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Transcript
1-1 CHAPTER 1 The Background of Microbiology 1-2 Introduction • Microbiology: study of organisms that cannot be seen by gross examination • Microscope is needed • Three types of microscopes – Basic compound microscope – Scanning electron microscope – Confocal laser microscope (Continues) 1-3 Introduction • Microorganisms – Abundant in/on the body – Many are beneficial (normal flora) – Few cause disease (pathogenic) – Increased ability to produce an infection (virulence) 1-4 Classifications of Microorganisms • According to cell type – Protists (one-celled organisms) • Two groups Prokaryotes (e.g., bacteria, mycoplasmas) Eukaryotes (e.g., animals, plants) (Continues) 1-5 Classifications of Microorganisms • Unclassified microorganisms include – Viruses • Incapable of reproducing on their own • Require a host cell • For example, measles, HIV, common cold 1-6 Infectious Proteins • Prions – Do not fit any cellular category – Anucleate – Cause CNS infections – Lack nucleic acid 1-7 Eukaryotes • Cell membrane – Outer layer; selectively permeable – Protects; provides passage for nutrient/waste • Nucleus – Control center – Contains DNA (Continues) 1-8 Eukaryotes • Cytoplasm – Maintains cell shape • Nucleolus – Within the nucleus – Needed for protein manufacture • Ribosomes – Site of protein synthesis – Contain RNA (Continues) 1-9 Eukaryotes • Mitochondria – Powerhouses – Store energy in the form of ATP • Golgi apparatus – Combines CHO with proteins • Lysosomes – Synthesized in ER 1-10 Prokaryotes • Contain – Cell membrane, cell wall – No nucleus (anucleate) – Nucleoid for storing DNA – Capsule of slime layer to increase resistance to antibacterial agents (Continues) 1-11 Prokaryotes • Cilia (short, fine filaments that move fluid over a surface) • Flagella (long filaments that provide motility for the cell) • Spores (hard outer wall produced by inactive bacterial cells) 1-12 Normal Flora versus Pathogens • Normal flora – Exist on, in, or around us; may become pathogenic if they do not remain in intended location of the body – Most prevalent in areas open to the outside – Not found in blood or CSF • Pathogen – Capable of causing disease 1-13 Immune System • Three lines of defense – Protective barriers – Circulatory or bloodstream response – Innate, adaptive response 1-14 Protective Barriers • • • • Intact skin and its secretions Respiratory tract (e.g., mucus, sneezing) GI tract (e.g., saliva, acidic pH of stomach) GU tract (e.g., expulsion of urine) 1-15 Circulatory and Bloodstream Response • Phagocytes (phag/o = to eat) – Neutrophils, monocytes, macrophages, dendritic cells • Lysosomes – May be in fixed locations (e.g., bone marrow, liver) or may roam to location of foreign substance 1-16 Innate Immune Response • • • • • Exists at birth Is not pathogen specific Does not require previous exposure Kills invading microbes Begins inflammatory response (redness, swelling, and pain) • Alerts adaptive immune response 1-17 Innate/Adaptive Immune Response • Antigen presenting cells (APCs) – Macrophages and dendritic cells kill microbes – Present intruding microorganisms to T cells • Antigen – Marker recognized as foreign – Phagocytic cells engulf pathogen, presenting fragments on its surface, notifying the adaptive immune system of invader 1-18 Adaptive Immune Response • Cellular mediated – Recognizes pathogen – Activates T cells (which secrete cytokines) • Humoral response – T cells interact with B cells that produce antibodies (immunoglobulins) – Antibodies destroy antigen 1-19 Infection • Caused by invasion by microbe • Localized or generalized • Virulence determined by – Cell structure – Production of endotoxin (contained within the microbe) or exotoxin (produced by and secreted by the microbe) (Continues) 1-20 Infection • Most common disease-causing microorganisms in humans – Bacteria – Viruses – Fungi – Parasites 1-21 Direct and Indirect Disease Transmission • Contact transmission – Direct contact (with the person) – Indirect contact (with fomite, vector, common vehicle, or airborne droplets) 1-22 Fever and the Inflammatory Response • Infection accompanied by – Fever • Assists in clearing infections • Important defense mechanism – Inflammation • Part of the innate immune response • Caused by dilatation of blood vessels • Infiltration of infected site by antibodies and WBCs results in death of the microbe 1-23 Summary • Classification of microorganisms – Prokaryotic – Eukaryotic • Normal flora – Live on/in body • Pathogens – Cause disease (Continues) 1-24 Summary • Immune system response – Innate – Adaptive • Cellular • Humoral • Pathogenicity – Ability of microbes to cause disease • Virulence – Strength of disease-causing microbe 1-25