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ANTIGEN. Any substance that induces an immune response in the body, particularly the production of Antibodies They do not necessarily cause disease. Self Antigen.
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ANTIGEN Any substance that induces an immune response in the body, particularly the production of Antibodies They do not necessarily cause disease
Self Antigen • Self antigens are substances (usually proteins or polysaccharides) that are present in self tissue and would not normally provoke an immune response unless in a diseased state.E.g. - Rhesus markers found on blood cells- MHC complex glycoproteins
Non-self antigens Any Foreign substance that causes an immune responsee.g. - Pollen- Bacteria- Viruses- Prions- Protein markers from other animals
Disease A disease is any change that impairs the normal function of an organism.
SIZE MATTERS • Endemic: A disease or a condition that's transmitted at the usual expected rate in a small area. • Epidemic: A disease or condition that spreads rapidly through a segment of a population. • Pandemic: A disease or condition occurring throughout the population of a country, a people or the world.
Disease Non infectious Infectious Also called Non-communicable diseases are those diseases that are not caused by a pathogen and cannot be communicated from one person to another. caused by either the environment, nutritional deficiencies, lifestyle choices, or genetic inheritances. Also called contagious diseases are caused by a pathogen and are transmissible from one person to another.
PathogenA pathogen is a biological agent that causes disease to its host. Non cellular pathogens Cellular pathogens Pathogens that are not made up of cells. Egvirus,prions,viroids Pathogens that are made up of cell. Eg. Bacteria, amoeba, fungi,worms.....
Bacteria • Bacteria are single-celled organisms.
BACTERIA Structure • Bacteria have these features: • cell wall containing a special polymer called peptidoglycan. • Cell membrane • Plasmids containing genetic information • Ribosomes • Bacteria also often have these features: • flagella • movement • pili • attachment • Capsule
BACTERIACapsule / slime layer • Some bacteria are enclosed within a capsule. This protects the bacterium, even within phagocytes, helping to prevent the cell from being killed. Bacteria which lack the capsule are easily killed by the immune system.
Endospores • Some bacteria can form very tough spores, which are metabolically inactive and can survive a long time under very harsh conditions. • Allegedly, some bacterial spores that were embedded in amber or salt deposits for 25 million years have been revived. These experiments are viewed skeptically by many scientists. • Anthrax has survived for millions of years in its endospore form. • Spores can also survive very high or low temperatures and high UV radiation for extended periods. This makes them difficult to kill during sterilization.
BACTERIA Reproduction • They reproduce by binary fission, which is like mitosis. Under favourable conditions, a bacterial cell divides by fission once in every 20 minutes.
BACTERIA MOVEMENT: Chemotaxis • The flagellar motor is reversible: • Counterclockwise rotation: bacterium moves in a straight line • clockwise rotation: bacterium tumbles randomly • the motor periodically reverses, causing a random change in direction: bacteria move in a random walk. • : bacteria move toward the source of nutrients by swimming up the chemical gradient. Or, away from a toxin.
BACTERIA Shape • Spirillumis spiral‐shaped. • Bacillus is an elongated or rod‐shaped bacteria. • Coccusbacteria are spherical. Cocci and bacilli tend to form clusters and chains.
Classification of bacteria • Aerobic and anaerobic bacteria:Bacteria are also classified based on the requirement of oxygen for their survival. • Autotrophic and heterotrophic bacteria: • Gram Positive and Gram Negative bacteria:Bacteria are grouped as ‘Gram Positive’ bacteria and ‘Gram Negative’ bacteria, which is based on the results of Gram Staining Method
Gram positive and negative • The Gram test (invented by Hans Gram) is supposed to test for toxicity by detecting LPS. • Gram positive means nontoxic, • Gram negative means toxic. However there are many exceptions.
How Gram Stains are Made Gram‐positive bacteria stain purple; Gram‐negative bacteria stain pink. This difference is dependent on the thick or thin (respectively) peptidoglycan cell wall.
Gram test Gram Positive Bacteria Gram Negative Bacteria In Gram-positive cells, peptidoglycan makes up as much as 90% of the thick, compact cell wall. Gram-positive bacteria, which have peptidoglycan as the outermost layer, are more susceptible to these antibiotics. The cell walls of Gram-negative bacteria are more chemically complex, thinner and less compact, with peptidoglycan comprising only 5 – 20% of the cell wall. The outer membrane of Gram negative bacteria is similar to the plasma membrane, but less permeable and composed of lipopolysaccharides (LPS), a harmful substance classified as an endotoxin. Because of the outer LPS layer of Gram-negative cells, antibiotics can’t easily get to the peptidoglycan.
Most of us are helpful........ • Only 1% of bacteria are harmful. • Soil bacteria decomposes dead plants and animals so that their nutrients are added to the soil in a useable form for growing plants. Without these soil bacteria, the soil would lack usable fertilizer. • Bacteria is also used to make alcoholic beverages, vinegar, buttermilk, cheese, and yogurt. Other bacteria eat crude oil and are used to clean up oil spills.
How Do Bacteria Cause Disease • They can enter a person who acts as a host • They can reproduce in the host • They can act adversely on the tissue in the host by producing harmful bi-products during cellular respiration • Examples of bacterial diseases that affect people are; tetanus, typhoid fever, pneumonia, meningitis and black plague • Bacteria produce about every 20minutes. It is estimated that if unlimited food and space was available a single bacterium after two days of reproduction would reach the mass of about 4000x the mass of the earth!
Toxins Exotoxin Endotoxin -released into the sorrounding of bacteria Inhibit protein synthesis Damage cell membranes and interfere with normal nerve functioning -is a lipid toxin formed from the cell wall Released only when the infected cell reptures. Toxic only at high doses Resists body’s defence system more than exotoxins Symptoms are high fever and diarrhoea.
Infectious diseases/communicable diseases/contagious diseases / transmissible diseases Transmission of pathogen can occur in various ways -physical contact -contaminated food -body fluids -airborne inhalation -through vector organisms
Viruses: • are associated with a number of plant, animal, and human diseases • can only reproduce by using the metabolic machinery of the host cell (obligate intracellular parasites) • are non‐cellular pathogens • may have a DNA or RNA genome • Nucleic acid is enclosed by a protective protein coat or capsid • Bacterial virus are called bacteriophage.
Viral Mutations • Viruses often mutate; therefore, it is correct to say that they evolve. • Those that mutate are troublesome; a vaccine effective today may not be effective tomorrow. • Influenza (flu) viruses mutate regularly.
Viroids and Prions • Viroids are naked strands of RNA, a dozen of which cause crop diseases(plant pathogen). Like viruses, viroids direct the cell to produce more viroids. • Prions(proteinaceous infectious particles) are newly discovered disease agents that differ from viruses and bacteria. – Prions are rogue proteins with a wrongly‐shaped tertiary structure that cause other proteins to distort.
Eukaryotic pathogens Single celled • Amoeba Multicellular (exoparasites or endoparasites) • Worms(ring worms, tape worms...) • Pathogenic fungus
Antibiotics • A broad-spectrum antibiotic acts against many different kinds of disease-causing bacteria, including both gram-positive and gram-negative bacteria. A narrow-spectrum antibiotic acts only against specific families of bacteria. • NARROW SPECTRUM ANTIBIOTICS:are used for the specific infection when the causative organism is known.
Control against pathogens • -Quarantine control measures • -Vaccination • Hygene practises
