Rationale: Comamonas species are rarely associated with human infections. Recent reports found that Comamonas kerstersii was associated with severe diseases such as abdominal infection and bacteremia. However, C. kerstersii maybe be confused with Comamonas testosteroni using the automatic bacterial identification systems currently available.
Patient concerns: A 31-year-old man who had onset of left upper abdominal pain developed clinical manifestations of right lower abdominal pain and classic migration of pain at the temperature of 39°C. The positive strain of aerobic and anaerobic bottles of blood cultures was identified.
Diagnoses: The patient was diagnosed as acute peritonitis and perforated appendix with abdominal abscess.
Interventions: The bacterium was identified by routine methods, MALDI-TOF-MS and PCR amplification of the 16S rRNA. The patient was treated with exploratory laparotomy, appendectomy, tube drainage, and prescribing antibiotic treatment.
Outcomes: The patients were discharged with complete recovery. The organisms were confirmed as C. kerstersii by MALDI-TOF-MS and a combination of the other results.
Lessons: Our findings suggest that C. kerstersii infection occurs most often in association with perforated appendix and bacteremia. We presume that C. kerstersii is an opportunistic pathogen or commensal with the digestive tract and appendix bacteria.