Monday, June 18, 2018
Saturday, October 22, 2016
Microbiology Questions
1.
Describe
the toxins produced by Cl. Welchii.
2.
Represent
the mechanism of development of Cl. Tetani
infection
3.
Which
microorganisms are responsible for enteric fever? Diagrammatically represent
the course of disease development. Mention its clinical features and complication?
4.
Define
sterilization. Describe the physical modes of
sterilization.
5.
Represent
the path of disease development of C. diptheriae infection. Mention its
clinical features.
6.
Explain
a. Shick’s test
b. Complement fixation test
c. Coomb’s test
Widal test.
Thursday, October 20, 2016
Complement Fixation Test
Complement Fixation Test
The complement fixation test (CFT) is used to detect the presence of specific antibodies in
the patient’s serum. This test is based on the use of complement, a
Biologically labile serum factor that causes the immune cytolysis i.e. lysis of
antibody coated cells.
Principle of complement fixation test
It is the nature of the complement
to be activated when there is formation of antigen-antibody complex.
·
The first step is to heat the serum at 56°C to destroy patient’s
complement.
· A measured amount of complement and antigen are then added to the
serum. If there is presence of antibody in the serum, the complement is fixed
due to the formation of Ag-Ab complex.
·
If no antibody is present then the complement remains free.
· To determine whether the complement has been fixed, sheep RBCs and
antibodies against sheep RBCs are added.
In the positive test : The available complement is fixed by Ag-Ab complex and no
hemolysis of sheep RBCs occurs. So the test is positive for presence of
antibodies.
In the negative test : No Ag-Ab reaction occurs and the complement is free. This free
complement binds to the complex of sheep RBC and it’s antibody to cause
hemolysis, causing the development of pink color.
Procedure
The following figure shows the steps involved in the procedure of complement fixation test.
Interpretation
Positive test : The available complement is fixed by Ag-Ab complex and no
hemolysis of sheep RBCs occurs. So the test is positive for presence of
antibodies.
Negative test : No Ag-Ab reaction occurs and the complement is free. This free
complement binds to the complex of sheep RBC and it’s antibody to cause
hemolysis, causing the development of pink color.
Wednesday, October 19, 2016
Coombs test
A Coombs test (also
known as Coombs' test, antiglobulin test or AGT)
is either of two clinical blood tests used in immuno-hematology
and immunology. The two Coombs tests are the direct Coombs test (DCT, also known as direct antiglobulin test or DAT),
and the indirect Coombs test (also known as indirect
antiglobulin test or IAT)
- The direct
Coombs test is used to detect these
antibodies or complement proteins that are bound to the surface of red
blood cells; a blood sample is taken and the RBCs are washed (removing the
patient's own plasma) and then incubated with anti-human globulin (also
known as "Coombs reagent"). If this produces agglutination of RBCs, the direct Coombs test is positive, a visual indication
that antibodies (and/or complement proteins) are bound to the surface of red blood cells.
- The indirect
Coombs test is used in
prenatal testing of pregnant women and in testing blood prior to a blood transfusion. It detects antibodies against RBCs that are present
unbound in the patient's serum.
Mechanism
The two Coombs tests are based on the fact that anti-human antibodies,
which are produced by immunizing non-human species with human serum,
will bind to human antibodies, commonly IgG or IgM.
Animal anti-human antibodies will also bind to human antibodies that may be
fixed onto antigens on the surface of red blood
cells (also referred to as RBCs), and in the appropriate test
tube conditions this can lead to agglutination of RBCs.
The phenomenon of agglutination of RBCs is
important here, because the resulting clumping of RBCs can be visualised; when
clumping is seen the test is positive and when clumping is not seen the test is
negative.
Common clinical uses of the Coombs test include the preparation of blood
for transfusion in cross-matching,
atypical antibodies in the blood plasma of pregnant women
as part of antenatal care, and detection of antibodies for the diagnosis
of immune-mediated haemolytic
anemias.
The direct Coombs test (also known as the direct antiglobulin test or DAT) is used to detect if
antibodies or complement system factors have bound to RBCs surface
antigens in vivo. The DAT is not currently required for
pre-transfusion testing but may be included by some laboratories.
