Rare Pathogen in Diabetic Foot Gangrene: A Case of Wohlfahrtiimonas chitiniclastica Infection

Summary

A 76-year-old diabetic male with chronic foot ulcers and gangrene, complicated by maggot infestation, was diagnosed with Wohlfahrtiimonas chitiniclastica through metagenomic sequencing. Debridement, ertapenem therapy, and wound reconstruction achieved recovery, underscoring the importance of early detection and advanced diagnostics for rare pathogens in immunocompromised patients.

Abstract

Wohlfahrtiimonas chitiniclastica is a rare Gram-negative bacterium typically associated with wound infections, particularly in immunocompromised patients or individuals exposed to unsanitary conditions. Although clinical cases are infrequent, the infection can lead to severe complications such as bacteremia, septic shock, and even death if unrecognized or inadequately treated. We present the case of a 76-year-old diabetic male who developed chronic, non-healing foot ulcers complicated by gangrene and maggot infestation. Diagnostic challenges were addressed using metagenomic next-generation sequencing, which identified W. chitiniclastica alongside Proteus mirabilis and Corynebacterium striatum. Management included aggressive surgical debridement to remove necrotic tissue, local application of gentamicin-impregnated bone cement, systemic antibiotic therapy with ertapenem, and wound reconstruction using a dorsally based fascial flap. This combined approach resulted in significant clinical improvement, progressive wound healing, and marked reductions in infection markers. The case highlights the decisive role of advanced sequencing technologies in identifying rare pathogens within polymicrobial infections, where conventional methods such as MALDI-TOF mass spectrometry may fail. It also emphasizes the importance of integrating precision diagnostics with surgical intervention, targeted antimicrobial therapy, and rigorous postoperative care to achieve successful outcomes. By documenting this unusual presentation, we aim to expand clinical awareness of W. chitiniclastica infections and provide a practical framework for managing similarly complex diabetic foot infections.

Introduction

Wohlfahrtiimonas chitiniclastica is a Gram-negative, non-motile rod capable of colonizing various hosts under both aerobic and anaerobic conditions, with significant chitinase activity that plays an important role in the metamorphosis of parasitic flies^1,2. Female flies deposit eggs on mucosal surfaces and wounds, creating an infection nidus. The larvae feed on liquid bodily fluids, ingested food, or live and necrotic host tissues for a period of time³. Although infections are rare, the number of clinical reports is increasing, particularly in immunocompromised patients or those with exposure to unsanitary conditions. This trend is partly due to the broader use of genetic sequencing technologies, which has improved understanding of the pathogen's epidemiology⁴. Clinically, W. chitiniclastica can cause localized wound infections but may also progress to severe bacteremia, septic shock, and even death if left untreated⁵.

This case report describes a patient with a chronic, non-healing diabetic foot ulcer complicated by maggot infestation, ultimately diagnosed with W. chitiniclastica infection. The report illustrates the diagnostic challenges and the importance of early identification using metagenomic next-generation sequencing (mNGS). Furthermore, it emphasizes the integration of aggressive surgical debridement with carbapenem therapy to achieve limb salvage. By highlighting the synergy between advanced diagnostics and innovative reconstructive surgery, this case broadens the scenarios in which W. chitiniclastica should be suspected and provides a practical framework for managing similarly complex infections.

CASE PRESENTATION:

A 76-year-old man presented with ulcerations on his right foot that had persisted for three months and progressively led to blackening of the third and fifth toes. Approximately three months before admission, he developed a small ulcer on the plantar aspect of the right forefoot. Over subsequent weeks, the lesion gradually enlarged and produced purulent discharge. He initially sought care at a local hospital, where he received a 5 day course of empirical oral antibiotics (cefuroxime sodium, 1 tablet twice daily) but showed minimal improvement. Fifteen days before admission, the ulcer worsened, with progressive necrosis and maggot infestation.

The patient had a history of diabetes mellitus with poor glycemic control, reporting frequent missed doses and irregular blood glucose monitoring. His regular medications included oral metformin sustained-release tablets (one tablet, three times daily). He also had a history of pacemaker implantation. Socially, he lived in a rural environment with limited access to healthcare and suboptimal living conditions, which may have contributed to delayed wound management. He was a retired manual laborer with a history of chronic tobacco use (approximately 20 pack-years) and occasional alcohol consumption. Family history was negative for diabetes mellitus, peripheral vascular disease, or chronic infectious diseases.

