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Microbiology

Eleana Landregan Biology English

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Microbiology

BACTERIA
- Prokaryotes with peptidoglycan which composes Gram-positive cell walls
- Anaerobic or aerobic
- 1 to 10um
- Chromosomes pulled apart by attachments to inner membrane
- External cell wall
- RNA and protein synthesized in the single compartment
- No organelles
- No endo or exo cytosis
- Rods or cocci
- BACTERIAL SPORE FORMATION
  - Gram-positive bateria in rod shape can produce spores
  - Spores are highly resistant to chemicals, desiccation and nutrient depletion
  - Heat resistant so can survive pasteurisation/cooking
  - Dormant but germinate when the environment is optimal
- BACTERIA ASSOCIATED WITH FOOD
  - Pathogenic bacteria: food poisoning
    - Gram negative rods (Enterobacteriaceae non-spore forming rods) E.G. E coli.
    - Gram negative rods (Pseudomonads)
    - Gram positive rods (Clostridia)
  - Cultured bacteria
    - Gram positive rods (Lactobactilli - found in yoghurt)
- BACTERIAL STRUCTURE AND THE GRAM STAIN
  - Three types of cell wall layers; Gram positive, Gram negative and Acid fast
  - GRAM STAIN
    - 1. Add bacteria to microscope slide
    - 2. Set and stain with Crystal Violet (only retained in Gram positive cell walls
    - 3. Wash and stain Iodine
    - 4. Wash and destain with Ethanol
    - 5. Counterstain with Safranin
- BINARY FISSION
  - Asexual
  - Genomic DNA replicates
  - Cell doubles its mass
  - In ideal growth conditions E. coli is capable of undergoing one cell cycle every 20 minutes
- CONTROLLING PATHOGENIC BACTERIA
  - Sterilisation
    - Complete destruction/elimination of all viable organisms
    - E.G. spores, sterile objects, heat, radiation, chemicals and physical removal of cells
  - Disinfection
    - Kills, inhibits or removes organisms that may cause disease
    - Vegetative microorganisms but not spores
    - Inanimate objects (not safe for living tissues)
  - Decontamination with biocides
    - Kills, inhibits or removes organisms that may cause disease
    - Vegetative microorganisms and potentially spores
    - Very strong
    - Used for inanimate objects, healthcare
EUKARYA
- 10 to 100um
- Anaerobic or aerobic
- Internal cytoskeleton
- Long linear DNA
- RNA synthesized and processed in nucleus; proteins synthesized in cytoplasm
- Endo and exo cytosis
- Chromosomes pulled apart by attachments to cytoskeletal components
- FUNGI
  - Three groups: Moulds, Yeasts and Mushrooms
  - Cell walls made of chitin
  - Fungal cell walls made of hyphae
  - Together these make a mycelium
  - Form branches
  - Can reproduce sexually or asexually- fungal spores
  - Yeast 'bud'
ARCHAEA
- Prokaryotes without peptidoglycan
VIRUSES
- Contains either RNA or DNA and replicates in cells
- Has an extracellular state
PRIONS
- Entirely protein
- No nucleic acids
- Infectious
- Causes disease in animals
- Currently not found in plants
MICROBIAL NUTRITION
- AUTOTROPHS
  - Capable of synthesising complex organic molecules from a simple non-organic molecules
- HETEROTROPHS
  - Use organic molecules such as carbon
GROWING MICROBES IN THE LAB
- OPTIMAL CONDITIONS
  - Nutrient source
  - Optimal temperature
  - Water availability
  - pH
  - Gaseous atmosphere
  - No antimicrobials (agent that kills microorganisms or stops their growth)
- CULTURE
  - 1. Nutrient source
    - Carbohydrate - sugars
    - Proteins/amino acids - meat/yeast extracts
    - Minerals/Vitamins
  - 2. Broth culture
    - Test tubes/bottles
  - 3. Solid media
    - Test tubes/bottles
  - Culture media can be formulated to:
    - Meet nutritional requirements of certain bacteria
    - Selectively grow bacteria, inhibit others
    - Be diagnostic
MICROBES
- MICROBIAL GROWTH IN LIQUID (broth)
  - When bacteria grow in a liquid broth the normally follow a standard pattern of growth
- MICROBES AND TEMPERATURE
  - High temperatures cause:
    - Membrane disruption
    - Protein denaturation
    - For every 10C increase in temperature the metabolic rate and growth rates approximately double
  - Low temperatures cause:
    - Adaptations to maintain membrane fluidity
    - Slow metabolic processes
    - Slow growth rates