Rapid visual detection of microorganisms in blood culture

We describe a method and apparatus for rapid visual detection of microorganisms in blood cultures. In the 30-min procedure, a lysing reagent for the preferential digestion of blood cells and a concentration device which causes 1 ml of lysed specimen to pass through a portion (3 mm2) of a membrane filter (pore size, 0.6 micron) were used. After the material remaining on the filter was Gram stained, the filter was mounted and examined microscopically. The ability to detect microorganisms in blood cultures was determined by spiking seven common blood pathogens into blood cultures prepared from the blood of healthy volunteers. Microorganism concentration in the cultures ranged from 1 to 1,000/ml. All of 34 cultures with at least 100 CFU/ml were detected, 34 of 64 cultures with less than 100 CFU/ml were detected, and 41 of 42 negative controls were correctly reported as negative.