The rising tide of bloodstream infections with Actinomyces species: bimicrobial infection with Actinomyces odontolyticus and Escherichia coli in an intravenous drug user.

Clinicians of all specialties need to be aware of a recent, nationwide increase in the number of Actinomyces bloodstream infections. We report a case of bimicrobial bloodstream infection with Actinomyces odontolyticus and Escherichia coli in an intravenous drug user. A 36-year-old, male intravenous drug user was admitted with acute-onset pleuritic chest pain, back pain, pyrexia, tachycardia, tachypnoea and hypotension. Chest CT showed multiple, bilateral, cavitating lung lesions, most likely the result of septic emboli originating from an infected deep venous thrombosis (DVT). Blood cultures led to a mixed growth of A. odontolyticus, identified by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF), and E. coli. The rising tide of bloodstream infections with Actinomyces species is likely to continue with the increasing availability of sophisticated molecular identification techniques, including MALDI-TOF. In this case, the results of antimicrobial susceptibility tests were particularly important because the E. coli was susceptible to ciprofloxacin, whereas the A. odontolyticus was resistant.