Gas gangrene, a subset of necrotizing soft tissue infections, is a surgical emergency characterized by rapid clinical progression and high mortality rates. Traditionally, Clostridium perfringens has been recognized as the primary causative agent; however, “nonclostridial gas gangrene” is increasingly being reported, particularly in patients with predisposing conditions such as diabetes mellitus, peripheral vascular disease, and immunosuppression [1,2]. Nonclostridial gas gangrene is often polymicrobial, involving a synergistic interaction between aerobic and anaerobic bacteria [3]. Among these, the Streptococcus anginosus group—comprising S. anginosus, S. constellatus, and S. intermedius—is known for its pyogenic potential and tendency to form localized abscesses [4]. While S. anginosus is a common commensal of the gastrointestinal and urogenital tracts, its involvement in extensive, gas-forming necrotizing infections of the lower extremity is exceptionally rare. The management of such infections in the diabetic foot is 2-fold: first, the urgent control of the life-threatening infection through radical debridement, and second, the management of the resulting complex wound to prevent major limb amputation. In this report, we present a rare case of nonclostridial gas gangrene caused by S. anginosus in a patient with uncontrolled diabetes and describe the successful outcome through emergency debridement followed by microsurgical reconstruction. This study was approved by the Institutional Review Board of the Konkuk University Hospital (IRB No. 2026-02-022). Written informed consent was obtained from the patient for the publication of this case report and any accompanying images.

A 48-year-old female patient with a history of diabetes mellitus for over 10 years presented to our institution. She had discontinued her antidiabetic medication for 2 weeks and had ceased regular medical follow-up. Three weeks prior to admission, she sustained a foot injury and managed it with self-disinfection and simple dressings at a local clinic. However, her symptoms progressively worsened, leading to her presentation at our institution (Fig. 1).

Upon admission, laboratory investigations revealed a high-sensitivity C-reactive protein (hs-CRP) level of 27.07 mg/dL (reference range: 0.01–0.3 mg/dL), hemoglobin A1c (HbA1c; National Glycohemoglobin Standardization Program) of 9.0% (reference range: 4.3%–5.6%), a white blood cell (WBC) count of 22,610/µL, and a serum glucose level of 409 mg/dL. Foot X-rays taken on admission demonstrated osteolysis of the right 5th proximal phalanx and the 4th and 5th metatarsal heads, along with soft tissue emphysema (Fig. 2).

The patient had no prior history of foot disease other than diabetes, indicating that the osteolysis observed on the X-ray was primarily due to the acute infection rather than pre-existing chronic osteomyelitis. Due to the urgent need for emergent surgical intervention to control the rapidly progressing, life-threatening infection, preoperative computed tomography or magnetic resonance imaging was omitted.

Upon admission, a preliminary wound culture was obtained using a swab from the deep wound bed. Given the rapid progression and extensive gas formation in a patient with uncontrolled diabetes, a severe polymicrobial necrotizing soft tissue infection was primarily suspected rather than an isolated clostridial infection. Consequently, emergency surgery was immediately performed, involving extensive debridement ranging from the plantar to the dorsal aspect of the foot, along with amputation of the fifth toe (Fig. 3). During the procedure, deep tissue and bone specimens were additionally obtained for accurate culture. To broadly cover both aerobic and anaerobic pathogens typical of complex diabetic foot infections, empiric intravenous antibiotic therapy with ampicillin/sulbactam (3 g, four times daily) was initiated.

Four days postoperatively, the initial swab culture, as well as subsequent tissue and bone cultures obtained during the debridement, confirmed a heavy growth of S. anginosus and a light growth of Streptococcus agalactiae. All cultures demonstrated susceptibility to ampicillin/sulbactam. Follow-up laboratory tests indicated significant improvement, with an hs-CRP of 3.29 mg/dL, WBC of 7,250/μL, and serum glucose of 167 mg/dL (Fig. 4).

The patient was continuously maintained on intravenous ampicillin/sulbactam (3 g, four times daily) until early soft tissue coverage was deemed safe and necessary due to the exposure of tendons and bone. Conventional angiography confirmed vascular patency (Fig. 5). On hospital day 13, we performed a free flap reconstruction using a thoracodorsal artery perforator (TDAP) free flap, utilizing the posterior tibial artery as the recipient vessel (Fig. 6). The ampicillin/sulbactam regimen was maintained until 3 days after free flap coverage. However, as pneumonia was detected on postoperative day 3 following flap surgery, the antibiotic regimen was switched to intravenous piperacillin/tazobactam (4.5 g, four times daily) and maintained until the pneumonia resolved.

At the 4-month follow-up, the patient exhibited complete wound healing. Mild plantar bulging of the flap was noted; however, the patient was instructed to minimize prolonged walking to prevent callus formation or pressure injuries, rather than utilizing specialized footwear or orthotics. Her HbA1c had decreased to 6.2%, indicating well-controlled blood glucose levels achieved through the combination of successful local wound coverage and systemic multidisciplinary medical management (Fig. 7).

This report highlights the clinical significance of nonclostridial gas gangrene, an entity that must be carefully differentiated from classic clostridial infections. While typical risk factors include trauma, surgery, malignancy, and alcoholism, uncontrolled diabetes mellitus remains a critical predisposing factor [5]. Unlike clostridial infections, nonclostridial cases are typically characterized as polymicrobial infections involving a synergy between aerobic and anaerobic bacteria [1,3].

In this case, differentiating nonclostridial from clostridial gangrene solely based on clinical presentation was exceptionally difficult initially due to the similar rapid progression and soft tissue emphysema. The causative organisms were confirmed 4 days after the initial wound culture. The isolation of S. anginosus alongside S. agalactiae suggests a profound synergistic effect in the hyperglycemic and hypoxic environment of the diabetic foot. This pathophysiological mechanism facilitates rapid gas production and extensive tissue necrosis [4,6].

The management of nonclostridial gas gangrene differs from classic clostridial infections in several critical ways, dictating a specific surgical approach. Clostridial myonecrosis frequently requires hyperbaric oxygen therapy and often mandates high-level major amputations due to irreversible and extensive muscle necrosis [1,3]. In contrast, nonclostridial infections driven by the S. anginosus group have a distinct pyogenic nature, tending to form insidious abscesses that track along fascial planes [4,6]. Therefore, the primary surgical principle for successful limb salvage in this context is the meticulous exploration of hidden abscess pockets and the radical excision of infected fascia and necrotic tissue, rather than aggressive prophylactic muscle resection [3,5].

In our case, identifying the nonclostridial etiology fundamentally reinforced our limb salvage strategy. Fortunately, the empiric ampicillin/sulbactam effectively covered the isolated pathogens, requiring no change in the antibiotic regimen [5]. However, confirming that the infection was nonclostridial provided crucial clinical confidence that the aggressive local infection could be contained without resorting to a major amputation. Once the infection was clinically stabilized through meticulous debridement and culture-directed targeted antibiotic therapy, we were able to safely proceed with delayed microsurgical reconstruction. Utilizing a TDAP free flap not only provided durable coverage for the exposed bone and tendons but also brought well-vascularized tissue to the compromised diabetic wound bed, significantly promoting local wound healing. This successful local control, in conjunction with multidisciplinary systemic medical care, ultimately contributed to optimal glycemic control and prevented major limb amputation [7,8].