The microorganisms that most frequently cause skin abscesses are S. aureus and S. pyogenes. However, anaerobic bacteria are also a common aetiology in wound-associated infections.1 Among them, the Clostridium genus is particularly important, as its spores can infect wounds and open fractures, with C. perfringens, C. histolyticum, C. novyi and C. septicum being the most common. Here we present a case of an upper extremity abscess due to an unusual species of Clostridium.
A 5-year-old girl, fully vaccinated and with no relevant medical history, suffered an injury after impaling it on a piece of wood while playing in the park. In paediatric Accident and Emergency, she was given a dose of IV amoxicillin and the fragment was removed without apparent complications, so she was discharged with a one-week course of oral cefadroxil. However, check-up of the wound a week later showed the patient had developed cellulitis and spontaneous drainage from a purulent-looking collection. It was decided to admit her to paediatric surgery, she was prescribed IV amoxicillin-clavulanic acid therapy, and a microbiological study of the collection was requested. On day three of admission, Ultrasound-Doppler detected a 2.5 cm residual fragment of wood in the patient’s elbow, so surgery was scheduled to remove it. During surgery, the fragment was removed, lavages performed with vancomycin, hydrogen peroxide and Betadine®, and the wound was closed. On day six of admission, the antibiotic therapy was discontinued and the patient was discharged due to the good appearance of the wound. Paediatric orthopaedics carried out weekly outpatient check-ups, and the patient was definitively discharged at the third check-up due to resolution of the condition.
On arrival at the laboratory, the skin abscess sample was cultured under aerobic and anaerobic conditions. At 48 h, the aerobic culture was negative, while in the blood agar medium for anaerobes (Wilkins Chalgrens®) supplemented with amikacin, there was scant growth of flat, transparent colonies with irregular edges and slightly β-haemolytic. Using MALDI-TOF (Bruker®), the microorganism was identified as C. subterminale with a score of 1.9, but not unanimously. The definitive identification was carried out by detection of the 16S rRNA gene using real-time PCR and subsequent Sanger sequencing of the fragment. After comparing the sequence obtained in the Basic Local Alignment Search Tool (BLAST) NCBI database, the identification of C. subterminale was confirmed. Antibiotic sensitivity was determined by E-test as described in the corresponding section of Sociedad Española de Enfermedades Infecciosas y Microbiología Clínica (SEIMC) [Spanish Society of Infectious Diseases and Clinical Microbiology] procedure 11. The EUCAST 2023 breakpoints for C. perfringens were followed, as shown in Table 1.
Susceptibility study of C. subterminale using E-test.
| Antibiotic | MIC (mg/l) | Status |
|---|---|---|
| Penicillin | 0.032 | Sensitive |
| Amoxicillin/clavulanic acid | ≤ 0.016 | Sensitive |
| Piperacillin/tazobactam | 0.064 | Sensitive |
| Cefoxitin | 1 | — |
| Meropenem | 0.006 | Sensitive |
| Clindamycin | 0.094 | Sensitive |
| Moxifloxacin | 0.19 | — |
| Metronidazole | 0.032 | Sensitive |
C. subterminale is a saprophytic soil bacterium, closely related to C. botulinum group IV, which has been occasionally associated with skin and soft tissue infection,2,3 pleuropulmonary infection2,4 and bacteraemia,5–7 and the production of botulinum toxin type A has also been reported.8 A 2022 literature review9 suggests that C. subterminale infection primarily affects patients with underlying disease and immunosuppressed patients. In terms of treatment, drainage or surgical debridement was essential in all cases, and, although antibiotics were administered in each case, an antibiogram was only available for two of the 14 patients.
Here we present a case of C. subterminale infection in a wound caused by a wood fragment in a 5-year-old immunocompetent girl with no other medical history. The patient was initially treated with cefadroxil (unlikely activity) and subsequently with amoxicillin-clavulanic acid (sensitive). However, this case did not resolve until the abscess was drained. We believe that further studies are necessary to evaluate whether antibiotic therapy provides additional benefit to drainage in these infections and, if so, which antibiotic is the most appropriate. This case reinforces the need to consider C. subterminale as a cause of infections, even in healthy paediatric patients, and assess the utility of anaerobic culture of abscesses, and to confirm identification at the species level by molecular biology.
