MICRO 106 FINAL EXAM NOTES CLASS NOTES INTRODUCTION TO INFECTIOUS DISEASE 4 11 14 Most microbes don t cause disease Either non pathogens or due to host immunity Microbes are non pathogenic and are essential to There are more microbial cells than human cells on a human health healthy human Normal Microbial Flora 1 Microbial population of humans All parts of the human body in contact with external environment are heavily colonized by microbes e g skin mouth More microbes in moist regions armpits groin 2 Internal organs tissues free of microbes sterile 3 Relationship between humans and microbes mostly positive or neutral 4 Different microbes fungi and bacteria occupy distinct sites of the body Composition also changes over time and depending on environment 5 Prevent infections by out competing or inhibiting growth of opportunistic and actual pathogens Definitions A Infection relationship between microbe and host 1 Competition between host and microbe may result in disease or resistance e g normal microbial flora infect body without causing disease B Pathogen disease causing parasite C Opportunistic pathogen normally non pathogens become pathogenic in an immunocompromised host e g Staph epi and other normal microbial flora D Virulence degree of pathogenicity e g Lactobacilli are avirulent Thyphoid bacillus is virulent Definitions Con t E Disease state of abnormal health 1 Endemic constant presence and limited spread in population measles 2 Epidemic rapid and widespread within population flu 3 Pandemic worldwide spread AIDS F Carrier individual who has recovered from disease but remains infectious Transmission of disease A Two methods direct and indirect B Direct contact 1 Requires physical contact between 2 hosts Handshakes common cold Aerosols common cold measles Sex herpes gonorrhea C Indirect contact 1 Contact with contaminated water food or fomites inanimate object e g syringes needles etc Ex insect or arthropod vectors mosquitoes and malaria yellow fever ticks and Lyme s disease Ex water typhoid cholera polio Ex food staph and E Coli food poisoning Ex needles hepatitis AIDS Establishment of disesae Site at which pathogen enters host Tetanus bacillus introduced into anaerobic tissue is dangerous A Portal of entry Harmless if eaten B Dose Number of cells introduced into host Varies dependent on pathogen and portal of entry E g salmonella few needed to get sick cholera need high numbers to get disease Establishment of disease con t C Invasiveness Ability to penetrate tissues and cause damage E g pathogenicity of virulent vs avirulent E Coli Depends on enzymes collagenase D Production of enzymes E g coagulase production by pathogenic Staphylococci and resistance to phagocytosis S aureus is pathogenic and coagulase positive S epi is coagulase negative and non pathogenic E Production of toxins Two types of toxins exotoxins and endotoxins Exotoxins are all proteins heat sensitive and dangerous at low concentrations Endotoxins part of gram negative cell wall heat resistant and dangerous at high concentrations CANNOT get endotoxin poison with staph infection Non specific resistance to disease Two parts to immune system Innate non specific immunity same response to all pathogens Adaptive specific immunity selective response Mechanical Chemical Cellular Biological Non specific resistance comprises barriers to infection Mechanical and Chemical barriers First line of defense interface w external environment Skin Protective barrier to infection Best source of protection Tough shell of keratinocytes Regular shedding from body releases attacked microbes Slightly acidic PH Salty Low water content Mucus membranes Moist epithelial linings secrete mucus Mucus traps microbes In respiratory tract ciliated epithelium moves trapped microbes into mouth spit or swallow Low PH of stomach and vaginal tract Lysozyme secretion destroys peptidoglycan layer of cell wall penicillin Defensins antimicrobial polypeptides produced by many host cells Destroy integrity of bacterial plasma membranes Biological barriers and immune response mechanisms Biological barriers Phagocytosis Destruction of microbe by phagocytic white blood cells e g macrophages neutrophils Immune response mechanisms Inflammation Characterized by redness swelling warmth pain Attracts white blood cells to sites of infection Destruction of microbes leads to pus formation IMMUNE RESPONSE MECHANISMS CON T 4 16 14 Immune response mechanisms Fever Interferons Induced by pyrogens which can be exogenous e g bacterial toxins or endogenous produced by host cells in response to infection Higher body temperatures slows growth of pathogens Chemicals produced by cells in response to intracellular infection Include antiviral responses in uninfected cells Also activate white blood cells Recognize and destroy cells infected with intracellular pathogens as well Natural killer NK cells as cancerous cells Complement cascade Antibacterial blood proteins Insert pores into microbial membranes Specific resistance and the immune system Overview invaders lymphocytes Response by sub set of white blood cells to individual pathogens or Main features of specific resistance recognize respond remember Discriminates between self and non self cells tissues Key cell type involved white blood cell known as lymphocytes Two types B and T cells Two branches of specific immunity Humeral immunity B cell antibody dependent attacks extracellular pathogens Cell mediated T cell dependent attacks intracellular pathogens Antigens Ag s Antibody generator Also known as immunogens Substances to which lymphocytes respond Most antigens not usually found in the body e g toxins bacterial cell wall pili Most potent antigens are proteins some antigens are carbs Many antigens are large and need to be processed by macrophages Antigens digested into smaller pieces are known as epitopes Macrophages present epitopes to the lymphocytes In a healthy human body s own proteins or chemicals are non immunogenic Recognized as self Occasionally systems break down self tissues attacked by immune system Autoimmune disease e g Lupus Rheumatoid arthritis SPECIFIC RESISTANCE AND THE IMMUNE SYSTEM 4 18 14 Specific resistance and the immune system Con t Origin of immune system Starts to develop 2 months in utero Lymphocytes arise from bone marrow stem cells Some stem cells migrate to thymus gland to give rise to T cells Involved in cell mediated immunity CMI Within thymus gland self recognizing T cells are eliminated