Examples of
diseases that give a positive direct Coombs test
The direct Coombs test is used clinically when immune-mediated hemolytic anemia (antibody-mediated destruction of
RBCs) is suspected. A positive Coombs test indicates that an immune mechanism
is attacking the patient's own RBCs. This mechanism could be autoimmunity, alloimmunity or
a drug-induced immune-mediated mechanism.
Indirect
Coombs test
The indirect Coombs test (also known as the indirect antiglobulin test or IAT) is used to detect in-vitro antibody-antigen reactions. It is used to detect
very low concentrations of antibodies present in a patient's plasma/serum prior
to a blood transfusion. In antenatal care, the IAT is used to screen pregnant
women for antibodies that may cause hemolytic disease of the newborn.
The IAT can also be used for compatibility testing, antibody identification,
RBC pheno-typing, and titration studies.
Examples of
clinical uses of the indirect Coombs test
Blood
transfusion preparation
Main articles: blood transfusion and cross-matching
The indirect Coombs test is used to screen for antibodies in the
preparation of blood for blood transfusion. The donor's and recipient's
blood must be ABO and Rh D compatible. Donor blood for
transfusion is also screened for infections in separate processes.
·
Antibody screening
A blood sample from the recipient and a blood sample from every unit of donor blood
are screened for antibodies with the indirect Coombs test. Each sample is
incubated against a wide range of RBCs that together exhibit a full range of
surface antigens (i.e. blood types).
·
Cross matching
The indirect Coombs test is used to test a sample of the recipient's
serum for antibodies against a sample of the blood donor's RBCs.
This is sometimes called cross-matching blood.
Courtesy - Wikipedia.
Monday, October 17, 2016
Differnece between Endotoxin and Exotoxin
Differences Between
Exotoxins and Endotoxins
Toxins and enzymes play important role in pathogenecity.
Toxins are of two types:
Endotoxins are heat stable
lipopolysaccharide-protein complexes which form structural components of cell
wall of Gram Negative Bacteria and liberated only on cell lysis or death of
bacteria.
Some of the differences
between
Exotoxins and Endotoxins are as follows:
Exotoxins and Endotoxins are as follows:
S.N.
|
Exotoxins
|
Endotoxins
|
1
|
Excreted by organisms, living cell
|
|
2
|
Found in both Gram positive and Gram Negative bacteria
|
Found mostly in Gram Negative Bacteria
|
3
|
It is polypeptide
|
It is lipopolysaccharide complex.
|
4
|
Relatively unstable, heat labile (60°C)
|
Relatively stable, heat tolerant
|
5
|
Highly antigenic
|
Weakly immunogenic
|
6
|
Toxoids can be madeby treating with formalin
|
Toxoids cannot be made
|
7
|
Highly toxic, fatal in µg quantities
|
Moderately toxic
|
8
|
Usually binds to specific receptors
|
Specific receptors not found
|
9
|
Not pyrogenic usually, Toxin Specific
|
Fever by induction of interleukin 1 (IL-1) production,
Shock
|
10
|
Located on extrachromosomal genes (e.g. plasmids)
|
Located on chromosomal genes
|
11
|
Filterable
|
Not so
|
12
|
It has no enzymatic activity
|
It has mostly enzymatic activity
|
13
|
Its molecular weight is 10KDa
|
Its molecular weight is 50-1000KDa
|
14
|
On boiling it get denatured.
|
|
15
|
Detected by many tests (neutralization, precipitation,
etc)
|
Detected by Limulus lysate assay
|
16
|
Examples: Toxins produced byStaphylococcus aureus,
Bacillus cereus, Streptococcus pyogenes, Bacillus anthrcis(Alpha-toxin,
also known as alpha-hemolysin (Hla))
|
Examples: Toxins produced by E.coli, Salmonella
Typhi, Shigella, Vibrio cholera(Cholera toxin- also known as choleragen)
|
17
|
Diseases: Tetanus, diphtheria, botulism
|
Diseases: Meningococcemia, sepsis by gram negative rods
|
Subscribe to:
Posts (Atom)