Pulmonary Nocardiosis Caused by Nocardia otitidiscaviarum and Successfully Treated with Ciprofloxacin Based on Bacterial Identification and Antimicrobial Susceptibility Testing

We report a case of pulmonary nocardiosis caused by Nocardia otitidiscaviarum in a man diagnosed with idiopathic thrombocytopenia who was on oral prednisolone therapy. A chest PET/CT examination 13 days after the start of prednisolone therapy revealed a nodular shadow, and it progressively worsened and was accompanied by cavity formation over time. N. otitidiscaviarum was identified in bronchoalveolar lavage fluid by matrix assisted laser desorption ionization time of flight mass spectrometry. The isolate was eventually confirmed to be N. otitidiscaviarum by a 16S rRNA analysis. There was no evidence of disseminated disease. Combination therapy consisting of oral sulfamethoxazole-trimethoprim (SMX-TMP) and intravenous amikacin and imipenem was initiated, but the SMX-TMP was discontinued because of adverse effects. Antimicrobial susceptibility testing revealed that the isolate was non-susceptible to ceftriaxone, imipenem, minocycline, and clarithromycin. The patient declined long-term intravenous therapy. Oral ciprofloxacin was administered instead, and the pulmonary nocardiosis improved after 6 months of therapy. Bacterial identification and antimicrobial susceptibility testing influence the choice of treatment regimens for nocardia infections by N. otitidiscaviarum, which may be resistant to multiple antimicrobial agents.