chapter 4 micro

Page 1: Metabolic Processes

• Aerobic vs Anaerobic Respiration

  • Aerobic Respiration

    • Oxygen: Requires O2

    • ATP Production: High yield through substrate-level phosphorylation (SLP) and oxidative phosphorylation (OP)

    • Electron Acceptor: External

  • Anaerobic Respiration

    • Oxygen: Does not require O2

    • ATP Production: Medium yield through SLP and OP

    • Electron Acceptor: External

  • Fermentation

    • Oxygen: Does not require O2

    • ATP Production: Low yield through SLP

    • Electron Acceptor: Internal

• Key Distinction:

  • Fermentation ≠ Anaerobic Respiration

• True/False: Fermentation is a form of anaerobic respiration. (False)

  Page 3: Microbial Temperature Adaptations

• Figure 4.21: Temperature and Growth Response in Different Temperature Classes of Microorganisms.

• adaptations in proteins and membrane lipids, increased ionic bonding and hydrophobic core interactions prevent denaturing.

  • psychrophile: thrives in extremely low temperatures 4C

    • polaromonas vacuolata

  • mesophile: moderate temperature 39C

    • e.coli, animals, most pathogens

  • thermophile: high temperatures 60C

    • hot spings

  • Hyperthermophiles: extremely hot temperatures

    • deep sea thermal vents

    • saturated lipidsare a characteristic adaptation of hyperthermophiles, allowing their cell membranes to maintain stability and functionality in extreme heat.

Page 4: Environmental Effects on Growth

• pH Effects

  • pH Categories:

    • Neutralophiles: pH 5–8, prevents spontaneous destruction

    • Acidophiles: pH 0–5

    • Alkaliphiles: pH 9–11

  • intracellular pH ALWAYS stays neutral for all

  • Optimal pH Consideration:

    • Refers to extracellular conditions only

    • Intracellular pH must stay close to neutral (pH 5–9) for macromolecule stability

Page 5: Osmolarity and Microbial Growth

• Water Availability

  • Depends on the environmental moisture/dryness and concentration of solutes

  • Water Activity (aw):

    • Ranges from 0 (no free water) to 1 (pure water)

    • Osmolarity is inversely related to water activity

    • Halophiles and Halotolerant Organisms adapt to varying salt concentrations

  • halophiles:

    • thrive in high salt concentrations

  • halotolerant:

    • can tolerate wide range of salt concentrations but dont require them for growth

Page 6: Oxygen Classes of Microorganisms

• Classes of Microorganisms

  • Aerobes: grow in presence O2

    • grow only at the top where O2 is most abundant

  • Microaerophiles: Can use O2 only at reduced levels

    • grow in middle section of tube bc inhibited by high concentrations of O2 at the top

  • Facultative Organisms: Can live with or without oxygen

    • grow throughout the entire tube, but with prominent growth concentrated at the top. This is due to their ability to utilize oxygen for respiration when it is available, but they can also switch to anaerobic metabolism when oxygen levels are low.

  • Aerotolerant Anaerobes: O2 has no impact on growth

    • grow uniformly throughout the medium, as they do not use oxygen for respiration and can metabolize energy anaerobically regardless of the oxygen presence.

  • Obligate Anaerobes: Only grow in the absence of O2

    • grow only at the bottom where O2 is lowest

  • Capacity to detoxify oxygen-derived toxic byproducts

Page 7: Controlling Microbial Growth

• Control Methods

  • Decontamination: Treatment to make objects safe to handle

    • doesn’t eliminate all microbes, only reduce or eliminate pathogens to some level

  • Disinfection: Targets pathogens; does not guarantee killing all microorganisms

    • kills or severely inhibits growth

  • Sterilization: Killing or removal of all living organisms

Page 8: Heat Control Methods

• Heat Treatment Techniques

  • Autoclave:

    • Sealed heating device using steam (moisture) at 121°C to kill endospores (tough structures)

    • Method of sterilization: kills everything

  • Pasteurization:

    • Uses heat to significantly reduce microbial load in heat-sensitive liquids

    • Does not kill all organisms (difference from sterilization)

    • Kills all known pathogenic bacteria

Page 9: Effectiveness of Heat Sterilization

• Figure 4.34: The Autoclave and Moist Heat Sterilization

  • Moist heat is more effective than dry heat at the same temperature

  • water vapor can hydrolyze molecules

Page 10: Radiation and Filtration Control Methods

• Physical Control Methods

  • Ultraviolet Radiation (UV):

    • Wavelength between 220-300 nm affects DNA, leading to cell death

    • Useful for decontaminating surfaces but poor penetration

    • useful for sterilizing medical equipment and water due to its ability to disrupt microbial DNA.

  • Ionizing Radiation:

    • Higher energy and better penetration than UV

    • damages cellular components, leading to the disruption of metabolic processes and eventual cell death.

    • x-rays and gamma rays are examples of ionizing radiation that can penetrate tissues and alter DNA, increasing the risk of mutations and cancer.

    • good for medical supplies, food products, plastic lab ware, etc.

Page 11: Filter Sterilization

• Filtration Techniques

  • Used on heat-sensitive liquids and gases

  • eliminates microbes but dont necessarily kill

  • Pore Size:

    • Pores of filters (0.45 and 0.2 μm) are too small for most living organisms but allow liquids or gases to pass (cells > 0.2 micrometers cannot pass)

Page 12: Chemical Control of Microbial Growth

• Chemical Agents

  • Antimicrobial Agent: Chemical that kills or inhibits growth

    • used internally (drugs, antibiotics)

  • -cidal Agents: Kill microorganisms (e.g., bactericidal, fungicidal)

    • Penicillin: A widely used antibiotic that acts as a bactericidal agent by disrupting the synthesis of the bacterial cell wall

  • -static Agents: Inhibit growth (e.g., bacteriostatic, fungistatic)

Page 13: Antimicrobial Susceptibility Testing

• Figure 4.41: Antimicrobial Agent Susceptibility Assay Using Diffusion Methods

  • Illustrates methods for assessing effectiveness of antimicrobial agents

  • narrow zone = no inhibition

  • wider zone = effective chemical or diffusion of the antimicrobial agent, indicating that it successfully inhibits the growth of the microorganism being tested.