microbiology

• Microbiologists study microscopic life forms and processes, including bacteria, algae, fungi, and some parasites and their vectors
• Microbiologists aim to solve health, environmental, climate, and food and agriculture problems by understanding microbes
• Micro-organisms include bacteria, fungi, protoctista, and viruses
• Bacteria and fungi decay dead organisms, releasing and recycling nutrients
• Some bacteria are pathogens and cause disease, while others are beneficial
• Bacteria reproduce asexually by binary fission
• The human body contains approximately one hundred trillion bacteria
• Bacteria can be distinguished by their size, shape, staining characteristics, metabolic features, antigenic features, and genetic features
• Bacteria sizes vary but are usually 1-10 µm in length
• Bacteria can be classified by shape: Coccus (spherical), Bacillus (rod-shaped), Spirillum (spiral/comma/corkscrew)
• Bacteria can be classified by metabolic features and antigenic features
• Gram staining technique distinguishes between Gram positive and Gram negative bacteria based on cell wall composition
• Gram positive bacteria have a thick peptidoglycan cell wall and appear purple, while Gram negative bacteria have a thin peptidoglycan cell wall and appear red
• Bacteria can undergo binary fission and reproduce quickly in suitable environments
• Bacteria require specific conditions for growth including pH, oxygen requirement, temperature, and nutrients
• Obligate aerobes require oxygen, obligate anaerobes cannot survive with oxygen, and facultative anaerobes can survive with or without oxygen
• Clostridium perfringens are obligate anaerobes that grow in wounds and produce toxins causing gas gangrene
• Bacteria can use different substrates for respiration and release energy to synthesise ATP
• Aerobic and anaerobic respiration have similarities in glycolysis but differ in the final electron acceptor
• Tubes can represent cultures of obligate anaerobes, facultative anaerobes, and obligate aerobes based on oxygen requirements
• Glycolysis produces 2 ATP and 2 NADH/H+
• Alcoholic fermentation and aerobic respiration both produce CO2
• Differences between aerobic respiration and anaerobic respiration:

  • Aerobic respiration uses O2 as the final electron acceptor, but anaerobic respiration does not
  • Aerobic respiration includes the link reaction, Krebs cycle, and ETC (oxidative phosphorylation) inside mitochondria, while anaerobic respiration does not
• Different substances and their pathways:

  • Glucose enters glycolysis
  • Fatty acids convert to acetyl-CoA that enters the Krebs cycle
  • Glycerol enters glycolysis as triose phosphate
  • Amino acids enter the Krebs cycle
• Aseptic techniques:

  • Purpose: prevent contamination of pure culture by microbes from the environment
  • Sterilize all media and equipment before use
  • Handle cultures carefully, flaming the neck of culture bottles before opening and closing
• Sterilization methods:

  • Plastic equipment sterilized by gamma irradiation before use
  • Autoclave preferred method for sterilizing glassware and metal equipment
  • Autoclave process: sealed vessel, heated to 121°C in steam under high pressure for 15 minutes
• Measuring microbial growth:

  • Importance of estimating population growth
  • Methods: directly counting cells (total cell count, total viable count) and indirectly measuring turbidity
• Directly counting cells:

  • Plating and counting colonies
  • Serial dilution technique for total viable count
  • Inaccuracies in serial dilution: under-dilution leads to clumping, over-dilution results in too few colonies for accurate counting
• Indirectly counting cells:

  • Turbidimetry measures turbidity of culture as cell numbers increase
  • Colorimeter used to measure absorbance for total cell count
• Prokaryotae is the Kingdom that bacteria are found in
• Different shapes of bacteria include:

  • Coccus: a spherical bacterium
  • Spirillum: a spiral-shaped bacterium
  • Bacillus: a rod-shaped bacterium
• Gram positive bacteria stain purple due to crystal violet, while gram negative bacteria stain red due to safranin
• Peptidoglycan is the only component of a gram positive bacterial cell wall
• Lipopolysaccharide is a layer of the cell wall found only in gram negative bacteria
• Binary fission is the process by which bacteria divide
• Different types of bacteria based on oxygen requirements:

  • Obligate aerobe: can only survive and metabolize in the presence of oxygen
  • Obligate anaerobe: can only survive and metabolize in the absence of oxygen
  • Facultative anaerobe: prefer to metabolize in the presence of oxygen, but can metabolize in the absence of oxygen
• Aseptic technique is the process by which apparatus and equipment are kept free of microorganisms
• Autoclave is a sealed vessel in which glass and metal equipment are heated to 121°C at high pressure to sterilize them
• Total cell count is the total number of living and dead cells in a bacterial sample
• Total viable count is the total number of living cells in a known volume of liquid medium