A quantitative assay for the detection of hepatitis B virus DNA employing a biotin-labeled DNA probe and the avidin-beta-galactosidase complex

16 Methods for Detecting Microbial Pathogens in Food and Water

Newly developed methods for the detection of bacteria and viruses have provided microbiologists with the means to rapidly identify and monitor specific microorganisms in food and water. Traditional methods of testing involve culture techniques to increase the numbers of the organism to a detectable level, followed by isolation and biochemical identification. This chapter focuses on the methodologies to detect pathogens and indicator organisms; however, the methods described are applicable to most bacteria. As detection and isolation methods have improved, a growing number of pathogens have been identified as important food- and waterborne pathogens. This chapter describes the use of nucleic acid and antibody probes that have the potential to circumvent the need to culture the organism prior to identification. Nucleic acid probes have become a valuable diagnostic reagent in the identification of human and animal pathogens and have made possible the identification of viruses and bacteria that are difficult, if not impossible, to cultivate. DNA probes have also proved to be a useful tool for identifying and monitoring the organisms in food and the environment.

Immunoenzymatic techniques applied to the specific detection of nucleic acids. A review

Numerous enzymatic and chemical methods are now available for the preparation of non-radioactive nucleic acid probes. Labels, such as enzymes, fluorophores, lumiphores can be attached to the nucleic acid probe either by covalent bonds (direct labelling) or by biospecific recognition after hybridization (indirect labelling). The principle of the latter method is based on the use of a hapten-labelled nucleic acid probe which is generally detected by an immunoenzymatic assay. Indirect labelling has several advantages: this procedure uses multienzyme complexes to increase the number of enzyme molecules associated with hybridization and hence provides an increase in detectability; moreover, haptens (biotin, dinitrophenol, acetylaminofluorene analogues, digoxigenin, brominated or sulphonylated pyrimidines) used to label nucleic acid probes are not sensitive to elevated temperatures (42-80 degrees C), extended incubation times (several hours), detergents and organic solvents currently required in hybridization techniques. The application of the immunoenzymatic and related techniques to nucleic acid probing is reviewed, focussing on the strategies of non-radioactive hybridization, hapten-labelling of nucleic acids and methods for the immunodetection of the hybrids.

Determination of the sex of chickens by a biotin-labeled deoxyribonucleic acid probe

Repeating units of the W chromosome-specific, XhoI-family repetitive DNA of chickens have been cloned and sequenced. The recombinant plasmid carrying the .7 kilobase (kb) W chromosome-specific repeating unit was labeled by biotinylated deoxyuridine 5'-triphosphate and used to determine the sex of White Leghorn chicken by two DNA hybridization techniques. Hybrids formed were detected by the streptavidin-alkaline phosphatase method. By Southern blot hybridization, XhoI-.7 kb, XhoI-1.1 kb, and EcoRI-1.3 kb fragments were detected in the genomic DNA from the female White Leghorn but not in the DNA from the male. By dot-blot hybridization, which is the most convenient way to detect a specific nucleotide sequence, the difference between male and female could be clearly detected not only using purified DNA samples but also using blood cells or even blood itself as samples.