Comparison of Acridine Orange Stain with Culture and Gram Stain of Needle Aspirate in ExperimentalPseudomonasPneumonia

Abstract

The sensitivity and specificity of culture, acridine orange stain, and Gram stain were determined using needle aspiration (NA) material obtained from 82 rats with acute Pseudomonas aeruginosa pneumonia and 18 control rats. Lungs were then processed for either bacterial quantitation or histopathologic examination. NA culture proved to be the most sensitive and specific (55 and 100%, respectively). Sensitivity of acridine orange stain was 40%, whereas Gram stain was only 29%. The specificity of each stain was at least 94%. Lung bacterial concentrations influenced the sensitivities of all three techniques, with better sensitivity found in NA samples obtained from lung with bacterial concentration of at least 10(4) colony-forming units (cfu) of P. aeruginosa. Acridine orange and Gram stain results were similar except in NA samples from lung with bacterial concentration of less than 10(4) cfu in which acridine orange stain was more sensitive. The presence of stains identifying bacteria collected from animals with sterile NA culture was found in a small but significant number of samples, suggesting the presence of nonviable though stainable organisms. Use of all three techniques (culture, acridine orange stain, and Gram stain) increased sensitivity to approximately 70% with minimal decrease of specificity.

Relative Value and Cost-Effectiveness of Culture and Special Stains in Fine Needle Aspirates of the Lung

“…In contrast, the sensitivity of Gram's stain as compared to culture ranges anywhere from 29% to 62%, depending on the clinical setting. 3,4,8 A similar range of sensitivity of Gram's stain is also found in transtracheal aspirates. 8 However, in open lung biopsies, Gram's stain was as sensitive as culture.…”

“…In addition, false positives could be reduced considerably by taking only bacterial cultures from specimens containing acute inflammation or necrosis. Difficulties in the interpretation of Gram's staining have been noted before, with false positive rates between 2% and 16%, 3,4,8,15 and were present with FNA specimens as well. This supports our impression that while interpreting acid-fast smears was the most time-consuming task, interpretation of Gram's stain was the most problematic.…”

“…For example, for most organisms in most pulmonary specimens, cultures appear to be more sensitive than special stains. [2][3][4][7][8][9]14,17,19,21 However, in open lung biopsies, silver and acid-fast stain appear to be more sensitive for fungi and mycobacteria than culture. 15,20 Similar studies comparing the relative sensitivity of culture and special stains in lung FNA specimens have not been performed.…”