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Search for better health Part 3 Louis Pasteur Robert Koch During the second half of the nineteenth century, the work of Pasteur and Koch and other scientists stimulated the search for microbes as causes of disease 1 describe the contribution of Pasteur and Koch to our understanding of infectious diseases Louis Pasteur (1822-1895) Created the science of microbiology Demonstrated that microbes caused the souring of wine and beer (lactobacilli) Development of the process of pasteurisation to kill bacteria Conducted the swan-necked flask experiment to disprove spontaneous generation Established the germ theory of disease, that microbes caused disease Robert Koch (1843-1910) Developed many bacteriological techniques Developed the agar plate technique for growing microorganisms Identified the bacterium Bacillus anthracis responsible for anthrax disease. Demonstrated that specific microbes are responsible for causing specific diseases Developed Koch’s postulates Identified the bacterium responsible for tuberculosis and cholera Developed a vaccine for chicken cholera Used Koch’s work on anthrax to develop a vaccine for anthrax Developed a vaccine against rabies and used it on humans for the first time Established the principle of immunity and developed an effective way to prevent infectious disease Pasteur’s Flasks Pasteur’s early research suggested the existence of spores. He hypothesised that these spores were carried in air, where they were inactive. They developed into active microorganisms when nutrients became available. Pasteur designed the experiment as shown below. The flasks with the S shaped neck allowed air to enter but dust and spores were trapped in the neck and could not reach the broth. The other flask was directly open to the air. Pasteur boiled the broth and subjected the glassware to steam to kill any microbes present. As Pasteur predicted the glassware with the S bend did not become contaminated proving that the organisms that contaminated the broth must be carried in the air. Pasteur’s flasks are still on display in the Pasteur Institute in Paris and after 150 years they are still not contaminated. 2 Koch’s Postulates Koch developed a set of procedures to follow, which will definitely and scientifically identify the pathogen. These procedures are known as “Koch’s Postulates” and are still used today when previously unknown infectious diseases are discovered. Koch was the first person to develop a set of rules (postulates) which linked a particular organism with a particular disease. He was the first to develop a way of growing pure cultures of bacteria on agar in a Petri dish. He stained, described and identified many bacteria including TB, cholera and anthrax. The organism believed to be the cause of the disease must always be present when the disease occurs. The organism must be isolated from the host and grown in pure culture. Organisms from the pure culture, when inoculated into healthy, suitable, susceptible hosts must produce the disease. The organism must be re-isolated, grown in pure culture and compared to the organism first injected. 3 distinguish between: prions viruses bacteria protozoans fungi macro-parasites and name one example of a disease caused by each type of pathogen Pathogen Prion Virus Bacteria Characteristics Defective proteins: proteinaceous infectious particle Minuscule Not cellular No nucleic acids Causes degeneration of brain tissue Diseases can be both hereditary and infectious Tiny: 30 to 300 nm Not cellular Can only reproduce using host cells Can be crystallised Small: 0.5 to 5 µm Cellular Procaryotic: no membrane bound organelles Single strand of DNA Reproduce by binary fission quickly inside a host Waste products (toxins) often harm host Classified by shape 4 Example Fatal Familial Insomnia Influenza Tuberculosis Protozoa Fungi Macro-parasites Small: 2 to 1000 µm Eucaryotic: membrane-bound nucleus No cell wall Many are free-living Classified by the way they move Range in size, unicellular to multicellular Eucaryotic: membrane-bound nucleus Cell wall No chloroplasts Saprophytic (living on dead matter) or parasitic Visible by the naked eye Endoparasites or exoparasites Endoparasites usually have long association with host Ectoparasites usually have brief association with host Prion 5 Amoebic dysentery Thrush Tapeworm, lice Virus Bacteria 6 Protozoa identify the role of antibiotics in the management of infectious disease When is a Microbe a Pathogen? There are many microorganisms around us. Some cause us no problems, some are beneficial and some cause disease. An organism is a pathogen if it causes disease. Antibiotics are chemical substances which destroy bacteria or inhibit their growth. They target the bacteria without destroying the host. They are not effective against viruses (other types of antimicrobial drugs can kill viruses and fungi). Mode of action: some antibiotics kill the microbe by destroying the cell wall eg Penicillin (discovered by Alexander Fleming in 1928) Some inhibit protein synthesis, bacteria are unable to make essential compounds, resulting in the death of the cell)eg tetracyclines and streptomycin. Others destroy the cell membrane thus effectively destroy the bacteria eg amphotericin Broad spectrum antibiotics act against a wide range of bacteria. 7 perform an investigation to model Pasteur’s experiment to identify the role of microbes in decay gather and process information to trace the historical development of our understanding of the cause and prevention of malaria identify data sources, gather process and analyse information from secondary sources to describe one named infectious disease in terms of its: – cause – transmission – host response – major symptoms – treatment – prevention – control process information from secondary sources to discuss problems relating to antibiotic resistance 8