Week 9

Once again, this weeks notes are largely copied from Dr Matewele's notes.
Lecture Topic:
Medical microbiology
○ Microbial flora may produce products such as bacteriocins that inhibit other organisms, and so protect us from pathogens
○ Microbial flora also stimulate the immune system, e.g. antibodies against "friendly" E coli also protect against pathogens such as E coli O157:H7.
○ Stem cells can be described a pluripotent haemopoietic (blood making) cells that can form different type of blood cells, eg white blood cells and red blood cells. T cells develop in a primary lymphoid organ called the thymus, and B cells develop and mature in another called the bone marrow. Immune responses take place in secondary lymphoid organs, e.g. lymph nodes for responses in tissues, and the spleen for responses in blood.
○ Animals reared in sterile environments do not develop the lymphoid system properly, as it is not challenged.
○ Colonisation: where microorganisms multiply in the body - if these are non pathogenic, they become part of the microbial flora. If they are pathogenic they cause an infection - this does not necessarily mean a disease. A disease develops when the body functions are affected.
○ Sources of pathogens:
§ Human to human - eg S aureus
§ Animal to human - eg rabies, influenza - also known as zoonotic infections. - note: influenza has about 8 chromosomes, which recombine - eg from dogs & poultry
§ Soil to humans - e.g. Clostridium tetani
§ Water to human - eg Vibrio cholerae causes cholera, Legionella pneumophila causes Legionnaires Disease.
§ Air to humans - e.g. Mycobacterium tuberculosis
§ Insect vectors - Malaria - transmitted by anopheles mosquitoes - Plasmodium.
○ Epidemiology - practiced by epidemiologists, who study and monitor the incidence and control of diseases. Incidence is classified as:
§ Outbreak - where it is sudden, within a segment of a population.
§ Epidemic - unexpected occurrence of a disease in a large population. May be common source, sudden but limited in extent (e.g. cholera from a contaminated pump) or propagated, gradual growth (e.g. Common cold or Spanish flu).
§ Pandemic - world wide.
§ Endemic - constantly at low level in community.
○ The pathogenicity of the microorganism is associated with virulence factors, such as capsules, which resist phagocytosis, toxins, e.g. in Corynebacterium diptheriae, often produced by bacteriophages that infect bacteria.
○ The microorganisms initially interact with the host either by attaching to epithelial cells ( e.g. in the genitourinary tract for Neisseria gonorroea, or digestive tract for Salmonella spp.)
○ Invasive microorganisms may produce enzymes e.g. protease to break down protein, the popular term "flesh eating bacteria" for Streptococcus pyogenes. In addition it produces streptokinase, a fibrinolysin, to dissolve clots.
○ Staphylococcus aureus produces coagulase, which produces coagulation. The fibrils in the coagulant can then be used for protecting the microorganism. It also produces a protein that binds to the fc (fraction crystallisable) region of antibodies, preventing an immune response.
○ Clostridium perfringens produces lecithinase, which breaks down lecithin in cell membranes, causing cytolysis, and hyaluronidase, which breaks down hyaluronic acid, the cement binding cells together.
○ Thus, some organisms, such as Strep pyogenes, Staph Aureus, and C perfringens are invasive.
○ Others, such as C perfringens produce a theta toxin, which causes diarrhoea, and S aureus produces toxic shock syndrome.
○ Beneficial effects:
§ Vaccines
§ Antibiotics
§ Human proteins (e.g. insulin)
§ Transformation of steroids
§ Food Production (Brewing, Cheese, etc)
§ Probiotics can incorporate "Friendly bacteria" into animal feeds, e.g. Lactobacillus to reduce or control Salmonella,
§ DNA vaccines, where the dna has a code for the parasite proteins
§ Bacteriophages to control pathogens such as E coli O157
§ Prevention of ulcers by vaccination against Helicobacter pylori
§ An understanding of how prions cause disease can help to identify molecules that inhibit prion mechanism.