LECTURE 1 Flashcards
What is Microbiology?
A great complex of biological sciences about micro-organisms
What are the major groups of microorganisms?
- Bacteria
- Archaea
- Fungi
- Algae
- Protozoa
- Viruses
What are the different types of Human pathogens?
SUBCELLULAR BIOLOGICAL ENTITIES:
- Prions (infection proteins)
- Viruses
PROKARYOTIC MICROORGANISMS:
- Chlamydiae
- Rickettsiae
- Mycoplasmas
- Classic bacteria
EUKARYOTIC MICROORGANISMS:
- Fungi
- Protozoa
ANIMALS:
- Helminths
- Arthropods
What did Antony van Leeuwenhoek do?
- First person who observed and described microorganisms
- Constructed first microscope (magnification 50-300X)
What did Louis Pasteur do?
- Established that fermentation was the result of microbial activity
- Introduced techniques of sterilisation
- Showed that microorganisms DO NOT arise by spontaneous generation
- Elaborated methods of pathogenic microorganisms attenuation
- Developed rabies vaccine and anthrax one
What are the key concepts of Koch’s postulates?
- A specific infectious disease is caused by a specific microbe
- Postulates help determine the ETIOLOGY of disease (first step in treatment + prevention)
What did Robert Koch do?
- Elaborated methods of staining and cultivation of microorganisms
- Discovered what caused anthrax, cholera and tubercle bacillus
- Proposed techniques for pure culture isolation
- Elaborated criteria for proving relationship between a microorganism and specific diseases (Koch’s postulates)
What are Koch’s postulates?
- Microorganisms must be present in every case of the disease but absent in healthy organism
- Suspected microorganism must be isolated and grown in pure culture
- Same disease must result when the isolated microorganism is inoculated into a healthy host
- Same microorganism must be isolated again from the diseased host
What are the different characteristics of the different Bacterial forms?
- COCCI: occur in clusters, chains, pairs and packets
- STRAIGHT RODS: uniform thickness, rounded/pointed ends
- CURVED RODS: comma shaped, spiral, screw shaped
- MYCOPLASMAS: bacteria without a rigid cell wall, coccoid cells, long threads
- CHLAMYDIAE: either spherical/oval elementary bodies or spherical/oval reticulate bodies
- RICKETTSIAE: short coccoid rods
Which structures are found in all bacteria?
- Plasma membrane
- Cytoplasm
- 70S Ribosomes
- Nucleoid containing DNA
____________ of bacterial flagella propel the cell through an aqueous environment
Rotation
What is the difference between a Nucleoid and a Plasmid?
Nucleoid = Double-stranded DNA localised in the cytoplasm
Plasmid = Genetic structure with circular DNA
Describe the formation of endospores by sporulation
1) Spore septum isolates newly replicated DNA and a small portion of cytoplasm + Plasma membrane surrounds isolated DNA and cytoplasm
2) Spore septum surrounds isolated portion forming FORESPORE
3) Petidoglycan layer forms between membranes, spore coat forms and Endospore is freed from cell
What does the cytoplasm contain?
- A large number of solute low and high molecular weight substances
- RNA
- 20000 ribosomes
- Reserve substances (e.g glycogen depots, polymerised metaphosphate, lipids)
Bacteria have _____ ribosomes comprising 30S and 50S subunits
70S
What are the Bacterial cell wall functions?
- Protect the PROTOPLASTS from EXTERNAL NOXAE
- Withstand and maintain the osmotic pressure gradient between the cell interior and the extracellular environment
- Give cell its outer form + facilitate communication with its surroundings
What gives the bacterial cell wall its strength?
A layer composed of a substance referred to as Murein, Mucopeptide or Peptidoglycan
Explanation: Consists of repeating units of N-ACETYLGLUCOSAMINE (NAG) and N-ACETYLMURAMIC ACID (NAM) crossed linked by peptide side chains. PENICILLIN-BINDING PROTEINS (PBP) cross-link these peptide side chains
What are the characteristics of Gram-positive bacteria?
- Thick murein layer
- Proteins and trichroic acids anchored in the murrain
- Lipoteichoic acid fixed to membrane by lipophilic anchor
- No Porin proteins or Periplasm
- More sensitive to penicillin and lysozyme
What are the characteristics of Gram-negative bacteria?
- Thin murein layer
- Outer membrane connected to murein layer by proteins (OmpA, murein lipoprotein)
- Outer layer made up of closely packed lipopolysaccharide complexes (aka “endotoxin”)
- Porin proteins and Periplasm present
- Not sensitive to penicillin and lysozyme
What does the Lipopolysaccharide complex consist of?
- Lipid (Diglucosamine, Fatty acids & phosphate)
- Core polysaccharide (Inner & outer core region of different sugars)
- O-specific polysaccharide chain (Repeating units consisting of 3-8 sugars)
What colour do Gram-positive and Gram-negative bacteria stain?
Gram positive = Purple
Gram negative = Reddish-pink
What are the factors that affect the growth of bacteria?
- Nutrition
- Oxygen
- Carbon dioxide
- Temperature
- Moisture and drying
- Light
- H+ ion concentration
- Osmotic effect
Macrophages produce Hydrogen peroxide, Superoxide radicals and Hydroxyl radicals to pour over bacteria. What are the three enzymes bacteria possess to break down these oxygen products?
