Mixed Actinomycotic-Pyogenic Liver Abscess With Penicillin-Intermediate, Clindamycin-Resistant Actinomyces odontolyticus Bacteremia: A Case Report

Hepatic actinomycosis is an uncommon diagnostic mimic of pyogenic or amoebic liver abscess. A 34-year-old healthy man presented with fever, vomiting, and right upper quadrant pain after recent travel. Computed tomography showed a 7 x 7 x 5 cm subcapsular segment VIII hepatic abscess. Empirical piperacillin-tazobactam and metronidazole were started, followed by ultrasound-guided drainage with catheter placement. Blood cultures grew Actinomyces odontolyticus, and the abscess aspirate grew Streptococcus intermedius, supporting a mixed actinomycotic-pyogenic abscess rather than incidental bacteremia. Low-titer Entamoeba histolytica serology was not considered clinically significant. The Actinomyces isolate showed intermediate susceptibility to penicillin and resistance to clindamycin. After a partial response to amoxicillin-clavulanate, therapy was changed to doxycycline with serial ultrasound surveillance showing interval cavity regression. The case emphasizes contextual interpretation of Actinomyces bacteremia, early source control, and susceptibility-guided prolonged therapy.