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General Principles of Microbiology.docx

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General Principles of Microbiology Basic StructureVirusesconsist mostly entirely of nucleic acids a protein shell capsidEnter cells and divert the synthetic processesmicrosmallbiolifelogystudy of or science Immunology study of our protection from foreign macromolecules or invading organisms and our responses to themDifferent classes of organismsViruseschlamydia grow only in living cellsMycoplasma grow on nonliving mediaBacteria no separate nucleus unicellularParasitesSmall microscopic12 microns 1 mm1000 micronsAddress them by their proper names ie not germs bugs What are they made ofVirusesNucleic acid either RNA or DNAnever bothSurrounded by protein shell capsidAttach inject nucleic acid penetration highjack synthetic processes inside cells to make more viruses package get out while going is good What are they made ofBacteriaRigid cell wall to keep things in placeGenetic material circular chromosomeNo nucleus nucleoidBoth DNA and RNABinary fissionSome bacteria do not have a rigid cell wall and are more fragile ie MycoplasmasWhat are they made ofEukaryotesUnicellular and multicellular animals and plantsGenetic material is organized into a nucleusAre all bacteria badbiotechnology spoilage of foods bioremediation functional foods etcCan we live without bacteria Normal florathe good guys Resident versus TransientGItract colon is inhabited by anaerobes and coliformsSkin mostly coagulase negative staphylococciWhere should there be NO bacteriaWhat can they do for usprotection from invasive bad bacteriametabolism vitamin K immune stimulationThe ways in which normal flora are clinically important are1A healthy active normal flora will to some extent protect a person from infection by invasive organisms1The normal flora of the gut participates in the metabolism of the host In particular vitamin K is synthesized by certain microorganisms and if there are disturbances in the normal flora there may be secondary nutritional deficiencies1Disturbances in the ecology and balance of the normal flora may be produced by antibiotic therapy this is the basis of antibiotic induced diarrhoea2The normal flora is controlled by various host defences may result in some patients in infections caused by organism which are normally not pathogenic What protects us from the bad guysMechanical barriersskin saliva mucous tears hairs etcOther helpers includeantibodiescomplementA system of plasma proteins that work together to resist bacterial infectionimmune cells Tcells NK cells macrophagesimmune system cell mediated humoural How do the bad guys get inAdherenceToxin production destroys some of our defensesOpportunismCompromised host how does this happenbacteraemia versus septicaemia aemiablood crobial diseaseInteraction between microorganisms and the host us is continuous battleThey need to enterlivemultiplyIn order to enter they need to colonizeestablish and multiply inon body clinical infectiondisease can result when damage occurs to host contamination deposition without multiplicationClinical diseaseeasy to recognizeSubclinical infectionhard to diagnose no symptoms How do we measure how dangerous a bacteriavirusparasite isPathogenicity ability to produce diseaseVirulence relative capacity to cause damage ie the degree of pathogenicityOpportunistic do not normally cause disease but can do so when defense mechanisms breached or compromised Pathogenesis of infectious diseasesA pathogenic microorganism enters your bodytwo things happen1Microorganism invader tries to multiplyinvade and cause disease 2 event2Host tries to prevent 1Whether the invader wins or not is dependent on several factors Transmissioninhalation ingestion break in protective barrier direct depositpathogenicityinvasivenessadherence persistence avoidance of immune systemtoxigenicityability to make toxins How does a pathogen adhere to usA bacteria needs to adhere evade and invade the hostTools used to achieve these huge objectivessurface structures pili fimbriaecapsulesEnzymes Bacterial Infections and Host DefencesIn human health the normal flora bacteria function as a balanced ecosystem with multiple species at a site and no single organism predominating Mechanical BarriersA barrier to the invasion of deep tissues by bacteria Extensively colonized larger numbers of organisms AdherenceFirst requirement adhere to the host tissues and bacteria have developed specific mechanisms to achieve this Ligands bind to specific receptors on the mammalian cell surface PhagocytosisMacrophages and the blood neutrophil are capable of ingesting bacteria and killing themThese are very important defence against invasion by bacteria Phagocytosis depends for its initiation on the ability of phagocytic cells to attach and form a vacuole Host response is sometimes to produce antibodies to the capsule which modifies the surface of the capsule in a way that permits the phagocyte to take up the capsulated organism opsonizationToxinogenicityToxins are substances usually proteins secreted by bacteria with the hope to cause damageTwo classesExotoxinsexcreted by livingcellsspecific affinitiesthermolabilepotent
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