Definitions

Question 1

What is a superantigen?

Answer 1

Superantigens are a class of antigens that cause non-specific activation of a large mass of T-cells resulting in polyclonal T cell activation and MASSIVE cytokine release -> e.g. Toxic shock syndrome toxin (s.aureus)

this toxins bind simultaneously to TCR and MHC without requiring an antigen

The large number of activated T-cells generates a massive immune response which is not specific to any particular epitope on the SAg thus undermining one of the fundamental strengths of the adaptive immune system, that is, its ability to target antigens with high specificity. More importantly, the large number of activated T-cells secrete large amounts of cytokines, the most important of which is Interferon gamma. This excess amount of IFN-gamma in turn activates the macrophages. The activated macrophages, in turn, over-produce proinflammatory cytokines such as IL-1, IL-6 and TNF-alpha. TNF-alpha is particularly important as a part of the body’s inflammatory response. In normal circumstances it is released locally in low levels and helps the immune system defeat pathogens. However, when it is systemically released in the blood and in high levels (due to mass T-cell activation resulting from the SAg binding), it can cause severe and life-threatening symptoms, including shock and multiple organ failure.

Question 2

What is an exotoxin?

Answer 2

An exotoxin is a toxin secreted by bacteria. An exotoxin can cause damage to the host by destroying cells or disrupting normal cellular metabolism. They are highly potent and can cause major damage to the host. Exotoxins may be secreted, or, similar to endotoxins, may be released during lysis of the cell.

They may exert their effect locally or produce systemic effects. Well-known exotoxins include: botulinum toxin produced by Clostridium botulinum; Corynebacterium diphtheriae toxin, produced during life-threatening symptoms of diphtheria; tetanospasmin produced by Clostridium tetani. The toxic properties of most exotoxins can be inactivated by heat or chemical treatment to produce a toxoid. These retain their antigenic specificity and can be used to produce antitoxins and, in the case of diphtheria and tetanus toxoids, are used as vaccines.

Question 3

What is the generation time (cultivation time)?

Answer 3

the generation time is the time interval required for a cell (or population) to divide.

Normally around 20 min. Slow growth for mycobacterium tuberculosis. Colonies after 4-6 weeks!

Question 4

Disinfection

Answer 4

Disinfection = decrease of germ count (pathogens)

reduce the amount of patogens, inactivate them, and thus prevent infections

Question 5

Sterilisation

Answer 5

Sterilisation = inactivation of all forms of microbial life (pathogenic and pathogenic microbes, spores!)

Question 6

What are the difference between asepsis and antisepsis?

Answer 6

Asepsis: protect human body (and materials) from infective agents
Antisepsis: destroy the disease causing infective agents

Question 7

Define bacteriostatic and bactericidal effect

Answer 7

A bacteriostatic agent, is a biological or chemical agent that stops bacteria from reproducing, while not necessarily killing them otherwise

-MIC = minimal inhibitory concentration [μg/ml, mg/l]

Bactericidal is an agent that destroys bacteria

• MBC = minimal bactericidial concentration [μg/ml, mg/l] - The lowest concentration of an antibiotic that kills 99,9 % of a certain quantity of bacteria

Question 8

Define Chemotherapeutic Index

Answer 8

The ratio of the minimal effective dose of a chemotherapeutic agent to the maximal tolerated dose. Originally used by Ehrlich to express the relative toxicity of a chemotherapeutic agent to a parasite and to its host.

Maximal tolerated dose / minimal effective concentration

Ki = DTM/DCM,

DTM: dosis tolerata maxima (highest dose that is tolerated by the host)
DCM: dosis curativa minima (lowest dose that terminates infection)

Question 9

What are agglutination and what can cause it?

Answer 9

The clumping of cells such as bacteria or red blood cells in the presence of an antibody or complement. The antibody or other molecule binds multiple particles and joins them, creating a large complex. This increases the efficacy of microbial elimination by phagocytosis as large clumps of bacteria can be eliminated in one pass, versus the elimination of single microbial antigens. Another example occurs when people are given blood transfusions of the wrong blood group.

O-antigen - Gram- wall antigen
H-antigen - Pili antigen
K-antigen - Capsular antigen

Question 10

What is precipitation and what can cause it?

