Fundamental Food Microbiology, Third Edition - Fuad Fathir

566 FUNDAMENTAL FOOD MICROBIOLOGY
luciferin–luciferase (from firefly) system in the presence of Mg 2+ , the ATP concentration
in the lysed cells in a sample is measured. The method can detect as low as
10 2–3 viable bacterial cells and ca. 10 yeast cells/g or /ml of a food. It can also be
used to determine microbial population on equipment surfaces. The method is very
rapid, and several automated systems with methods to use them are now commercially
available.
In another method, the genes encoding bacterial bioluminescence (lux gene)
from luminous bacteria (e.g., Vibrio spp.) have been cloned in some pathogenic,
indicator, and spoilage bacteria important in food. Bacterial luciferase catalyzes
oxidation of reduced flavin mononucleotide (FMNH 2) and a long-chain aliphatic
aldehyde by molecular O 2 and emits light. Because only live cells can produce light,
the bacterial strains containing the cloned lux gene can be used to determine the
effectiveness of methods employed to kill cells or remove from food and food
environments very rapidly. It is also used to detect injured bacteria incapable of
producing light, but able to do so following repair of injury. Automated systems to
measure light from the reaction are now commercially available.
Many other rapid methods, automated systems, and miniature versions of traditional
methods are now commercially available. Some have been discussed in more
detail in the references listed and can be consulted.
REFERENCES
1. Vanderzant, C. and Splittstoesser, D.F., Ed., Compendium of Methods for the Microbiological
Examination of Foods, 3rd ed., American Public Health Association, Washington,
D.C., 1992.
2. Richardson, G.H., Ed., Standard Methods for the Examination of Dairy Products,
15th ed., American Public Health Association, Washington, D.C., 1985.
3. Food and Drug Administration, Bacteriological Analytical Manual, 6th ed., Association
of Official Analytical Chemists, Arlington, VA, 1992.
4. Fung, D.Y.C., Rapid Methods and Automation in Food Microbiology, Marcel Dekker,
New York, 1994, p. 357.
5. Vasavada, P.C., and White, C.H., Rapid methods and automation in dairy microbiology,
J. Dairy Sci., 76, 3101, 1993.
6. Stewart, G.S.A.B. and Williams, P., Shedding new light on food microbiology, ASM
News, 59, 241, 1993.