Microbial Growth
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  • 1. Unit 8034 Culture microorganisms and control microbial growth By Elysia Butler
  • 2. Nutritional Requirements
    • All living organisms require nutrients to grow.
    • Microorganisms get their nutrients in the form of chemical elements which exist in nature as either organic or inorganic compounds.
  • 3. Nutrients
    • Carbon – Used in the creation of proteins, carbohydrates and lipids.
    • Nitrogen – Utilised in amino acids, which make up proteins.
    • Hydrogen and Oxygen – Generally make up the organic compounds that are ingested or absorbed.
  • 4. Nutrients
    • Sulphur – Important with regards to amino acids.
    • Phosphorus – Important with regards to adenosine triphosphate and nucleic acids.
    • Other elements are also required for the nutrition of microorganisms but in smaller quantities.
  • 5. Hetero / Auto - trophs
    • Heterotrophs - Obtain the majority of their carbon as organic compounds by either directly absorbing it through the environment or by ingesting other heterotrophs or autotrophs.
    • Autotrophs -Obtain their carbon source as inorganic elements through the environment.
  • 6. Chemo / Photo - trophs
    • Chemotrophs – Obtain their energy from chemical compounds.
    • Phototrophs – Obtain the majority of their energy from a light source.
    • Some organisms cant be classified solely as a chemotroph or a phototroph as they have the ability to adapt to the surrounds eg R. rubrum
  • 7. Selective Media
    • Encourage growth of specific types of microorganisms
    • Inhibits growth of specific microorganisms
    • Sometimes used for both of the above purposes.
  • 8. Differential Media
    • Can grow more than one type of microorganism
    • Can compare one type to another
    • Varying appearance of microorganisms on the media
    • For example one type may react with the media and turn blue while another type may appear purple
  • 9. Differential Example
    • To the right is a photograph of different bacterium grown on differential media
    • E. coli - blue
    • E. aerogenes - purple
    • P.aeruginosa - yellow
  • 10. Limiting Microbial Growth Physically
    • Microbial growth can be limited by altering one or all of the following to a level that the organism will not thrive in;
    • Temperature
    • pH
    • Gaseous Atmosphere
    • Osmotic Pressure
  • 11. Temperature
    • Psychrophiles – organisms that grow best between 15C – 20C
    • Mesophiles – organisms that grow best between 25C – 40C
    • Thermophiles – organisms that grow best between 25C – 40C
    Above - Microorganisms can be classified based on the temperature at which they thrive
  • 12. Gaseous Atmosphere
    • Aerobic – Typically require oxygen at levels of 21%
    • Anaerobic – Don’t require oxygen
    • Faculative – Can grow both aerobically and anaerobically
    • Microaerophilic – Typically require oxygen at levels of 1 – 15%
    Above - Classification of microorganisms based on gaseous oxygen levels at which the microorganism can grow.
  • 13. Limiting Microbial Growth Chemically
    • Adding antimicrobial agents to media will inhibit the growth of specific organisms.
    • Example - Media to which Colistin and Nalidixic acid have been added will inhibit gram-negative bacteria growth but promote Gram-positive cocci growth.
  • 14. Iodine
    • Kills bacteria and endospores on human skin
    • Presence of organic material decreases effectiveness of iodine to kill endospores
    • Eliminate organic material to increase rate at which iodine will kill endospores
    • Mode of action: Damages metabolic compounds
  • 15. Formaldehyde Gas
    • Kills bacteria and endospores in enclosed areas
    • Kills vegetative cells quicker
    • To be effective temperature must be 22 °C
    • Humidity needs to be approximately 60-80%
    • Mode of action: Inactivates nucleic acids and proteins.
  • 16. Phenolic Compounds
    • Bacteriostatic (Inhibits growth but does not kill) at low concentrations
    • Bactericidal (Kills) at higher concentrations
    • Mode of action: Damages Cytoplasmic Membrane
  • 17. Antibiotic Mode of Action
    • Can work by affecting the Peptidoglycan in the Cell Wall
    • Inhibits crosslinks from forming in Peptidoglycan
    • Peptidoglycan loses rigidity
    • Causing cell to absorb water
    • Cell splits and dies
    • Penicillins and Cephalosporins - antibiotics that work by targeting the Cell Wall
  • 18. Antibiotic mode of action
    • Some antibiotics kill pathogens by affecting the Cytoplasmic Membrane
    • Alters the permeability of Phospholipids in the Cytoplasmic Membrane
    • Causes leaking of vital substances from the cell resulting in death
    • Polymyxins – antibiotics that work by targeting the Cytoplasmic Membrane
  • 19. Limiting Antibiotic Effectiveness
    • Mutant cells that are non-responsive to the antibiotic.
    • Wrong type of antibiotic used for the specific pathogen.
    • Cells passing on antibiotic resistance to other cells through genes.
    • Increased use of antibiotics increases the risk of antibiotic resistant pathogens forming.