Evaluation of acridine orange stain for detection of microorganisms in blood cultures

A pH 4.0 buffered solution of the fluorochrome acridine orange was used to stain samples of 2,704 blood cultures that failed to yield visible evidence of growth after 1 day of incubation. Results obtained by the staining method were compared with those obtained by aerobic and anaerobic subcultures simultaneously performed upon the same cultures. Of the 109 culture-positive blood specimens initially detected by the acridine orange and the subculture methods, 85 (78%) were detected by both acridine orange and subcultures techniques, 14 (12.8%) were detected by subculture alone, and 10 (9.2%) were detected by acridine orange alone. The differences between the subculture and acridine orange methods were not found to be statistically significant (P less than 0.1). The acridine orange method represents a rapid and inexpensive alternative to conventional subculture techniques for the detection of bacteria in blood cultures that fail to yield visible evidence of growth after 1 day of incubation.