Diagnosis of Mycobacterium marinum Infection by Metagenomic next-generation sequencing.

Background: In December 2023, our hospital confirmed a case of finger infection with Mycobacterium marinum. The patient sought medical attention at our hospital due to a hard scratch on her left middle finger, which was red, swollen, and ulcerated for one month.

Physical examination: A lesion of approximately 1.5 cm x 2 cm in the patient's left middle finger, surrounded by redness and swelling, unclear boundaries, surface rupture, partial scabbing, and no tenderness during compression. She was treated at the previous clinic, common infectious diseases were considered, and was given intravenous infusion treatment: cefotaxime and clarithromycin, and erythromycin ointment was applied externally. She came to our hospital after poor treatment results. The patient has had hypertension for 3 years, no other systemic diseases, no similar medical history among family members, no history of drug or food allergies.

Methods: Clean the wound and remove the scab from the affected area, and use a surgical blade to scrape off necrotic tissue. Send the scraped tissue for pathogen testing: tissue bacterial culture+identification (matrix assisted laser desorption/ionization time-of-flight mass spectrometry, MALDI-TOF), tissue acid fast staining, and tissue metagenomic next-generation sequencing (mNGS). Other auxiliary examinations: blood routine, urine routine, blood fat, liver function, and kidney function.

Results: Tissue bacterial culture+identification: growth of Mycobacterium marinum; Acid fast staining of tissue: positive; Tissue mNGS: Mycobacterium marinum. Clinical treatment plan: clarithromycin 0.5 g bid po+rifampicin 0.45 g qd po+5-aminolevulinic acid photodynamic therapy (ALA-PDT) qw+boric acid wash wet compress tid. After 14 days of treatment, the area of redness and swelling significantly decreased, and the degree of redness and swelling was significantly reduced compared to admission. The degree of ulcer edge protrusion was also reduced compared to admission. There was a small amount of exudation from the wound, and no necrotic tissue was observed. The patient improved and was discharged.

Conclusions: This article reports a case of finger infection with Mycobacterium marinum. Mycobacterium marinum was quickly and accurately identified by mNGS, and reasonable treatment measures were adopted clinically. The patient improved and was discharged. This study has important reference significance for the clinical diagnosis and treatment of Mycobacterium infection. In addition, mNGS as a novel detection method has considerable prospects for rapid diagnosis of pathogens.