Computed tomography angiography (CTA) of the lower extremities revealed arteriosclerosis in both legs. On admission, laboratory studies demonstrated leukocytosis (WBC 14.74 × 10⁹/L) with neutrophilia (82.1%), elevated C-reactive protein (126 mg/L), and an increased erythrocyte sedimentation rate (72 mm/h), consistent with systemic infection. Glycosylated hemoglobin (HbA1c) was 9.2%. Physical examination revealed marked swelling of the right foot, blackening of the third and fifth toes, diminished dorsalis pedis and posterior tibial artery pulses compared with the contralateral side, loss of superficial sensation in the right lower limb, and absence of pain sensation.

Intraoperatively, gangrene was observed in the third to fifth toes, as well as in the dorsum and sole of the right foot, accompanied by purulent drainage and a foul odor. Active maggots were noted wriggling within the wound (Figure 1 and Figure 2). Necrotic phalanges, tendons, and bone were debrided, and osteomyelitic foci were removed. A dorsally based fascial flap was rotated to cover the exposed plantar bone defect. Irrigation and hemostasis were achieved. Antibiotic-impregnated bone cement, prepared by mixing 0.5 g of gentamicin per 40 g of cement, was applied to the residual bone ends after drilling.

Postoperatively, the patient was treated with intravenous ertapenem (1 g once daily) for 14 days, based on the pathogen profile and clinical response. Intraoperative smear revealed a small number of epithelial cells, numerous Gram-negative bacilli, and Gram-positive cocci and bacilli. Conventional culture identified Staphylococcus faecalis (Group D). Drug susceptibility testing showed sensitivity to vancomycin, penicillin G, levofloxacin, chloramphenicol, ciprofloxacin, and high-level gentamicin in combination, but resistance to high-level streptomycin, erythromycin, and tetracycline. Testing was performed using an automated microbial identification and drug susceptibility analysis system following CLSI M100-33 guidelines. Metagenomic sequencing of intraoperative specimens identified Proteus mirabilis, Wohlfahrtiimonas chitiniclastica, and Corynebacterium striatum (Figure 3). Following surgery and treatment, infection markers decreased significantly, and the wound demonstrated progressive healing.

Diagnosis, Assessment, and Plan:

The patient, a 76-year-old diabetic male with poorly controlled glycemia, presented with chronic right foot ulcers that progressed to gangrene and maggot infestation. Initial evaluation included physical examination, which revealed necrotic toes, purulent drainage, and maggot activity, along with laboratory findings of leukocytosis (WBC 14.74 × 10⁹/L) and neutrophilia (82.1%), consistent with systemic infection. Computed tomography angiography (CTA) of the lower extremities confirmed arteriosclerosis, contributing to impaired perfusion. Intraoperative exploration demonstrated osteomyelitis and extensive necrotic tissue, prompting surgical debridement and microbiological sampling.

Wohlfahrtiimonas chitiniclastica is often isolated in the context of polymicrobial infections. In this case, metagenomic next-generation sequencing (mNGS) identified W. chitiniclastica, Proteus mirabilis, and Corynebacterium striatum. mNGS was chosen because it provides resolution in complex infections that are often undetectable by conventional methods such as MALDI-TOF MS. Differential diagnoses included common diabetic foot pathogens such as Pseudomonas and Staphylococcus species; however, maggot-associated exposure and sequencing confirmed the presence of the rare pathogen.

The treatment plan prioritized surgical debridement to reduce microbial burden, followed by intravenous ertapenem (1 g daily) for broad-spectrum Gram-negative coverage, including W. chitiniclastica, which is typically sensitive to carbapenems. Therapy was planned for 14 days, tailored to the pathogen profile and clinical response. The patient was counseled regarding common adverse effects of ertapenem, including gastrointestinal upset (nausea, diarrhea) and infusion-related reactions, and monitored closely throughout hospitalization. Criteria for adjusting therapy included worsening clinical signs (increasing wound erythema, swelling, or purulent drainage) or elevated infection markers, specifically WBC >15 × 10⁹/L or C-reactive protein >150 mg/L. In such cases, repeat imaging with vascular ultrasound or MRI would be considered, along with antibiotic modification or escalation.

