Micro CH. 15

3 major microbial identification techniques

-Phenotypic

-Immunologic

-Genotypic

Phenotypic

Observation of microbe’s microscopic and macroscopic morphology, physiology, and biochemical properties

Immunologic

Analysis of microbe using antibodies, or of patients’ antibodies using prepackaged antigens

Genotypic

Analysis of microbe’s DNA or RNA

What are the different phenotypic methods used?

-Types of enzymatic activities it can carry out

-Physical conditions it thrives in

-Antibiotics it is susceptible to

-Chemical composition of its walls and/pr membranes

What are drawbacks of phenotypic testing methods that require culturing the pathogen?

They are not automated, are often not as precise compared to other methods

What is serology?

Involves in vitro testing of serum, urine, cerebrospinal fluid, whole tissues, and saliva for the presence of specific antibodies; presence can reveal the history of a patient’s contact with microorganisms or other antigens

What is sensitivity?

detection of even minute quantities of antibodies or antigens in a specimen; reflects the degree to which a test will detect every positive person

What is specificity?

property of a test to focus only on a certain antibody or antigen, and not react with an unrelated or distantly related antigen

What is “lab on chip”?

Many genetic tests have been miniaturized and placed on chips (integrated circuits) that are easy to use, requiring few supplies and little technical training; it’s available for DNA and RNA sequencing as well as PCR methods

Western blot test

-proteins within cell lysates are separated via electrical charge within a gel

-Proteins in the gel are transferred to a special filter

-filter is incubated with antibody solutions labeled with radioactive, fluorescent, or luminescent molecules

-sites of specific antigen-antibody binding will appear as a pattern of bands that can be compared to known positive and negative controls

Direct fluorescent antibodies

-unknown test specimen or antigen is fixed to a slide and exposed to FAb solution

-if antigen-antibody complexes form, they will remain bound to the samples and will be visualized by fluorescence microscopy

-valuable for identifying and locating microbial antigens on cell surfaces or tissues and in identifying the causative agents of syphilis, gonorrhea, and meningitis

Indirect fluorescence antigen test

-FAbs recognize the Fc region of antibodies in patient sera

-known antigen is added to the test serum

-binding of the fluorescent antibody is visualized through fluorescence microscopy

-Fluorescing aggregates or cells indicates the FAbs have complexed with microbe-specific antibodies

-used to diagnose syphilis and various viral infections

Enzyme-linked immunosorbent assay (ELISA)

-uses and enzyme-linked indicator antibody to visualized antigen-antibody reactions

-relies on a solid support such as a microtiter plate that can adsorb the reactants

The property of a test to detect even small amounts of antibodies or antigens that are test targets is

Sensitivity

Horseradish peroxidase and alkaline phosphatase are enzymes used in _________blank tests.

ELISA

In precipitation tests, the antigen

is a soluble molecule

Immunologic methods of identifying microorganisms in a patient sample are characterized as those that

rely on the specificity of antibodies to target a single antigen

Phage typing is useful in identifying _________

Salmonella

Which test is the confirming test for people who initially tested antibody-positive in the screening ELISA test for HIV?

Western blot

The _________blank of a test means the test can detect even very small concentrations of the antigen or antibody being analyzed, whereas the _________blank of a test focuses on the ability of a test to only detect the desired antigen or antibody without reacting with other unrelated substances

sensitivity; specificity

Which of the following is not a phenotypic method of identification?

Antibody response

_________blank is the branch of immunology that traditionally deals with in vitro diagnostic testing of serum, although the field has expanded to include other types of samples such as urine, saliva, and cerebrospinal fluid.

Serology

Syphilis can be diagnosed most easily by ________

direct fluorescence