Significance, clinical spectrum, and microbiological evaluation of Actinomyces blood stream infections

Actinomyces species are Gram-positive anaerobic bacilli that are commensal in the gastrointestinal and genital tracts. Actinomyces blood stream infections (BSIs) are rare but becoming more frequent with advanced diagnostic techniques. The presented study aims to evaluate relevance, clinical and microbiological spectrum of Actinomyces species bacteremia.

A retrospective cohort study was conducted for all reported Actinomyces species BSI between January 2016 to November 2020. Isolates identification and antimicrobial susceptibility tests were performed using matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and BD PhoenixTM automated systems.

Overall, 37 episodes of Actinomyces BSIs were recorded, most were Actinomyces odontolyticus (40.5%, 15/37). The mean age of patients was 32 years, with females' preponderance (23/37, 62.2%). Cultures were considered significant in only 48.6% cases (18/37), in which the primary source of infection was attributed to oropharyngeal origin (40%) with excellent activity for amoxicillin and ceftriaxone but poor susceptibility to aminoglycosides and quinolines. Of those who received antimicrobials (87.5%, 28/32), shorter duration of therapy (<2 weeks) did not result in long-term consequences with 86.5% 1-year survival rate.

Nearly half of the cases were deemed clinically insignificant and responded well to short courses of antimicrobial therapy without long-term consequences. Penicillin and cephalosporins demonstrated superior activity compared to aminoglycosides and quinolones.