Schaalia odontolytica

Abstract

Schaalia is a newly established bacterial genus created following genome-based taxonomic reclassification of species previously belonging to Actinomyces. Schaalia odontolytica (formerly Actinomyces odontolyticus) is a pleomorphic, Gram-positive bacillus that grows under aerobic or microaerophilic conditions, forming small, whitish colonies that develop a dark-red pigment after several days. It is catalase- and oxidase-negative and non-motile.

This microorganism is part of the normal microbiota of the oral cavity, gastrointestinal tract, and genitourinary tract, but it can cause infections in cervicofacial, thoracic, abdominal, and pelvic regions. Such infections may involve the skin, bones, joints, respiratory tract, or genitourinary tract and are often associated with abscess and fistula formation, although bacteremia is uncommon. Its clinical presentation is similar to infections caused by Actinomyces israelii and related species.

Diagnosis is primarily performed using MALDI-TOF, and PCR or 16S rRNA gene sequencing may be required. There is no standardized method for antimicrobial susceptibility testing, but S. odontolytica is generally susceptible to penicillin, amoxicillin, ceftriaxone, and carbapenems, as well as vancomycin, tigecycline, and rifampicin. It typically shows resistance to aminoglycosides, metronidazole, trimethoprim-sulfamethoxazole, cloxacillin, first-generation cephalosporins, aztreonam, ceftazidime, and fluoroquinolones.