Answer 10

Precipitation reactions are based on the interaction of antibodies and antigens. They are based on two soluble reactants that come together to make one insoluble product, the precipitate

Macromolecular such as toxins and enzymes can precipitate.

Question 11

What is a titre in lab testing?

Answer 11

titre: the smallest amount of antibody, which can cause positive reaction

Question 12

What are virulence?

Answer 12

Virulence - the objective, quantitative measurement of the pathogenicity of a certain microorganism.

Pathogenicity: It’s the ability of a certain microorganism (species) to cause disease in a certain host (human, animal).

Question 13

Transport medium

Answer 13

A medium for transporting clinical specimens to the laboratory for examination, and able to keep the organism for 48 hours

Question 14

Pathogenicity

Answer 14

the condition or quality of being pathogenic, or the ability of the microbe to cause disease in the host

Question 15

Agglutination

Answer 15

Antigen- antibody reaction ends up in visible sedimentation of Ag-Ab complex. The antigens are cellular or the Ag is bound to a particle of cellular size. It is used for detecting antigens from specimens with known antibody or to detect antibodies with known antigens. E.g.: serotyping of E.coli isolates.

Question 16

What is ELISA?

Answer 16

Enzyme-linked immunosorbent assay (ELISA) :a test that uses antibodies and color change to identify a substance.

Question 17

What is immunofluorescence?

Answer 17

Immunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on microbiological samples.

Use antibodies with a fluorescent dye to detect a specific antigene.
Direct and indirect methods

Question 18

Transport culture media

Answer 18

Transport media. Allow growth of bacteria

Question 19

Catalase positive

Answer 19

Have the catalase enzyme

Catalase-reaction: 2H2O2 2H2O + O2

Positive: Staphylococcus genus
Negative: Streptococcus genus

Question 20

Coagulase positive

Answer 20

Have coagulase, a protein enzyme produced by several microorganisms that enables the conversion of fibrinogen to fibrin. Coagulase reacts with prothrombin in the blood. The resulting complex is called staphylothrombin, which enables the enzyme protease to convert fibrinogen, a plasma protein produced by the liver, to fibrin. This results in clotting of the blood.

used to distinguish between different types of Staphylococcus isolates. Importantly, S. aureus is generally coagulase-positive, meaning that coagulase negativity usually excludes S. aureus.

Coagulase positive:
Staphylococcus aureus

Coagulase negative:
Staphylococcus epidermidis,
Staphylococcus haemolyticus,
Staphylococcus saprophiticus,
Staphylococcus hominis

Question 21

Spore

Answer 21

In biology, a spore is a unit of asexual reproduction that may be adapted for dispersal and for survival, often for extended periods of time, in unfavorable conditions. By contrast, gametes are units of sexual reproduction. Spores form part of the life cycles of many plants, algae, fungi and protozoa. Bacterial spores are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions.

Question 22

Biofilm

Answer 22

Biofilms are usually found on solid substrates submerged in or exposed to an aqueous solution, although they can form as floating mats on liquid surfaces and also on the surface of leaves, particularly in high humidity climates. Given sufficient resources for growth, a biofilm will quickly grow to be macroscopic (visible to the naked eye). Biofilms can contain many different types of microorganism, e.g. bacteria, archaea, protozoa, fungi and algae; each group performs specialized metabolic functions. However, some organisms will form single-species films under certain conditions. The social structure (cooperation/competition) within a biofilm depends highly on the different species present

Biofilms have been found to be involved in a wide variety of microbial infections in the body, by one estimate 80% of all infections. Infectious processes in which biofilms have been implicated include common problems such as bacterial vaginosis, urinary tract infections, catheter infections, middle-ear infections, formation of dental plaque, gingivitis, coating contact lenses, and less common but more lethal processes such as endocarditis, infections in cystic fibrosis, and infections of permanent indwelling devices such as joint prostheses and heart valves. More recently it has been noted that bacterial biofilms may impair cutaneous wound healing and reduce topical antibacterial efficiency in healing or treating infected skin wounds. Early detection of biofilms in wounds is crucial to successful chronic wound management. Although many techniques have developed to identify planktonic bacteria in viable wounds, few have been able to quickly and accurately identify bacterial biofilms. Future studies are needed to find means of identifying and monitoring biofilm colonization at the bedside to permit timely initiation of treatment