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30 Cards in this Set
- Front
- Back
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Microorganisms defined as ?
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Organisms or agents which cannot be seen with naked eye (<1mm) although some fungi and algi can be seen.
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Microrganisms of medical importance include?
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• Bacteria.
• Viruses. • Protozoa. • Algae. • Fungi. • Multicellular parasites. |
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Which microorganisms can be seen by 1, electron microscope, 2 light microscope, 3 naked eye?
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• PIC: RELATIVE SIZE OF MICRORGANISMS (Poliovirus smallest: electron microscope, all others except louse (naked eye): light microscope, fungal spores and protozoa biggest of light microscope group)
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Structure of bacteria?
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• All free-living prokaryotes.
• Prokaryotes possess simple unicellular structure (plasma membrane enclosing cytoplasm usually bounded by a cell wall). • Absence of nuclear membrane and discrete organelles (compare eukaryotes). • Cytoplasm-featureless granular mass. • Cytoplasm contains DNA (usually circular dsDNA) localised in nucleoid region and may be plasmids (small circular DNA). BACTERIA • Ribosomes scattered in cytoplasm. • Cytoplasmic inclusion bodies (nutrient reserves). • External structures include flagella (motility) and hair like appendages (fimbriae and pili). • May be an external layer to the cell wall (glycocalyx, capsule, slime layer). • Majority possess one of three common shapes (coccus, bacillus or spirillum). BACTERIAL CELL WALL • Semi-rigid structure present in most bacteria lying outside the plasma membrane. • Principal component is peptidoglycan. • Most bacteria can be classified into two major groups based on cell wall composition (Gram-positive and Gram-negative). |
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Feautures of gram positive bacteria?
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• Gram-positive cell wall characterised by a thick peptidoglycan layer and possess complex polysaccharides called teichoic acids.
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Features of gram negative bacteria?
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• Gram-negative cell wall possesses a thin peptidoglycan layer bounded by an outer membrane.
• Gram-negative outer membrane contains lipopolysaccharide (LPS). • LPS contains endotoxin (causes toxic effects in Gram-negative infections). |
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Media bacteria may be grown in?
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• Bacteria may be grown in a wide variety of different media in the laboratory (defined, complex, enriched, selective, differential).
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Factors affecting bacterial growth?
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• Physical factors include temperature, pH (optimum close to neutral for most bacteria), oxygen (aerobic (obligate) or anaerobic (obligate, facultative)), water and osmotic pressure (isotonic (optimal), hypotonic (lysis), hypertonic (shrinking)).
• Culture media provide nutritional factors, stable pH and isotonic environment. |
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Which 3 bacteria cannot be grown in media?
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Mycobacterium leprae, Treponema pallidum, Chlamydia.
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What is the "generation time" in bacterial growth?
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The time taken to reproduce (ecoli 20 mins mycobacteria hours)
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What are the four phases of bacterial growth and what do they involve?
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lag (making copies)
exponential (reproduce by binary fission log not linear scale) stationary (no food left) decline |
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How are pure cultures obtained?
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PURE CULTURES
• Liquid media may be used initially to increase the number of bacteria in the sample (blood, anaerobes)-many grow overnight (15-18 hours). • Follow with culture on solid media (agar) in a Petri dish. • Various methods to prepare pure cultures (spread plate, pour plate and streak plate). • Streak plate method commonly used (cell mixture in a 3-4 way steak on agar). |
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What is presumptive identification of bacteria based on?
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• Usually based on:
• Gram stain-most bacteria stain Gram-positive (purple) or Gram-negative (pink). • Other stains (flagella, capsule, acid fast). • Cell and colony morphology. • Aerobic, anaerobic growth (or both). • Specialised nutritional requirements for growth. |
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Features of bacterial morphology?
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• Most range in size from 1-10m in length and 0.2-1m in diameter (some exceptions).
• Three principal shapes-spheres (cocci), rods (bacilli) and spirals (spirilli) and may possess flagella. • May grow in chains or clusters. |
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4 other ways (greater specifity) to identify bacteria?
