Predictive value of Gram staining of low respiratory tract secretions paired to routine culture.

Microbiological methods such as Gram staining and culture of low respiratory tract secretions are necessary to detect the real bacterial pathogens that cause lower respiratory tract infections (LRTI). In many cases, Gram stain analysis may be unreliable to determine the cause of LRTI, and bacterial cultures provide adequate information. However, we herein report two cases of lower respiratory tract infections, diagnosed with the aid of microscopic examination of Gram staining, while routine cultures were negative in 48 h. Case 1. A 74-year-old woman was referred to the hospital with the chief complaints of cough, fever, expectoration and episodes of hemoptysis lasting one month. A protected specimen brush (PSB) and a brochoalveolar lavage (BAL) were successively obtained. The samples were processed with Gram staining and routine cultures, done within 0.5 h of obtainment. On Gram staining, the organisms appeared as Gram-positive thin branching, beaded, coccoid fi laments. Modifi ed ZiehlNielsen staining (with 1% sulphuric acid) showed many acid-fast thin branching beaded fi lamentous structures, consistent with the morphology of Nocardia species. Meanwhile, the results of culture on blood agar and chocolate agar were negative at 37°C after 48 h. Small, dry, wrinkled, irregular, yellowish white colonies appeared on blood agar and chocolate agar after 72 h of incubation, which was also identifi ed as Nocardia asteroides by standard bacteriological methods.