MICROBIOLOGY

ISOLATION OF MICROORGANISMS FROM SPECIMENS: FUNGI: Fungal infections (i.e., mold and yeast infections) often are diagnosed by direct microscopic (fluorescence) examination of specimens. For example, the identification of molds often can be made if a portion of the specimen is mixed with a drop of 10% Calcofluor White stain on a glass slide. Fungal cultures remain as the standard for the recovery of fungi from patient specimens; however, the time needed to culture fungi varies anywhere from a few days to several weeks depending on the organism. Fungal serology (e.g., complement fixation and immunodiffusion) is designed to detect serum antibody but is limited to a few fungi (Blastomyces dermatitidis, Coccidioides immitis, Histoplasma capsulatum). The cryptococcal latex antigen test is routinely used for the direct detection of Cryptococcus neoformans in serum and cerebrospinal fluid. In the clinical laboratory, nonautomated (conventional kits) and aut...

COLLECTION:                       Overall, the results obtained in the clinical laboratory are only as good as the quality of the specimen collected for analysis. Specimens may be collected by several methods using aseptic technique. Aseptic technique refers to specific procedures used to prevent unwanted microorganisms from contaminating the clinical specimen. Each method is designed to ensure that only the proper material will be sent to the clinical laboratory. The most common method used to collect specimens from the anterior nares or throat is the sterile swab. A sterile swab is a rayon-, calcium alginate, or dacron-tipped polystyrene applicator. Manufacturers of swabs have their own unique container design and instructions for proper use. For example, many commercially manufactured swabs contain a transport medium designed to preserve a variety of microorganisms and to prevent multiplication of rapidly gro...

CLINICAL MICROBIOLOGY:                                        Clinical Biochemistry offers an extensive array of biochemical and immunological tests which affords the clinician a wealth of diagnostic information. However, this may lead to confusion when considering the appropriate-ness of a particular test to a given situation or even what type of specimen is required in each circumstance. To look for specific sample requirements and reference ranges for given investigations use the A-Z pad to the right. Clinical Biochemistry performs some routine investigations on behalf of other Pathology disciplines, notably serological screening assays for Virology, antibiotic TDM (Microbiology) and hematological markers of in-vivo haemolysis/ anaemia and malignancy. If the test you are looking for is not listed please contact the laboratory directly for further information.   ...

Plant Viruses and Viroids:                          Plant viruses resemble animal vi ruses in many respects: plant viruses are morphologically similar to animal viruses, and they have similar types of nucleic acid . In fact, some plant vi ruses ca n multiply inside insect cells. Plant  viruses cause many diseases of economically important crops, including beans (bean mosaic virus), corn and sugarcane (wound tumor virus), and potatoes (potato yellow dwarf virus). Viruses can cause color change, deformed growth, wilting, and stunted growth in their plant hosts. Some hosts, however, remain symptom less and only  serve as reservoirs of infection . Plant cells are generally protected from disease by an impermeable cell wall. Viruses must enter through wounds or be assisted by other plant parasites, including nematodes, fungi, and, most often, insects that suck the plant's sap. Once one plant is infected...

PRIONS:               A few infectious diseases are caused by prions. In 1982, American neurobiologist Stanley Prusiner proposed that infectious proteins caused a neurological disease in sheep called scrapie. The infectivity of scrapie-infected brain tissue is reduced by treatment with proteases  but not by treatment with radiation, suggesting that the infectious agent is pure protein. Prusiner coined the name prion for proteinaceous infectious particle.               Nine animal diseases now fall into this category, including the "mad cow disease" that emerged in cattle in Great Britain in 1987. All nine are neurological diseases called spongiform encephalopathies because large vacuoles develop in the brain  The human diseases are kuru, Creu tzfeldt- Jakob disease (ClD), Gerstmann-St riiussler- Scheinker syndrome, and fatal familial insomnia.  These diseases run in f...

Latent Viral Infections : A virus can remain in equilibrium with the host and not actually produce disease for a long period, often many years. The oncogenic viruses just discussed are examples of such latent infections. All of the human herpesviruses can remain in host cells throughout the life of an individual. When herpesviruses are reactivated by immunosuppression (for example, AIDS), the resulting infection may be fatal. The classic example of such a latent infection in viruses is the infection of the skin by herpes simplex virus, which produces cold sores. This virus inhabits the host's nerve  cells but causes no damage until it is activated by a stimulus such as fever or sunburn- hence the term fever blister. In some individuals, viruses are produced, but symptoms never appear. Even though a large percentage of the human population carries the herpes simplex virus, only iO to 15% of people carrying the virus exhibit the disease. The virus of so...

DNA Oncogenic Viruses :                          Oncogenic viruses are found within several families of DNA containing viruses. These groups include the Adenoviridae, Herpesviridae, Poxviridae, Papovaviridae, and Hepadnaviridae. Among the papovaviruses, papillomaviruses cause uterine (cervical) cancer. Virtually all cervical cancers are caused by human papillo ma  virus  (HPV); HPV- 16 accounts for about half of all cervical cancers. A vaccine against four HPVs, including HPV- 16, is recommended for 11 - to 12 -year-old girls. Epstein-Barr (EB) virus was isolated from Burkitt's lymphoma cells in 1964 by Michael Epstein and Yvonne Barr. The proof that EB virus can cause cancer was accidentally demonstrated in 1985 when a 12-year-old boy known only as David received a bone marrow transplant. Several months after the transplant, he died of cancer. An autopsy revealed that the virus had been unwi...

MULTIPLICATION OF ANIMAL VIRUSES:  The multiplication of animal viruses follows the basic pattern of bacteriophage multiplication but has several differences.  Animal viruses differ from phages in their mechanism of entering the host cell. Also, once the virus is inside, the synthesis and assembly of the new viral components are somewhat different, partly because of the differences between prokaryotic cells and eukaryotic cells. Animal viruses may have certain types of enzymes not found in phages. Finally, the mechanisms of maturation and release, and the effects on the host cell, differ in animal viruses and phages. In the following discussion of the multiplication of animal viruses, we will consider the processes that are shared by both DNA- and RNA-containing animal viruses. These processes are attachment, entry, uncoating, and release. We will also examine how DNA- and RNA-containing viruses differ with respect to  their process of  biosynthesis...

VIRUS IDENTIFICATION:    Identifying viral isolates is not an easy task. For one thing, viruses cannot be seen at all without the use of an electron microscope. Serological methods, such as Western blotting, are the most commonly used means of identification. In these tests, the virus is detected and identified by its reaction with antibodies.  Virologists can identify and characterize viruses by using such modern molecular methods as use of restriction fragment length polymorphisms (RFLPs) and the polymerase chain reaction(PCR).PCR PCR was used to amplify viral RNA to identify the west Nile virus in 1999 in the United States & SARS-associated coronavirus in china in 2002. Viral Multiplication:  The nucleic acid in a virion contains only a few of the genes needed for the synthesis of new viruses. These include genes for the virion structural components, such as the capsid proteins, and genes for a few of the enzymes...