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• Serological tests-implies the detection of microorganisms by specific antibodies.
• Molecular techniques-detect nucleic acids fragments (PCR, nucleic acid hybridisation). • Biochemical tests-battery of biochemical tests (metabolic products including enzymes, sugars, alcohols and acids). • Resistance or susceptibility to antibiotics. |
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Structure of viruses?
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• Virions all consist of nucleic acid genome surrounded by protein capsid (nucleocapsid).
• Capsids assemble spontaneously from basic subunits and occur in distinct shapes (helix, icosahedron). • Some viruses possess envelopes (usually lipid bilayer derived from host cell). • Non-enveloped viruses referred to as naked viruses. |
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Capsid characteristics?
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• Require little genetic input for construction.
• May possess distinctive antigenic structure. • Involved in the attachment and entry of virion into a host cell. • Protect viral nucleic acid. • Resistant to desiccation, pH change and detergents (naked viruses). • May be used in identification. |
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Viral envelopes & what is a peplomere?
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• Outer membranous layer surrounding the nucleocapsid.
• Normal host cell constituents but proteins virally encoded. • Proteins may project as spikes (peplomers) from the envelope. • Spikes involved in attachment of virus to host cells. • Determine antigenic characteristics. |
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How are viruses classified?
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• At present separated into major groups or families based on size, morphology, type of nucleic acid and mode of replication.
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How many DNA virus families are there? How many RNA?
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• DNA viruses associated with human disease fall into seven families.
• RNA viruses associated with human disease fall into at least 15 families. |
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What does the host cell provide in viral replication?
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• Host cell provides substrates, energy and hardware.
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What are the six steps in viral replication?
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• Adsorption-attachment to host cell receptor.
• Penetration-direct, membrane fusion, phagocytosis. • Uncoating-nucleic acid released into cytoplasm. • Synthesis-copy nucleic acid many times (type of nucleic acid). • Assembly-DNA viruses in nucleus, RNA viruses in cytoplasm. • Release-naked viruses usually result in cell lysis, enveloped viruses ‘bud’. |
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How are most viruses diagnosed?
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signs and symptoms
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What are three virus identification techniques?
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serology,
molecular techniques cell/tissue culture methods. |
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Virus identification how are the propagated
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• Viruses obligate intracellular parasites.
• May be propagated in animals (in vivo), embryonated eggs and cell/tissue culture (in vitro). • Cell culture methods commonly used and many viruses (not all) produce cytopathic effects (CPE) in the cells they infect. |
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What are cytopathic effects? (CPE)
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CPE viewed microscopically and is often typical of infecting virus and include:
• Appearance of inclusion bodies. • Generation of syncytia. • Morphological changes such as the occurrence of spindle-shaped cells. • Cell death (plaques). |
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Features of protozoa and algae?
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• Unicellular eukaryotes (nucleus and other organelles).
• Mainly aquatic. • Protozoa do not possess chlorophyll but algae do. • Relatively few protozoa cause human disease (Amoebae, Giardia, Cryptosporidium, Plasmodium). • Algae do not cause infectious disease but do produce toxins. |
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Feautures of fungi? (5)
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• Diverse group of unicellular and multicellular eukaryotes.
• Possess a cell wall. • Very few pathogenic in man (yeasts and filamentous fungi). • Principally opportunistic pathogens. • Most fungal infections (mycoses) are cutaneous. • Systemic mycoses are life-threatening. |
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features of multicellular parasites?
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• Endoparasites-include the helminth worms (flatworms and roundworms).
• Have microscopic stages in their life cycles and are usually classed as microbial diseases. • Ectoparasites-include the fleas, ticks, lice and mites (form a parasitic relationship on the outside surface of the human body). • May also act as vectors for microorganisms. |
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Feautures of prions?
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• Prion is a protein that is a protease-resistant isoform (PrPres) of normal brain protein (PrPc).
• Prion protein initiates a conformational change in the brain protein and brings about disease. • Disease is result of accumulation of abnormal protein in brain resulting in vacuole formation. • These unusual neurodegenerative disorders are called transmissible spongiform encephalopathies. |
