. schaalii was susceptible to beta-lactams, quinolones and vancomycin, but resistant to clindamycin, erythromycin and metronidazole. Moreover, two cases of diabetic patients diagnosed with polymicrobial diabetic foot osteomyelitis from this organism are presented in detail. Both patients were successfully managed with targeted antimicrobial treatment and prompt surgical management.

Conclusions: A. schaalii is an emerging pathogen that is likely under-reported due to difficulties in isolation and identification. Herein two cases of diabetic foot osteomyelitis are also presented in detail, successfully managed with targeted antimicrobial therapy and surgical debridement.