A2 Option Module 7

A2 Option Module 7
MICROBES AND DISEASE

Introduction This option module provides for a study in depth of some of the

ways in which microorganisms are used in the rapidly expanding field of biotechnology, and how pathogenic microbes cause disease. The principles involved in culturing microorganisms and obtaining useful products from them provide opportunities for practical experience of basic microbiological techniques. It is essential that all Health and Safety procedures are followed. As well as covering the transmission and effects of bacterial and viral pathogens, the module includes a study of how both natural defence systems and medical treatments can be used to combat disease.

In the assessment of this module a knowledge and understanding of relevant content from Modules 1 to 5 will be assumed.

15.7 Bacteria

Structure and function Characteristic features of bacteria, (including cell wall, cell

membrane, nuclear zone, 70S ribosomes, mesosomes, flagella, plasmids and capsule � as listed in Section 10.2) and the major functions of these structures.

Nutrition and binary fission Bacteria may obtain energy from sunlight, inorganic

substances or from organic substances. (Details of processes not required.)

Binary fission as the main method of reproduction.

15.8 Culturing bacteria

Aseptic techniques Aseptic techniques and health and safety procedures in

handling, culturing and disposing of bacteria.

Monitoring the growth of The techniques of haemocytometry, turbidimetry and bacteria dilution plating.

The distinction between total and viable counts.

Population growth pattern Typical growth curve of a bacterial population and

reasons for lag phase, exponential phase, stationary phase and death phase.

Effect of temperature, pH, nutrient availability and oxygen availability on growth.

Use of a bacterial lawn as a bioassay technique to determine the effectiveness of antibiotics and disinfectants on inhibition of bacterial growth.

Candidates should be able to analyse and interpret experimental data from microbial growth investigations.

15.9 Commercial biotechnology

Screening procedures The advantages of using microorganisms for industrial

processes.

Screening procedures are carried out to identify the most suitable microorganisms to use for a particular process; for example, fungi can be screened for antibiotic production and casein can be used to identify protease production by bacteria.

Continuous and batch The relative advantages and disadvantages of continuous cultures and batch culturing techniques.

Useful products from The microorganisms used and the main stages in the microorganisms production of penicillin.

Downstream processing is carried out to extract and purify the end-product of fermentation.

Candidates should be able to use information provided to explain the purpose of various parts of industrial fermenters and the stages involved in biotechnological processes.

Isolated enzymes It is more efficient to use isolated enzymes than whole

cells because enzyme concentration is higher and there are no unwanted enzymes present.

Immobilised enzymes Isolated enzymes can be immobilised so that they do not

contaminate the end-products and can be used over and over again.

Immobilisation can be achieved by bonding the enzyme with a cross-linking agent, entrapment inside a gel, and by binding the enzyme on to the surface of an absorbing agent.

15.10 Bacterial disease

Pathogenicity The factors affecting pathogenicity of bacteria, to include:

features of cell wall and capsule that affect attachment and entry to host cells;

exotoxins and endotoxins produced by bacteria;

infectivity, exemplified by numbers required to cause Salmonella food poisoning and typhoid fever;

invasiveness, the ability of bacteria to spread within the host.

Transmission Food-borne and water-borne infection, exemplified by

Salmonella food poisoning and E.coli.

Precautions to avoid contamination of food and water.

Human carriers. Treatment of diarrhoea.

15.11 Viral disease

Characteristics of viruses The structural features of a virus, exemplified by the

influenza virus and HIV.

Transmission The course of infection, signs, symptoms and

transmission of influenza and of acquired immune deficiency syndrome (AIDS).

The process of replication of the influenza virus and of the human immunodeficiency virus (HIV).

How viruses cause disease Damage to host cells due to viral replication and the

production of toxins. How HIV causes AIDS. Reasons for the difficulty in treating viral infections.

Candidates should be able to suggest strategies for reducing the incidence of influenza and preventing the spread of HIV.

15.12 Protection against disease

Natural defence mechanisms The roles of the skin, tears, mucus, saliva and cilia in

preventing microorganisms gaining access to living cells.

The process of phagocytosis and the roles of phagocytic white blood cells (neutrophils and macrophages) in destroying, and preventing the spread of, microorganisms that enter the blood and other tissues.

The immune response Antigens, as substances that are �foreign� to the individual organism exposed to them. They usually take the form of a protein, polysaccharide or glycoprotein structure:

on the cell surface of a microorganism;

on the surface of a virus;

on the cell surface of a tissue or organ transplant;

as a free molecule, such as a toxin.

Cell-mediated immunity Production of T lymphocytes in bone marrow and

activation by the thymus. Recognition of antigens by specific, membrane-bound receptor molecules on T lymphocytes. Cloning of T lymphocytes, and destruction of bacteria and cells with antigens.

Antibody-mediated immunity Production of B lymphocytes, and activation by

antigens attached to macrophage membrane. Cloning of B-lymphocytes, and production of specific antibodies. Antibody structure, and formation of antibody-antigen complex.

The role of antibodies in:

agglutination of antigens,

stimulation of phagocytosis,

precipitation of soluble toxins,

preventing pathogenic bacteria attaching to cell membranes.

Immunological memory The production of memory T cells and B cells. The primary and secondary responses. The role of immunological memory in producing a quicker and stronger immune response to a subsequent infection by the same antigen.

The effects of antigenic variability in some pathogens, such as influenza virus, on immunity.

Vaccination The principle that vaccines contain antigens derived from

pathogens, which can protect against infection by that organism.

The principles involved in the production of, and the method of administering, the following types of vaccine:

killed virulent organisms, exemplified by whooping cough;

live non-virulent strains, exemplified by rubella;

modified toxins, exemplified by diphtheria;

isolated antigens from a pathogen, exemplified by influenza;

genetically engineered antigens, exemplified by hepatitis B.

Passive immunity The use of antibodies to counteract possible infection,

and the reason for its temporary effectiveness. Natural passive immunity in young babies.

Antibiotics The mode of action of antibiotics in the treatment of

diseases caused by bacteria and fungi. Effects of antibiotics on cell walls and membranes, and on nucleic acid and protein synthesis.

The principle of selection of particular antibiotics for treatment of specific diseases, and the roles of broad spectrum and narrow spectrum antibiotics.

Antibiotic resistance The process by which an antibiotic resistant strain of

bacterium may develop. Transfer of resistance genes between bacteria. Mechanisms of resistance, such as the production of penicillinase.

The impact of resistant strains on the treatment of disease and the use of antibiotics.