The genus Nocardia, ubiquitous in the environment of water and soil, is a slow-growing and partially acid-fast positive, aerobic actinomycete [15]. Nocardiosis might range from pneumonia to cutaneous diseases in immunocompromised patients and occasionally in individuals with normal immunity [11,20]. Some studies suggested that the incidence of nocardiosis is continually increasing due to the rise in the number and survival of immunocompromised patients, and improved methodology for detecting Nocardia [1,11,21,27,28].

The similarity in clinical manifestation of nocardiosis and tuberculosis underscores the importance of accurate pathogen identification. However, to date, the clinical diagnosis of nocardiosis remains difficult due to its slow growth and lack of effective measures [11].

In most clinical laboratories, the routine microbiological methods for Nocardia involve direct smear microscopy for Gram staining and/or modified acid-fast staining and blood agar plate (BAP) culture, but neither is sensitive [16]. Occasionally, Nocardia was isolated from the BACTEC MGIT 960 culture system (MGIT 960), an automated system for culturing Mycobacterium tuberculosis (MTB) and non-tuberculosis mycobacteria (NTM) [19]. The MGIT 960 system can incubate and continuously monitor 7-ml culture tubes, and a mixture of antibiotics, including polymyxin B, amphotericin B, nalidixic acid, trimethoprim, and azlocillin (PANTA) is added to the broth to increase the positive rate of this system [17,18].

Currently, only limited evaluation data are available on the above Nocardia detection methods, especially MGIT 960 [12,19]. Thus, we initiated a study to evaluate the performance of MGIT 960 in different clinical samples for detecting Nocardia. At the same time, the recovery yields of the combination the various methods, namely, BAP, smear microscopy and MGIT, were also analyzed in this retrospective study.