A Rare Catch in a Nonhealing Wound

Introduction. Mycobacterium smegmatis is a common microbe found in soil, dust, and water that rarely causes infections in humans. Case Report. A 45-year-old man with a past medical history of hypertension presented with a nonhealing surgical wound in his anterior chest wall, measuring 0.5 cm x 0.5 cm x 0.3 cm with minimal serosanguinous drainage, that had been present for more than 1 year. Wound swab showed M smegmatis. He required a 3-month course of antibiotic treatment and advanced wound care that included packing the sinus wounds with silver-alginate dressings for the first 2 weeks followed by iodoform packing; once the infection and drainage had improved after 2 months of treatment, packing was changed to a collagen dressing. He responded well to treatment, and the ulcers completely closed at the end of his 3-month course. Conclusions. This case illustrates the importance of considering atypical microbial infections in the workup for chronic nonhealing wounds.

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Mycobacterium smegmatis is a common microbe found in soil, dust, and water that rarely causes infections in humans. Most reported cases of M smegmatis infections are associated with direct inoculation of contaminants into soft tissues.¹ Herein, the authors report a case of M smegmatis infection in a nonhealing chest wound. 

A 45-year-old man with a past medical history of hypertension referred himself to the Wound Care and Hyperbaric Center at Houston Methodist Hospital (Houston, TX) for a nonhealing surgical wound in his anterior chest wall lasting more than 1 year. One year prior to presentation, the patient had been involved in an accident with a half-pound of explosives. He had sustained a shrapnel injury to his chest wall that resulted in an open chest wound.

Based on old medical records received from the initial treating hospital, at the time of his initial injury, the patient was found to have a sucking chest wound measuring 25.4 cm x 38.1 cm that extended inferiorly from his left nipple to over the left costal margin. He underwent emergent surgical removal of the foreign body fragments, and a pectoralis major flap was used for surgical reconstruction of the chest wall. After creation of the surgical flap, he had a left chest wound measuring 10.16 cm x 12.7 cm that required full-thickness skin graft placement. The skin graft was harvested from his right thigh. He also underwent pericardiotomy, chest tube placement for pneumothorax, and open reduction and internal fixation of his fractures as well as surgical excision and debridement of extensive wounds.

During the postoperative period, he developed sepsis and required serial surgical debridements with empiric antibiotic coverage. Imaging at the outside hospital (computed tomography chest with contrast) did not reveal any osteomyelitis. Over the course of the next 3 months, the patient developed several sinus tracts over his wounds. These sinus tracts produced thick, serosanguinous discharge and caused severe pain. Upon discharge, he continued dry dressings as needed whenever he had open wounds. The patient described his wounds as sinus tracts that appeared closed for a few days but then they would reopen on their own, causing him frustration; the reopened wound appeared as pictured in the Figure. Unfortunately, the authors did not have access to images of the patient’s wound at initial presentation to the outside hospital.

Two years after the initial injury, the patient referred himself to the Wound Care and Hyperbaric Center for further wound care management and a second opinion for a wound measuring 0.5 cm x 0.5 cm x 0.3 cm with a small amount of serosanguinous fluid drainage. Wound cultures from swab with acid-fast bacillus (AFB) testing showed the presence of M smegmatis. Given abnormal wound cultures corresponding to the high clinical suspicion, invasive imaging with intravenous (IV) contrast was deferred at this point. As per the recommendation of an infectious disease specialist, a 3-month course of antibiotic treatment (IV amikain 15 mg/kg twice daily, oral isoniazid 300 mg once daily, and oral rifampin 600 mg once daily) was initiated.

During the 3-month course of antibiotic therapy, advanced wound care was also utilized, including packing the sinus wounds with silver-alginate dressings for the first 2 weeks followed by iodoform packing for 8 weeks; the dressing was changed after 2 weeks due to the silver-alginate dressing making the wound bed appear darker and the patient requested a change in the type of dressing. Once the drainage decreased and wound improved after 10 weeks, the iodoform packing was changed to a collagen dressing (PureCol Collagen dressing; Advanced BioMatrix, Inc, San Diego, CA) until the wound closed (last 2 weeks of treatment). Wound drainage completely resolved by the end of his 3-month treatment course.

Due to the extremely small wound size (0.5 cm x  0.5 cm x 0.3 cm), negative pressure wound therapy could not be initiated. He responded well to the above treatment and the ulcer resolved by the end of the 3 months without any complications. The patient was discharged from the clinic with instructions to return in case the wound reopened. Follow-up phone call by clinic staff at 1-month post discharge confirmed wound closure with no issues.

Mycobacterium smegmatis is found in normal human genital secretions as well as in the environment (soil and water).² Although it was first recognized in 1884, it was long thought to be a nonpathogenic microbe; it was first reported as a human pathogen in 1986.² According to Runyen’s classification of nontuberculous mycobacteria,³M smegmatis is a type IV (ie, rapidly growing mycobacteria). Most reported cases of M smegmatis infection in humans involve skin and soft tissues, especially associated with inoculation from foreign bodies.¹ It has been reported to cause disseminated infections in immunocompromised patients.⁴ To the best of the authors’ knowledge, this is the first case of M smegmatis infection resulting from a shrapnel injury to the chest.

In the present case, the temporal relationship of the accident and nonhealing ulcer over an extensive period of time (ie, 1 year) suggests this could be a rare and invasive infection of M smegmatis or other mycobacterium species. This prompted the authors to request AFB on the wound cultures to look for  M avium complex species. The dramatic improvement of the wound when the appropriate antibiotics were administered suggests this microbe was the cause of poor wound healing.

Since this is a rare infection,¹ there is no evidence to guide treatment strategies. However, a review of the literature shows most cases of M smegmatis infections require extensive debridement with prolonged antibiotic treatment followed by skin grafting.^1,2

The patient reported on herein responded well to advanced wound treatments (ie, adequate wound packing with silver-alginate dressings, iodoform, and a collagen dressing) for healing after the infection subsided and appropriate antibiotic coverage for M smegmatis. This patient received a 3-month course of antibiotic treatment, as per indications by an infectious disease consultant.

The results of this case of a nonhealing surgical chest wound illustrate the importance of considering atypical microbial infections in the workup for chronic nonhealing wounds.

Affiliation: Houston Methodist Hospital, Houston, TX

Correspondence: Manjulatha Badam, MD, CWS, Houston Methodist Hospital, 6565 Fannin Stress, Suite 1001, Houston, TX 77004; mlatha.badam@gmail.com

Disclosure: The authors disclose no financial or other conflicts of interest.