Recent Microbial Techniques Developed in
Diagnosing Some Common Diseases
Diagnostic microbiology: Recent Advances
Diagnostic medical microbiology is concerned with the
etiologic diagnosis of infection. Diagnostic microbiology
encompasses the characterization of thousands of agents that
cause or are associated with infectious diseases.
The techniques used to characterize infectious agents vary
greatly depending on the clinical syndrome and the type of
agent being considered, be it virus, bacterium, fungus, or
parasite.
Because no single test will permit isolation or
characterization of all potential pathogens, clinical
information is much more important for diagnostic
microbiology than it is for clinical chemistry or
hematology.
Many pathogenic microorganisms grow slowly, and
days or even weeks may elapse before they are isolated
and identified. Treatment cannot be deferred until this
process is complete.
After obtaining the proper specimens and informing the
laboratory of the tentative clinical diagnosis, the clinician
should begin treatment with drugs aimed at the organism
thought to be responsible for the patient's illness. There are
many diagnostic.
Methods used in diagnostic microbiology are often used to
take advantage of a particular difference in organisms attain
information about what species it might be, often through a
reference of previous studies.
Hence, it is necessary to come up with smarter ways of
diagnosing these microbes and their pathogenic mechanisms
with these diagnostic methodsRapid antigen detection
Rapid identification after culture
Conventional tests
ELISA test
Continued
Molecular detection (nucleic acid probes and nucleic acid
amplification)
Rapid biochemical tests
Direct microscopy
Radiology
Serology
Biomarkers
Molecular typing
Laboratories are Evolving
Today, laboratory medicine is developing at a rapid
pace and the microbiology lab is having its own
evolution going on. Lab automation is emerging and
processes are done faster than ever with more
standardized and comparable tests.
Rapid antigen detection test
A rapid antigen detection test is a test that is able to detect
the presence of a pathogen in minutes, compared to the
lengthy time needed to grow a pathogen and identify it in the
lab.
How is this possible? All pathogens have molecules on
them that the immune system can recognize.
These molecules are called antigens and are unique to each
pathogen. A rapid antigen detection test uses antibodies that
attach to a specific antigen to detect its presence.
If the sample contains the pathogen, the antigens
will attach to the labelled antibodies during the rapid
antigen detection test and allow the doctor to identify
the pathogen causing the illness.
Not all pathogens have rapid antigen detection test
available, but many do including the bacteria that
causes strep throat, as well as viral infections such as
dengue fever virus and Zika virus.
Process
There are several techniques used during rapid antigen
detection tests but the most common is the lateral flow
immunoassay.
During this type of test, a sample is applied to a test strip.
On the strip are antibodies coated with a tag, such as gold or
a fluorophore, that will allow for visual detection if the
antigen is present.
The sample containing the antigen is applied on the strip
and attaches to the tagged antibodies. Then, the antibodyantigen mixture passes over the test line, another area
coated in antibodies against the antigen. These antibodies
isolate the sample along the test line if it is positive for the
antigen.
The sample then flows over a control line, which contains
antibodies against the gold coated antibodies. This line does
not detect the antigen, but rather is a control to make sure
the strip is working properly. If there is no color along the
control strip then the test is void.
This type of test usually
takes less than 15 minutes.
If the antigen is present, a
colored line will appear in
the test line region,
indicating a positive result.
Process of a lateral flow immunoassay for rapid
antigen detection tests
Elisa: Enzyme-Linked Immunosorbent Assay
 ELISA detects substances wit antigenic
properties (mainly proteins)
 Based on enzymatic color-reaction
Basic principle of ELISA
Enzyme is used to detect the binding of Antibody - Antigen
Enzyme converts colorless substrate into colored product,
indicating the presence of Antibody - Antigen complex
ELISA can be used to detect either presence of Antigens or
Antibodies
ELISA is one of the most common assays used for detection
of pathogens such as Salmonella, L. monocytogenes. E. coli
0157:H7, and C. Jejuni, or their toxins.
Binding of antigen (pathogens or toxins) to primary
antibody is quantitatively measured in a 96-well
polystyrene plate (microtiter plate) by using a secondary
antibody conjugated to an enzyme.
Enzymes used in ELISA include Alkaline Phosphate,
Peroxidase and ß Galactosidase.
During indirect ELISA the Ag is trapped between two Ab
molecules (sandwich ELISA)
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The amount of enzyme present is estimated by the
calorimetric determination of catalysis of the substrate
and is proportional to the amount of antigen present.
Three forms of ELlSA assays are generally used:
(i) indirect
(ii) sandwich
(iii) competitive inhibition assay