Block 1, Unit 9, SK320 Infectious Disease and Public Health

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A set taken from the materials of the Open University's SK320 Infectious Disease and Public Health module, 2012 presentation.

Aerosols

Small drops of airborne liquid or particles that can be breathed in. Aerosols are easily generated by opening lids of bottles containing liquid, including microbial cultures.

Antibody titre

The amount of a specific antibody found in a patient's blood. A high antibody titre reveals that the patient has recently been exposed to the stimulating antigen, and indicates infection by a pathogen.

Antiserum

The amount of a specific antibody found in a patient's blood. A high antibody titre reveals that the patient has recently been exposed to the stimulating antigen, and indicates infection by a pathogen.

Aseptic technique

A technique, or set of techniques, used for the containment and maintenance of microbial cultures in a pure state. Aseptic technique protects the culture, the operator and the environment

Autoclave

A machine that exposes materials to steam at high temperature and pressure, thereby sterilising them. A typical autoclave run exposes material to steam at 121 °C for 15 minutes.

Colony forming unit (cfu)

An individual microbe, or occasionally a group of microbes, that grows on agar to produce a colony.

Complex medium

Growth medium with a chemical composition that is not precisely known. Complex media contain variable components such as yeast extract or partially hydrolysed protein extracts. They are richer than defined media, and are consequently able to support the growth of a wider range of microbes.

Controls

Tests whose results are known, and which are run in parallel with unknown samples. Controls act as internal standards for tests and experiments.

Defined medium

A culture medium that is made of chemically defined nutrients and whose exact composition is known.

Direct immunofluorescence

The use in diagnosis of a fluorescent antibody which binds specifically to an antigen, whose location is thus revealed by the glow of the fluorochrome under appropriate (e.g. UV) illumination.

Enzyme-linked immunosorbent assay (ELISA)

Diagnostic technique in which serum samples containing antibodies are placed in microtitre wells that are precoated with specific microbial antigens. If the patient has antibodies against that antigen, specific binding occurs, and unbound material is then washed out of the wells. Next, an anti-human antibody is added, and this binds to any of the patient's antibodies that remain in the well. Again, unbound material is washed out. The second antibody is attached to an enzyme that catalyses a colour change when its substrate is added. Thus colour changes in the microtitre wells indicate that the patient's serum contained specific antibody and the intensity of the colour reaction can be used for relative quantification.

Enrichment medium

Liquid medium designed to favour the growth of one organism over another.

False negative

Samples that give a negative result in a diagnostic test even though the patients are infected with the disease agent.

False positive

Positive results in a diagnostic test where no infection exists.

Fluorescent antibody technique

Use of antibodies to which are attached fluorochrome molecules that enable specific antigens to be detected visually in samples, under appropriate illumination. The technique is also known as immunofluorescence.

Fluorochrome

A dye that fluoresces (emits visible light) when exposed to light of a shorter wavelength (typically UV, violet or blue light).

Haemagglutination-inhibition assay (HAI)

Diagnostic test used to type influenza virus. The patient's sample is pre-incubated with influenza virus of known haemagglutinin type. If the patient has antibodies to this type, they will bind to the haemagglutinins on the virus particles, and prevent haemagglutination by the virus of added red blood cells. HAI tests are suitable for any viruses or bacteria that are able to agglutinate red blood cells.

Haemagglutination test

Used to detect pathogens that carry haemagglutinin on their surfaces. Patients' samples, possibly containing pathogens, are added to red blood cells. If the samples contain haemagglutinins, e.g. from flu virus, the blood cells will clump and remain in suspension; if not, the blood cells will form a pellet at the bottom of the container.

Hybridoma

A hybrid cell formed by fusion of an antibody-producing B lymphocyte and an immortal myeloma cell. A hybridoma has the immortality of the myeloma cell and the antibody-producing capacity of the normal B lymphocyte.

Indicators

Reagents that, by a colour change or another characteristic property, demonstrate whether a specific substance is present or absent, or give a measure of the substance's concentration, or quantify the extent to which a chemical reaction has occurred.

Indirect immunofluorescence

An immunofluorescent diagnostic technique in which the fluorochrome is not attached to the primary antibody that recognises the target antigen, but to a secondary antibody that binds the primary antibody.

Inoculation

The deliberate introduction of living material into a sterile medium.

Isolation

The separation of a specific microbe from material containing a mixture of microbes.

Lawn

A bacterial culture plated out in such a way that it grows all over the agar plate without any gaps, giving confluent growth.

Microtitre plate

A small plastic tray containing a number of wells, where each well acts like a tiny test tube. These trays allow a large number of reactions to be performed all at once using the minimum of reagents.

Monoclonal antibodies

Monospecific antibodies produced by a culture of hybridoma cells.

Monospecific

Describes antibodies with binding sites for only one epitope.

Negative control

A control in which a vital reagent is omitted, so that the result will be zero - the experiment will definitely not work, and any value obtained from this test system will be the baseline against which all the other results are measured.

Plating out

The placing of bacteria onto a solid growth medium (typically an agar plate) in a Petri dish.

Polymerase chain reaction (PCR)

A technique used to create copies of specific DNA sequences from a DNA template.

Polyspecific

A collection of antibodies that bind several different epitopes.

Positive control

A control that includes a known amount of material that will give a positive result in the test.

Primers

Short stretches of DNA, about 15-20 nucleotides long, that are used to delineate the target sequence in a DNA synthesis reaction such as PCR.

Reference sample

A known amount of a positive control. Knowing the amount of reference sample in the positive control allows the test results to be more quantitative.

Selective medium

A solid medium designed to favour the growth of one organism over another.

Sensitivity

A measure of how much (or how little) of a sample needs to be analysed before a clear-cut result is obtained in a diagnostic test.

Seroconversion

A fourfold increase in specific antibody levels, indicating that the patient has suffered an acute infection.

Serology

The study of antigens and antibodies in patients' sera.

Serum

(Plural, sera.) The part of the blood left behind after cells, platelets and fibrinogen have all been removed, usually by clotting.

Specificity

Relates to the accuracy of the recognition between the test reagent and the patient's sample.

Western blotting

A technique whereby proteins separated out on an electrophoresis gel are transferred to a membrane and proteins of interest within the mixture are identified by probing with specific antibodies. The technique is also known as immunoblotting.

Wet mount

A preparation of a sample on a microscope slide in which the sample is not dried or fixed, but examined immediately under a coverslip.

Zone of inhibition

A circular, clear area around a small paper disc impregnated with antibiotic and placed on a lawn of bacteria where the antibiotic slowly diffuses out into the agar. It indicates that the bacteria could not grow because they were sensitive to the antibiotic used. The size of the zone of inhibition indicates the degree of sensitivity of the bacteria to the antibiotic. If the bacteria are resistant to the antibiotic, they grow right up to the disc.

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