Microbial count in a liquid, such as water, milk, or soft drinks for human consumption and water for microelectronic and pharmaceutical product processing is of the utmost importance to health and product integrity, respectively. Microbial count analysis typically consists of a labor intensive manual membrane filtration followed by a 48 to 72 hour incubation period.
The results of the microbial analysis are interpreted by a trained analyst who visually counts the number of colonies on the filter paper after incubation. Each colony represents a single colony forming unit (CFU) in the initial sample. From this information, the number of CFUs per unit volume is determined.
Bioluminescence has been utilized by both the food industry and medical field to detect high concentrations of microbes. The detection process consists of measuring adenosine triphosphate (ATP); a nucleotide found in all living cells. ATP, the primary energy donor in viable cells, rapidly degrades as the cell dies. With the use of the enzyme luciferase (see U.S. Pat. No. 4,833,075), ATP can be measured.
ATP is released from living bacterial cells with the use of a bacterial release agent which lyses microbial cell walls. In the presence of oxygen (0.sub.2), magnesium (Mg.sup.++) and luciferase, ATP drives the conversion of luciferin to oxyluciferin. This reaction results in the conversion of ATP to adenosine monophosphate (AMP) and the release of a photon of light. ##EQU1## The light can be measured by a luminometer if the concentration of microbes is about 1.times.10.sup.5 CFU per milliliter (ml) or greater, the current sensitivity for the state of the art. Note, bioluminescence is typically utilized for grossly concentrated samples, not for trace level analysis.
This process is typically accomplished by sequentially adding a bacterial release agent, luciferin/luciferase, and Mg.sup.++ to a liquid sample while a fixed luminometer records any offsets due to emitted light from the sample.
What is needed in the art is a microbial monitoring process which is automated, has high sensitivity, is zero gravity compatible, and has a decreased incubation period.