The first reported pulmonary nocardiosis caused by Nocardia gipuzkoensis resisted to TMP-SMZ in an immunocompetent patient.

BACKGROUND: . Nocardia gipuzkoensis was first described as a novel and distinct species in 2020 by Imen Nouioui and pulmonary nocardiosis associated with Nocardia gipuzkoensis was once reported in two bronchiectasis patients. Noteworthy, both reported Nocardia gipuzkoensis cases showed sensitivity to Trimethoprim/Sulfamethoxazol (TMP-SMZ), which are usually recommended for empirical therapy.

METHODS: We reported the third case of Nocardia gipuzkoensis infection in a 16-year-old girl with chief complaints of cough, persistent chest and back pain. No underlying immuno-suppressive conditions and glucocorticoid use was revealed. Patchy lesions next to spine and located in the posterior basal segment of lower lobes of left lung were seen in thorax computed tomography (CT), but no pathogenic bacteria was detected according to routine laboratory testings.

RESULTS: Metagenomic next-generation sequencing (mNGS) combined with Whole Genome Sequencing (WGS) was used to classified our isolate from bronchoalveolar lavage fluid (BALF) as a Nocardia gipuzkoensis. It is worth mentioning that drug susceptibility testing of our isolate showed resistance to TMP-SMZ, which was never reported before. The patient improved remarkably both clinically and radiographically according to the treatment with Imipenem-cilastatin infusion alone.

CONCLUSION: mNGS and WGS showed excellent performance in identifying Nocardia genus to the species level and improving detection rate of Nocardia gipuzkoensis ignored by traditional culture. Different from previously reported cases, Nocardia gipuzkoensis infection case showed resistance to TMP-SMZ, which is an unprecedented finding and a crucial addition to our understanding of the antibacterial spectrum of Nocardia gipuzkoensis. The successful treatment with Imipenem-cilastatin infusion alone in this case is a testament to the importance of precise identification and tailored antibiotic therapy.