Microorganisms, if present in the blood samples, metabolize nutrients in the
BACTEC
culture vial and release CO
2
into the medium or utilize the oxygen
in the medium. The instrument monitors the fluorescence of the vial sensor
which increases as CO
2
is produced or oxygen is utilized. Analysis of the
rate and amount of CO
2
produced or O
2
utilized
enables the instrument to
determine if the vial is positive; i.e., the presumptive presence of viable
organisms