We report the case of an 88-year-old woman who was admitted with pneumonia. Sputum examination revealed aerobic actinomycetales, and we initiated the patient on therapy with imipenem/cilastatin (IPM/CS). However, the fever persisted, and the radiological findings started to worsen. On day 6 of the illness, N. otitidiscaviarum was identified by MALDI-TOF MS (Matrix As- sisted Laser Desorption Ionization Time of Flight Mass Spectrometry). We changed the antibacterial drug to ST, following which the patient improved. It has been reported that some bacterial species causing pulmonary nocardiosis show natural resistance to certain antibiotics. While not downplaying the significance of culture and drug sensitivity examinations, we suggest that for rare bacterial species, such as in the present case, the application of MALDI-TOF MS for identifying the bacterial species potentially allows early selection of effective therapeutic agents.
