Postoperative intra-abdominal infections caused by Metamycoplasma hominis: diagnostic clues from an eight-case series

OBJECTIVES: Postoperative Metamycoplasma hominis infections are likely underrecognized because routine microbiological methods frequently fail to detect the organism. We characterized the clinical and microbiological features of postoperative M. hominis infections identified after optimization of diagnostic methods. METHODS: We retrospectively reviewed adult patients (≥18 years) with postoperative intra-abdominal M. hominis infections identified between January 2015 and November 2025 at a Japanese tertiary-care hospital. RESULTS: Eight women (median age, 39 years) with postoperative M. hominis infections were identified; seven had undergone obstetric or gynecologic surgery. Following recognition of the initial case in 2020, increased clinical suspicion, communication with the microbiology laboratory, and optimized culture conditions (blood/chocolate agar in 5% CO₂, Brucella HK agar under anaerobic conditions, and prolonged incubation) helped identify seven additional cases through 2025. All patients developed deep pelvic infections with persistent inflammatory findings despite empirical β-lactam therapy. Gram stains of purulent specimens showed abundant leukocytes without visible organisms. All patients achieved clinical cure following targeted antimicrobial therapy. CONCLUSION: M. hominis should be considered in β-lactam-refractory postoperative intra-abdominal infections with negative Gram stains. Active clinical suspicion and optimized microbiological methods facilitate its diagnosis.