CHAPTER 1 The Background of Microbiology 1-2

Introduction Health care workers are at risk for occupational exposure Hippocrates-Greek physician-known as father of medicine Ignaz Semmelweis-discovered hand washing and relation to decrease deaths due to infections Louis Pasteur-germ theory Joseph Lister-discovered that infection could be prevented if dressings with antiseptic were used 1-3

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)-less complex Eukaryotes (e.g., animals, plants)-more complex 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 Nucleus Outer layer; selectively permeable Protects; provides passage for nutrient/waste Nucleus Control center Contains DNA 1-8

Eukaryotes Cytoplasm Nucleolus Ribosomes Maintains cell shape Within the nucleus Needed for protein manufacture Ribosomes Site of protein synthesis Contain RNA 1-9

Eukaryotes Mitochondria Golgi apparatus Lysosomes 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 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 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