Accurate etiological diagnosis of Mycoplasma hominis mediastinitis in immunocompetent patients using metagenomic next-generation sequencing: a case series and literature review

Abstract

Background: As a culture-independent method, metagenomic next-generation sequencing (mNGS) is widely used in microbiological diagnosis with advantages in identifying potential pathogens, guiding antibiotic therapy, and improving clinical prognosis, especially in culture-negative cases. Mycoplasma hominis (M. hominis) mediastinitis is a rare and severe disease for which etiological diagnosis is important but challenging. The application of mNGS in the etiological diagnosis of mediastinitis has seldom been studied.

Methods: By searching the electronic medical history retrieval system with "Mycoplasma hominis" and "mediastinitis", seven patients diagnosed with M. hominis mediastinitis were reviewed in Zhongshan Hospital, Fudan University, Shanghai from 9 December 2020 to 14 February 2023. Microbiological cultures and mNGS were conducted for blood, abscess, and/or mediastinal fluid. Adjustment of the antibiotic therapy due to mNGS was assessed. A literature review was conducted in the PubMed database beginning in 1970 for M. hominis infection and mediastinitis.

Results: For the seven patients, cultures of blood, abscess, and mediastinal fluid were negative whereas mNGS identified M. hominis in serum, abscess, and/or mediastinal fluid and was used to guide specific antibiotic therapy. The stringent mapped reads number of genera (SMRNG), stringent mapped reads number of species (SMRN), and coverage rate of M. hominis detection by mNGS were significantly higher in body fluid (abscess or mediastinal fluid) than in serum. All seven patients had underlying heart diseases and underwent previous cardiac surgery. The most common symptoms were fever and sternal pain. After detection of M. hominis, antibiotics were adjusted to quinolones or doxycycline except for one patient, whose diagnosis was clarified after death. Two patients died. Literature review since 1970 identified 30 cases of extra-genital infection caused by M. hominis. Including our seven new cases, 2 (5.4%) were neonates and 35 (94.6%) were adults. Thirty (81.1%) cases were postoperative infection and 15 (40.5%) had implanted devices. Five patients (13.5%) died.

Conclusions: mNGS might be a promising technology in the detection of fastidious pathogens such as M. hominis. Accurate etiological diagnosis by mNGS could guide antibiotic therapy and facilitate clinical management.

Keywords: Metagenomic next-generation sequencing (mNGS); Mycoplasma hominis (M. hominis); case series; diagnosis; mediastinitis.

Figure 1

¹⁸F-FDG PET/CT showed glucose metabolism increase in paraaortic, pericardial, and mediastinal areas in patient E [(A,B) maximal SUV 28.9] and F [(C,D) maximal SUV 8.4]. R, right; A, anterior; ¹⁸F-FDG, ¹⁸F-fluorodeoxyglucose; PET, positron emission tomography; CT, computed tomography; SUV, standardized uptake value.