Post-treatment follow-up was structured to ensure continuity of care: wound inspections every 3-5 days during the inpatient period, a comprehensive wound and vascular assessment at 2 weeks post discharge, and monthly reviews for 3 months to monitor wound healing, vascular status, and glycemic control. Wound reconstruction with a dorsally based fascial flap was performed to address tissue loss and promote healing. The choice of ertapenem was supported by its stability against extended-spectrum beta-lactamases and activity against anaerobes, which was critical in the necrotic wound environment. Potential complications included antimicrobial resistance, surgical site infection, or flap failure, necessitating vigilant monitoring. This approach highlights the necessity of advanced diagnostics and multidisciplinary management in immunocompromised patients with rare and complex infections.

Protocol

Written informed consent was obtained from the patient for the publication of clinical details and clinical images, per institutional guidelines. Patient identifiers were anonymized in all documentation.

1. Patient evaluation and initial assessment

1. A comprehensive medical history was obtained, focusing on diabetes mellitus duration, glycemic control (HbA1c levels), history of peripheral vascular disease, and prior interventions (e.g., pacemaker implantation). Chronic foot ulcer progression and maggot infestation were documented.
2. Physical examination assessed right foot swelling, necrotic tissue (third and fifth toes), sensory deficits, and visual confirmation of maggot activity. Wound morphology was photographed (Figure 1 and Figure 2).
3. Laboratory tests included complete blood count (CBC), C-reactive protein (CRP), and erythrocyte sedimentation rate (ESR).
   1. For the CBC, (WBC, neutrophils), whole blood (3 mL) was collected into an EDTA tube, which was inverted gently 8-10x and analyzed within 4 h.
   2. For CRP testing, blood (2-3 mL) was collected in a serum separator tube, allowed to clot for 20-30 min, centrifuged at 1,500-2,000 × g for 10 min, and analyzed the same day.
   3. For ESR, whole blood (2 mL) was collected in a 3.2% sodium citrate tube, mixed gently, and analyzed using the Westergren method within 4 h.
      NOTE: Store/transport blood at 2-8 °C if delayed >1 h.
4. Computed tomography angiography (CTA) of the lower extremities was performed on a slice scanner using the following parameters: helical acquisition from diaphragm to toes, collimation 0.6-0.625 mm, rotation time 0.33-0.5 s, pitch 0.8-1.2, tube voltage 100-120 kVp, current 150-300 mA.
   1. Iohexol contrast (350 mg I/mL, 1.0-1.5 mL/kg, total 80-120 mL) was injected via an 18-20 G antecubital IV at 4-5 mL/s, followed by a 30-40 mL saline flush. Bolus tracking was triggered at 150 HU.
   2. Images were reconstructed at 0.75-1.25 mm slice thickness; Postprocessing of the CT angiography dataset included multiplanar reconstruction (MPR), maximum intensity projection (MIP), and three-dimensional volume rendering (VR).
      1. MPR was performed to reformat the helical acquisition into axial, sagittal, coronal, and oblique planes with 0.75-1.25 mm slice thickness, enabling evaluation of anatomical structures from multiple orientations.
      2. MIP images were generated using slab projections (10-20 mm) to display voxels with the highest attenuation values along each line of sight, thereby enhancing vascular and calcified structures while suppressing surrounding soft tissue.
      3. For VR, the volumetric data were processed on a dedicated workstation with threshold-based segmentation and opacity assignment, producing color-coded 3D models of bone, soft tissue, and vessels that could be rotated and magnified to improve spatial understanding and surgical planning.
5. Handling maggot-infested tissue:
   NOTE: Procedures followed biosafety level 2 (BSL-2). Personnel wore gowns, gloves, eye protection, and N95 masks.
   1. Maggots were removed with forceps under irrigation, placed in sealed containers, and immersed in 70-95% ethanol for disposal.
   2. Contaminated instruments were disinfected with 0.1% sodium hypochlorite for ≥10 min (0.5% for heavy contamination). Infectious waste was bagged in red biohazard bags and autoclaved at 121 °C for ≥15 min or incinerated. Sharps were discarded in puncture-resistant containers.

