Molecular Identification
Charles R. Vossbrinck
Most of us, scientists included, have the illusion that the degree of detail with which we have identified a living thing is appropriate. For some, it is enough to know that they have trees and flowers growing in their front yards; for others, it is important to recognize whether the trees are oaks or elms and the flowers are daffodils or chrysanthemums.
Today's technology allows us to identify any living thing to any level of precision - by using a single cell. This technology uses molecular probes that bind only to the DNA of targeted organisms, is based on gene amplification that multiplies a millionfold the DNA of interest, and involves comparing specific pieces of DNA between organisms.
Molecular identification has two important advantages over conventional techniques of microscopic examination. Identification can be made using a very small amount of material, and is much more accurate than with previous methods - a species, a population, or even an individual can be identified.
Applications. Several applications of this technology are already being used. Individual humans have been identified from a single hair, a drop of blood, or a scraping of skin. Such forensic information has already has been used as conclusive evidence in cases of paternity, homicide, and sexual assault.
Gene amplification has great application in the area of medical diagnostics. Commercial tests are now available to identify, with precision, such disease- causing bacteria as Legionella (Legionnaire's disease), Mycoplasma pneumoniae (pneumonia), and Neisseria gonorrheae (gonorrhea). And in the food industry, bacterial diagnostics, also based on gene amplification, includes tests for Salmonella, Staphylococcus, and Listeria, which all cause food poisoning.
Current research. Research in the Office of Agricultural Entomology at the University of Illinois focuses on both the identification of insects and of the microorganisms associated with insects. Comparison of pieces of DNA has already been used to determine the evolutionary relationships between a group of flies, the Calypterates. This group includes many agricultural and medical pests, such as horn flies (pest of dairy cattle), face flies, tsetse flies (which transmit African sleeping sickness), flesh flies, blow flies, bot flies (parasites of horses and cattle), and house flies.
With a grant from the National Institutes of Health, we are examining opportunistic parasites of humans who have compromised immunological systems. For example, with their impaired immunological defenses, many AIDS patients have become infected with microsporidia, parasites that ordinarily cannot attack humans. We use molecular identification techniques to determine the origin of these microsporidia or which organisms transmit them to humans, and how to prevent their transmission.
Another project uses genetic probes to identify the areas of the southern United States that corn earworms and corn leaf aphids come from and determine if these insect pests are carrying transmissible plant diseases. Unable to survive Illinois winters, they migrate to Illinois from the south each spring. We hope that the information obtained will eventually allow us to make early crop control recommendations.
Other projects under way include the differentiation of populations of corn rootworms and of insect pests of livestock. Future applications of molecular identification are limited only by need, ingenuity, and imagination.
Charles R. Vossbrinck, assistant professor of agricultural entomology