Posts

Showing posts from May, 2013

CLINICAL 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 automated methods for rapid identificatio…

CLINICAL MICROBIOLOGY

Image
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 growing members of the population . However,
with the exception of the nares or throat, the us…

CLINICAL MICROBIOLOGY

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.
                        Clinical microbiology is concerned with the investigation, diagnosis and, in an advisory capacity, management of infection caused by microorg…

VIROLOGY

Image
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,
it can spread infection to other plants in its pollen and seeds.
In laboratories, plant viruses ar…

VIROLOGY

Image
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 families,
which indicates a possible genetic cause. However, they cannot
be purely inherited, because mad cow disease arose from
fe…

VIROLOGY

Image
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 some
latent infections can exist …

VIROLOGY

Image
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 papilloma 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 unwittingly
introduced into the boy with the bone marrow transplant.   
 Another DNA virus that causes cancer is h…

VIROLOGY

Image
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. 









Attachment:  Like bacteriophages, animal viruses …

VIROLOGY

Image
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 used in the viral life cycle.
These enzymes are synthesized and functional on…