2. Diagnostic procedures

1. Intraoperative necrotic tissue and purulent drainage were collected as specimens during surgical debridement.
2. Samples were stained by Gram staining and cultured under both aerobic and anaerobic conditions.
3. Metagenomic next-generation sequencing (mNGS) was performed on intraoperative tissue samples.
   1. Tissue biopsies (~0.5 × 0.5 × 0.5 mm) were homogenized in 100 µL of 1× PBS for 5-8 min and adjusted to 200 µL.
   2. DNA and RNA were extracted separately from the homogenized specimens.
      1. For DNA processing, host DNA was depleted by treatment with 1 U Benzonase and 0.5% Tween-20 at 37 °C for 5 min, followed by extraction using the referenced DNA Kit. DNA concentration was quantified using a dsDNA HS assay.
      2. All DNA and RNA libraries were checked using the DNA Kit and quantified with a fluorometer before sequencing.
   3. Libraries were checked and sequenced on a sequencing platform (e.g., SE-75, ~2 × 10⁷ reads/sample). Reads < 50 bp, low-quality, or host DNA were removed.
   4. Microbial reads were aligned to an in-house database. Detection thresholds were as follows: SMRN-r ≥10 (if also in negative control), SMRN ≥3 (if absent in negative control), SMRN >1 for intracellular/hard-to-lyse bacteria; viruses required ≥3 non-overlapping genomic regions; turnaround ~16-19 h.
4. Differential diagnoses included common diabetic foot pathogens such as Pseudomonas aeruginosa and Staphylococcus aureus. These organisms were excluded by mNGS and clinical correlation.

3. Surgical intervention

1. Radical debridement was performed to excise necrotic soft tissue, osteomyelitic bone, and infected tendons. Maggots were manually removed from the wound.
2. Wound reconstruction was achieved by rotating a dorsally based fascial flap to cover the exposed plantar bone defect. Hemostasis was achieved, and the wound was irrigated thoroughly with saline.
3. Antibiotic-impregnated bone cement was prepared by incorporating 0.5 g of gentamicin into 40 g of cement and applied to the residual bone ends after drilling.

4. Antibiotic therapy

1. Intravenous ertapenem (1 g once daily) was administered empirically for Gram-negative coverage, including Wohlfahrtiimonas chitiniclastica, which is typically sensitive to carbapenems.
2. Antibiotic therapy was continued for 14 days and adjusted according to clinical response and infection markers such as WBC count and CRP levels.

5. Postoperative care

1. Blood glucose levels were monitored regularly, and insulin doses were adjusted to maintain HbA1c below 7.5%.
2. The wound was inspected daily for signs of infection, and CBC and inflammatory markers were monitored weekly.

Results

The 76-year-old diabetic male with chronic right foot gangrene and maggot infestation (Figure 1 and Figure 2) underwent comprehensive management, including radical debridement of necrotic tissue, removal of osteomyelitic foci, and wound reconstruction using a dorsally based fascial flap. Metagenomic next-generation sequencing (mNGS) of intraoperative specimens identified Wohlfahrtiimonas chitiniclastica as the primary pathogen, with 97.96% genome covera...

Discussion

Wohlfahrtiimonas chitiniclastica is a rod-shaped, Gram-negative, nonfermenting bacterium that is oxidase- and catalase-positive. It was first discovered in the larvae of the parasitic fly Wohlfahrtia magnifica⁶. Female flies lay eggs on wounds and mucosal surfaces, generating an infection nidus. The larvae feed for a period of time on necrotic or viable host tissues, bodily fluids, or ingested food³. Several factors, including low socioeconomic status, adv...

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Agilent 2100 HS DNA Kit	Agilent Technologies, Santa Clara, CA, USA	5067-4626 (DNA 1000) / 5067-4627 (DNA HS)*	Used for library quality control and fragment analysis
Agilent 2100 HS DNA, Qubit 3.0	Agilent Technologies, Santa Clara, CA, USA	G2939BA	Instrument for library QC, paired with HS DNA Kit
bioMérieux VITEK 2 system	bioMérieux, Marcy-l'Étoile, France	414532	Automated microbial identification and antimicrobial susceptibility testing
Illumina NextSeq 500	Illumina Inc., San Diego, CA, USAIllumina Inc.,	SY-415-1001	High-throughput sequencing platform
QIAamp UCP Pathogen DNA Kit	High-throughput sequencing platform	50214	Pathogen DNA extraction with host DNA depletion
Qubit 3.0 fluorometer	Thermo Fisher Scientific, Waltham, MA, USA	Q33216	DNA and RNA quantification
Siemens SOMATOM Definition AS 64-slice	Siemens Healthineers, Erlangen, Germany	N/A	Used for computed tomography angiography (CTA) imaging