Comamonas kerstersii and the Perforated Appendix

LETTER

We read with interest two recent reports of Comamonas kerstersii-related infections in the abdomen (1) and bloodstream (2). We wish to add our own experience with C. kerstersii-related abdominal infections.

Case 1.

A 10-year-old boy presented with a 1-day history of abdominal pain. Examination revealed peritonitis in the right iliac fossa. On admission, his white blood cell count was 10.3 ×10⁹/liter and his C-reactive protein level was 228 mg/liter. A diagnosis of appendicitis was made, and an open appendectomy revealed a perforated appendix. Microscopic examination of peritoneal pus showed small numbers of Gram-negative bacilli that were plated onto Columbia blood agar (Oxoid), chocolate agar (Oxoid), and fastidious anaerobic agar with blood (Oxoid). After 48 h of incubation at 36°C in ambient air, colonies on the blood agar plate were identified by matrix-assisted laser desorption ionization–time of flight (MALDI-TOF) mass spectrometry (Bruker) as C. kerstersii and a fine growth on the anaerobic plate was identified by MALDI-TOF as Streptococcus constellatus. These were the only organisms isolated. Postoperatively, the patient received piperacillin-tazobactam for 5 days and was discharged on amoxicillin-clavulanic acid and ciprofloxacin, making a full recovery.

Case 2.

A 9-year-old boy presented with a 3-day history of right-sided constant abdominal pain associated with pyrexia. Examination revealed a tender right iliac fossa with localized peritonitis. On admission, his white blood cell count was measured at 13.6 ×10⁹/liter and his C-reactive protein level was 65 mg/liter. He developed septic shock and underwent emergency surgery, during which a perforated appendix was resected. Microscopic analysis of intraoperative peritoneal pus and an operative swab of the perforated appendix showed numerous pus cells but no organisms. After 48 h of incubation (as detailed above), the peritoneal fluid grew S. constellatus, Bacteroides fragilis, and C. kerstersii, as identified by MALDI-TOF, and the appendix swab revealed a pure growth of C. kerstersii. The patient received 3 days of intravenous amoxicillin-clavulanic acid, gentamicin, and metronidazole and was discharged on oral amoxicillin-clavulanic acid. He made a full recovery.

C. kerstersii, which has undergone extensive reclassification (3, 4), was isolated from our patients as part of a polymicrobial growth from peritoneal fluid. MALDI-TOF appeared to be a reliable tool for identifying these organisms. In case 1, C. kerstersii was identified with a score of 2.275, followed by Comamonas testosteroni (1.664) and Comamonas aquatica (1.579), and in case two, C. kerstersii was identified with a score of 2.294, followed by C. aquatica (1.585), Brenneria nigrifluens (1.299), and C. testosteroni (1.222). The antibiotic sensitivities of the isolates obtained are shown in Table 1. In addition, disc diffusion testing of the isolate from case 2 for amoxicillin-clavulanic acid showed a large zone of >25 mm, suggesting sensitivity, and the use of amoxicillin-clavulanic acid resulted in a good clinical outcome.

TABLE 1.

Sensitivity patterns of C. kerstersii isolates

Isolate source	Sensitivitya to:
	Amikacin	Ceftazidime	Ciprofloxacin	Colistin	Gentamicin	Meropenem	Piperacillin-tazobactam	Amoxicillin-clavulanic acid
Case 1	S	S	S	S	S	S	S	NTb
Case 2	S	S	R	S	S	S	S	S

^aDetermined by disc diffusion (5). S, sensitive; R, resistant.

^bNT, not tested.

Finally, Opota et al. have suggested translocation of Comamonas from the gut as the source of infections. Within our hospital, over a period of 2 years, pure growth of C. kerstersii was isolated from 27 fecal samples sent for investigation of diarrhea, all with MALDI-TOF scores of >2.0. We hypothesize that environmental exposure leading to carriage within the bowel may be more common than currently assumed.