New targets for DNA probes.

Genes in the cell nucleus are in obvious target for new diagnostic techniques that identify a microorganism by the presence of characteristic DNA segments (SN: 8/18/84, p. 104). But in their search for ways to distinguish similar organisms or to detect a quite divergent set, researchers are now looking beyond the nucleus.

The parasitic disease called leishmaniasis is caused by about a dozen species of protozoa, each triggering characteristic symptoms that range from self-healing skin lesions to fatal infection of internal organs. Determining exactly what species are responsible is important for selecting the appropriate treatment. Scientists at Codon, a biotechnology company in Brisbane, Calif., and at Walter Reed Army Institute of Research in Washington, D.C., report that the have devised DNA segments, or probes, that can distinguish among several species of Leishmania. They used DNA not form the cell nuclei but from an accessory body, called the kinetoplast or micronucleus, which is found in many protozoa. "These experiments," the scientists say, "suggest that DNA probes made from Leishmania kDNa [kinetoplast DNA] may be useful tool for diagnosing leishmaniasis and predicting the severity of the disease."

Another probe directed to nucleic acids outside the cell nucleus is the basis of the first product released by a San Diego company called Gen-Probe. This probe detects mycoplasma in laboratory tissue-culture samples. Mycoplasma contamination is a frequent and troublesome problem in laboratories. David E. Kohne of Gen.-Probe has produced DNA segments that bind specifically to the RNA in ribosomes of two genuses of mycoplasma but not to mammalian RNA. Because there are thousands of ribosomes in a cell, this technique is more sensitive than if it were to detect nuclear DNA, Gen-Probe says. Because, in addition to contaminating tissue cultures, mycoplasma infects the human respiratory tract, Gen-Probe has plans to use their DNA probe in clinical tests for respiratory tract infections.