Focus
NEW MICROWAVE DIGESTION BOMB
number of enzyme moieties associated with a hybridization site. Other detection strategies being investigated to improve the sensitivity of DNA probe assays include the detection of timeresolved fluorescence from antibodies tagged with lanthanide chelates that exhibit exceptionally long fluorescent lifetimes (Syvanen, Ann-Christine et al. Nucleic Acids Res. 1986,14(2), 1017-28) and a chemiluminescent detection scheme involving the reaction of horseradish peroxidase with luminol, peroxide, and an enhancer (Matthews, Jayne A. et al. Anal. Biochem. 1985,151(1), 205-9). Theoretically, sensitivity can also be improved by increasing the number of target nucleic acid molecules in the original sample. This was recently accomplished when a group from Cetus Corporation developed a DNA probe technique for the diagnosis of sickle cell anemia based on the enzymatic amplification of target DNA sequences by a factor of about a million (Saiki, R. K. et al. Science 1985, 230(4732), 1350-54).
According to Ward, the first DNA probe methodology to be automated involves techniques for the detection of oncogenes or specific pathogens in tissue sections. David J. Brigati of Hershey Medical Center has developed an instrument based on a Fisher Scientific automated slide stainer that will simultaneously process up to 60 in situ hybridizations involving up to 30 different probes. "At the moment," said Ward, "we are seeing the beginning of the automation of DNA sequence analysis. My projection is that in two to five years you'll see DNA probes take their place in the clinical laboratory." This prediction may be of interest to scientific instrument companies such as HP Genenchem, Perkin-Elmer Cetus, Pharmacia, LKB, Applied Biosystems, Varian, and others, which either specialize in biomedical instrumentation or have recently created new divisions and joint ventures to concentrate on equipment for newly developing biotechnological techniques. S.A.B.
Identification of Microorganisms by GC/MS The speed and convenience of microwave heating can now be applied to the digestion of inorganic, organic, or biological materials in a Teflon Lined Bomb. The new Parr 4781 Microwave Digestion Bomb has been designed to combine the advantages of closed high-pressure and high temperature digestion with the requirements of microwave heating. Many samples can be dissolved or digested with less than one minute heating times. As with all Parr Digestion Vessels, careful design and testing effort have gone into the safety and sealing aspects of this unique vessel and operating environment. Call or write for Bulletin 4781 with complete technical details.
PARR INSTRUMENT COMPANY 211 Fifty-third Street Moline, IL 61265 309-762-7716 Telex: 270226
Microorganisms can be differentiated based on chemical analysis of the bacterial cell wall Clinical and biotechnology laboratories have a critical need for rapid and sensitive methods of identifying microorganisms. Classical methods of bacterial identification, however, are often complex and time-consuming, usually involving morphological and metabolic studies as well as tests to determine growth patterns and susceptibility to various antibiotics. In addition, the sensitivity of these traditional identification techniques varies widely depending on the particular microorganism being studied. In an effort to overcome some of these difficulties, Stephen Morgan of the Department of Chemistry and Alvin Fox of the Department of Microbiology and Immunology at the University of South Carolina are working to develop instrumental methods, using capillary gas chromatography/mass spectrometry (GC/MS), for chemotaxonomic characterization of microorganisms. Bacteria can be chemically charac-
CIRCLE 165 ON READER SERVICE CARD 1310 A · ANALYTICAL CHEMISTRY, VOL. 58, NO. 13, NOVEMBER 1986
terized by determination of either metabolic products or structural components, and Morgan and Fox have chosen to concentrate on structural characterization. Structural analysis, they explain, does not require the organisms to be viable, and time-consuming culturing can sometimes be avoided. This may be an important advantage for detection of microorganisms that are difficult or impossible to isolate or that have slow growth patterns, such as those responsible for tuberculosis, leprosy, syphilis, yaws, and Legionnaires' disease. All bacteria are composed of proteins, carbohydrates, lipids, and nucleic acids, but, fortunately, bacterial groups differ in the chemical composition of the structural components of the cell, allowing chemical markers to be used for differentiation. For example, the presence of muramic acid, an amino sugar found only in bacterial cell walls, implies the presence of bac-
