Comparison of a biphasic medium plus routine early subculture with a slide blood culture system.

The accuracy of a biphasic medium plus routine early subculture on chocolate agar was compared with that of a slide blood culture system for detecting facultatively anaerobic bacteria in blood cultures. Over a three month period 2,745 pairs of blood cultures were examined. Bacteremia was diagnosed in 91 patients. Twelve cases would have been missed by using the slide blood culture system alone, in contrast to only three by the biphasic medium alone. The two techniques detected the same amount of contaminant bacteria. Although the slide blood culture system required less time in general, the biphasic medium proved more accurate for isolating Staphylococcus aureus (p = 0.005) and detected gram-positive bacteria more rapidly (p = 0.002).