- CATALASE (breaks down hydrogen peroxide into water + oxygen)
- PEROXIDASE (breaks down hydrogen peroxide)
- SUPEROXIDE DISMUTASE (breaks down superoxide dismutase into hydrogen peroxide + oxygen)
What are the steps of Binary Fission?
1) DNA replication
2) Cell elongation
3) Septum formation
4) Completion of septum with formation of distinct walls
5) Cell separation
What are the growth phases of Bacterial populations?
1) LAG PHASE (preparation for population growth + no increase)
2) LOG PHASE (exponential increase in population)
3) STATIONARY PHASE (microbial deaths balance production of new cells)
4) DEATH PHASE (exponential decrease)
Define Prototrophic, Chemotrophic, Autotrophic and Heterotrophic
Prototrophic = deliver their energy from sunlight
Chemotrophic = obtain energy from chemical reaction
Autotrophic = synthesise all their organic compounds
Heterotrophic = unable to synthesise their own metabolites
What are the different sterilisation techniques?
- Heat
- Filtration (cellulose-acetate membrane filters)
- Chemicals (ethylene oxide = plastic dishes and pipettes, beta-propiolactone = living tissues)
- Radiation
Explanation: Sterilisation is the killing of all microorganisms and viruses or their complete elimination from a material with the highest possible level of certainty
What is the difference between disinfection, preservation and decontamination?
Disinfection = antimicrobial treatment that prevents transmission of microorganisms
Preservation = prevents microbes caused by spoilage of susceptible products
Decontamination = removal or count reduction of microorganisms contaminating an object
What is the difference between Aseptic and Antiseptic measures?
Aseptic measures = prevents microbial contamination of materials or wounds
Antiseptic measures = chemical agents used to fight pathogens in or on living tissue
What is the mechanism of action of ionising radiation, Uv light and chemical agents?
- Ionising radiation = form reactive groups -> chemical reactions -> affect DNA and proteins
- UV light = structural changes in DNA that prevent it from replicating
- Chemical agents = attack cytoplasmic membrane
What are the two types of Ionising radiation used?
- Gamma radiation = electromagnetic waves produced by nuclear disintegration
- Corpuscular radiation = electrons produced in generators and accelerated to raise their energy level
Which disinfectants are considered “low level”?
- Quaternary ammonium compounds (inactivates enzymes/denatures proteins + bacterial, fungicidal but not sporocidal)
- Phenols (inactivates enzymes, leaks cell wall + fungicidal, bactericidal, but not sporocidal)
- Guanidine derivatives (Protein denaturation, not sporocidal)
- Alcohols (Protein denaturation + bactericidal, fungicidal, not sporocidal)
- Chlorine/Hypochlorite (Protein denaturation, inactivates nucleic acids + fungicidal, bactericidal and sporicidal)
Which disinfectants are considered “High level”?
- Aldehydes (Alkylation of amino groups of proteins + bactericidal, fungicidal and sporocidal)
- Glucoprotamin (Denaturation of proteins + bactericidal, fungicidal, virusidal, not sporicidal)
- Peroxides/Paracetic acid (Effects DNA lipids + fungicidal, bactericidal, sporocidal)
What are the different ways of verifying sterilisation?
- Airsampling (ACTIVE, Quantitative, disruption of airflow)
- Surface sampling/settle plates (PASSIVE, semi-quantitative, inexpensive, minimal disturbance)
- Swabs
- Indicator strips
What happens in a compound microscope?
The image from the objective lens is magnified again by the ocular lens
TOTAL MAGNIFICATION = OBJECTIVE LENS X OCULAR LENS
Describe Basic stains
- DYES = Methylene blue, Crystal violet, Safranin
- PURPOSE = Stain negatively charged molecules and structures (e.g nucleic acids + proteins)
- OUTCOME = +ve stain
Describe Acidic stains
- DYES = Eosin, Rose Bengal, Acid fuchsin, Congo red
- PURPOSE = Stain positively charged molecules and structures (e.g proteins)
- OUTCOME = can either be a +ve or -ve stain depending on the cell’s chemistry
Describe Negative stains
- DYES = India ink, Nigrosin
- PURPOSE = Stains background, not specimen
- OUTCOME = Dark background with light specimen
What are special stains used to colour?
- Endospores
- Flagella
- Capsules
What is the difference between Gram stain and Acid-Fast stain?
Gram Stain = Gram +ve vs Gram -ve
Acid-Fast Stain = Used to identify acid-fast bacteria with a waxy, lipid cell wall
What happens in the Slide agglutination test?
1) Samples of an unknown bacteria are placed in a drop of saline on several slides + different known antiserum is added to each sample
2) Bacteria agglutinate when mixed with antibodies that were produced in response to that species or strain of bacteria
3) Positive test indicated by presence of agglutination
What is Flow Cytometry and was does it entail?
Flow Cytometry = identifies bacteria in a sample without culturing bacteria
1) A moving fluid containing bacteria is forced through a small opening
2) Fluid passing through is illuminated by a laser
3) Scattering of light provides info about cell size, shape, density and surface -> analysed by computer
What is DNA Fingerprinting?
A technique that chemically divides DNA into fragments which form unique patterns, used to determine specific organisms
What is DNA Base Composition used for?
Gives conclusion about relatedness of the bases
What is Nucleic Acid Amplification Tests?
Used to increase the amount of microbial DNA to levels that can be tested by gel electrophoresis
