Diagnostic challenges in postoperative pelvic infections associated with Metamycoplasma hominis: a two-case analysis using metagenomic sequencing

Postoperative gynecological infections may present diagnostic challenges, particularly in the presence of fastidious genital mollicutes and inherently mixed microbial DNA, both of which limit the diagnostic performance of microbiological methods, including Gram staining, conventional culture, 16S rRNA gene PCR followed by Sanger sequencing. This study aimed to illustrate the limitations of conventional microbiological methods in the diagnosis of gynecologic pelvic infections and highlight key considerations for the clinical use of metagenomic next-generation sequencing (mNGS), based on two contrasting cases of postoperative pelvic infections associated with Metamycoplasma hominis ( M. hominis ). In both cases, neither conventional culture nor 16S rRNA gene PCR/Sanger sequencing identified the causative organism, and shotgun mNGS was subsequently performed. Although the mNGS findings differed markedly between the two cases, M. hominis was considered the most plausible pathogen. These two cases show that the clinical relevance of organisms detected by mNGS should not be judged by read counts alone, particularly in non-sterile specimens or after antibiotic exposure. Even low-abundance reads may represent clinically meaningful pathogens when interpreted within the clinical context. They also highlighted the value of mNGS as a complementary diagnostic tool for gynecological pelvic infections when conventional diagnostic methods are intrinsically limited.