The rapid laboratory diagnosis of anaerobic infection.

In order to assess the rapid laboratory diagnosis of anaerobic pyogenic infection, we compared the results of Gram stains, ultra-violet fluorescence and gas chromatography, all performed directly on pus, with those of anaerobic culture. Fluorescence was most rapid but there were many negatives unless Bacteroides melaninogenicus was present. Gas chromatography was rapid and sensitive but there were some false negatives, often in pure Bacteroides fragilis infection, and a few false positives. Gram-staining was also rapid, but only helpful on its own when there were large numbers of organisms of mixed or characteristic morphology. The three methods together almost always provided a reliable and rapid presumptive diagnosis of anaerobic pyogenic infection.