Method for radiorespirometric detection of bacteria in pure culture and in blood

Methods are described for the detection of low numbers of bacteria by monitoring (14)CO(2) evolved from (14)C-labeled substrates. Cell suspensions are filtered with membrane filters, and the filter is then moistened with 0.1 ml of labeled medium in a small, closed apparatus. Evolved (14)CO(2) is collected with Ba(OH)(2)-moistened filter pads and assayed with conventional radioactivity counting equipment. The kinetics of (14)CO(2) evolution are shown for several species of bacteria. Fewer than 100 colony-forming units of most species tested were detected in 2 h or less. Bacteria were inoculated into blood and the mixture was treated to lyse the blood cells. The suspension ws filtered and the filter was placed in a small volume of labeled medium. The evolved (14)CO(2) was trapped and counted. A key development in the methodology was finding that an aqueous solution of Rhyozyme and Triton X-100 produced lysis of blood but was not detrimental to bacteria.