SBI 241 - week 2.docx

**SBI 241 -- week 2 notes** **Classes of microorganisms** - Bacteria - Viruses - Fungi - Protozoa - Parasitic worms **Healthcare acquired infections** - Direct - Droplet - Indirect - Airborne/aerosol - Vector-dependant - Faecal-oral **PROCESS OF INFECTION**\ Colon...

**SBI 241 -- week 2 notes** **Classes of microorganisms** - Bacteria - Viruses - Fungi - Protozoa - Parasitic worms **Healthcare acquired infections** - Direct - Droplet - Indirect - Airborne/aerosol - Vector-dependant - Faecal-oral **PROCESS OF INFECTION**\ Colonisation Infection Spread **FACTORS FOR INFECTION** - Mechanism of action - Infectivity - Pathogenicity - Virulence - Immunogenicity - Toxigenicity **Host Defences** **Classes of infectious microorganisms** - Viruses - Bacteria - Fungi - Protozoa - Helminths **Bacteria**  **Gram Staining** - Staining procedure in which a dye colours all bacteria a deep purple. Alcohol applied and washes off purple colour from SOME bacteria while others retain the colour. - This provides useful information on which antibiotics to choose - *[Gram positive bacteria]* -- have a thick layer of peptidoglycan, found in cells walls of bacteria - *[Gram negative bacteria]* -- Only has a thin peptidoglycan layer + outer membrane outside the cell wall **Bacterial Toxins** - *[Exotoxins]* -- Enzymes released during bacterial growth. Damages cell membranes, inhibit protein synthesis. [Immunogenic: antitoxin production] - *[Endotoxins]* -- Lipopolysaccharides from outer membrane of dead gram-negatives, released during cell lysis or destruction of the bacteria. Pyrogenic effects, septic shock. **Septicaemia** -- Refers to the presence of microorganisms in the blood. **Bacteraemia** = presence of bacteria in the blood causing failure of the body's defence mechanisms Symptoms of Gram-negative septic shock is produced by the release of endotoxins release of vasoactive peptides and cytokines that affect blood vessels + producing vasodilation = reduces blood pressure, caused decreased oxygen delivery and produces septic shock. **Obligate intracellular parasites** - Dependent on host cells - No metabolism - Permissive host cell - Usually a self-limiting infection **Viral replication** - DNA or RNA - Protein receptor-binding site - Viral DNA enters nucleus and is transcribed into mRNA - Clinical symptoms will reflect the alteration of the function of the infected cells like influenza virus binds to a receptor on respiratory epithelial cells = causes symptoms of an upper respiratory tract infection **Cellular effects of viruses** - Inhibition of host cell DNA, RNA or protein synthesis - Disruption of lysosomal membranes - Promotion of apoptosis - Transformation of host cells into cancerous cells **Fungi = either moulds or yeast** - Singled cell = yeast - Double cell = moulds Diseases caused by fungi are call mycoses Dermatophytes = fungi that invades the skin.  Infection control -- prevent and treatment **Vaccines** - Induction of long-lasting protective immune responses that will not result in disease in a healthy recipient. Vaccines could be either: - Attenuated organism - Killed/inactive organism - Extracts of Antigens - Toxins **Immune system** +-----------------------------------+-----------------------------------+ | **The lymphatic system** | **Circulatory system** | +===================================+===================================+ | - Tonsils | - Bone marrow -- where all | | | immune cells are formed. | | - Thymus gland | | | | - Lymphocytes/white blood cells | | - Lymph nodes | | | | - Phagocytic cells (white blood | | - Spleen | cells) | | | | | - Appendix | - Dendritic cells | | | | | | - Thrombocytes (platelets) | | | | | | - Complement proteins | +-----------------------------------+-----------------------------------+ **Types of immunity** *[Non-specific (innate)]* - Immunity that is present from birth. Eg. Blood cells, physical barriers, chemical and mechanical barriers *[Specific (acquired/adaptive)]* - Immunity that develops as a result to exposure to infectious organisms: - Humoral immunity or antibody mediated immunity (involves B cell actions) - Cell-mediated immunity (involves T cell actions) Immunodeficiency -- insufficient to protect the host - Clinical presentation -- development of unusual or recurrent, severe infections Autoimmunity -- misdirected against the body's tissues - Breakdown of tolerance -\> body recognises self-antigens as foreign Allergy -- exaggerated hypersensitivity response to environmental antigens - Clinical presentation -- watery eyes, vomiting, runny nose. \*severe reactions -- skin rashes, swelling of lips, tongue or throat, SOB, dizziness/fainting. \* **Inflammation** Occurs in response to tissue injury *[Purpose:]* - Prevent & limit infection & further damage - Initiate healing and adaptive immune response *[Characteristic changes:]* - Localised vasodilation & increased capillary permeability - Movement of WBC, complement and plasma proteins to site of injury.  **5 signs of inflammation** - Heat - Redness - Swelling - Pain - Lose of function **Mast cell** - Cellular bags of granules located in the loose connective tissues close to blood vessels. skin, digestive lining and respiratory tract - Activation: - Physical injury - Chemical agents - Immunologic processes LEADS TO =\> [Degranulation] and [synthesis] of lipid-derived chemical mediators **Phagocytosis** - Process which a cell ingest and disposes of foreign material **Neutrophils** - Most abundant white cells - Life span = 4-8 hrs in circulation & 4-5 days in tissues - Major defence against bacterial infection *[Diapedesis]* -- neutrophils & monocytes squeeze through the pores in the blood capillaries to enter tissues, moved by AMAEBOID-type of motion *[Chemotaxis]* -- neutrophils move towards the source of certain chemicals = chemo-attractants. - Bacterial or viral toxins - Degenerative products of inflamed tissue - Products of complement system *[Opsonization]* -- process by which bacteria are made visible for neutrophils to be ingested