Microbiology and Food Processing Quiz

Section II Exam Review

• The review covers microbial growth curves, growth requirements, methods of microbial growth control, microbial genetics, viruses and viral life cycles, and parasitic molecules (prions).

Microbial Growth Curve

• Microbial growth follows a typical pattern with distinct phases.
• The phases are lag phase, exponential growth phase, stationary phase, and death phase.
• The graph shows the logarithm (10^x) of viable cells against time (hours).
• The lag phase is a period of adaptation, where cells are adjusting to the new environment.
• The exponential growth phase is a period of rapid cell division.
• The stationary phase is a period where the rate of cell division equals the rate of cell death.
• The death phase is a period of declining cell numbers.

Microbial Growth Requirements

• Microbes need specific conditions to thrive.
• Factors include oxygen requirements, temperature ranges, pH, osmotic pressure, and hydrostatic pressure.
• Oxygen requirements vary—obligate aerobes need oxygen, obligate anaerobes cannot tolerate oxygen, facultative anaerobes can grow with or without it, and aerotolerant anaerobes are unaffected by oxygen.
• Temperature requirements are categorized into psychrophiles (cold-loving), psychrotolerants (tolerate cold), mesophiles (moderate temperatures), thermophiles (heat-loving), and hyperthermophiles (extreme heat).
• Organisms are sensitive to changes in pH.
• Neutrophiles thrive in a narrow range around neutral pH.
• Acidophiles thrive in acidic environments.
• Alkalophiles thrive in alkaline habitats.
• Osmophiles live in high-solute environments.
• Halophiles prefer high salt concentrations.
• Barophiles thrive under high hydrostatic pressure.

Methods of Microbial Growth Control

• Methods to control microbial growth include physical and chemical methods.
• Physical methods include heat (moist and dry), filtration, and radiation.
• Chemical methods include surfactants, disinfectants, and sterilants.
• Terminology related to microbial control includes antisepsis, asepsis, degerming, disinfection, and sterilization.
• The effectiveness of these methods is measured by the zone of inhibition in the Kirby-Bauer test.
• These techniques are key in preventing infections and preserving materials.

Microbial Genetics

• Horizontal gene transfer occurs when genetic material moves between prokaryotic organisms.
• Transformation, transduction, and conjugation are its three main types.
• Transformation involves the uptake of free DNA.
• Transduction involves viruses transferring DNA from one cell to another.
• Conjugation requires direct contact between cells.

Viruses & Viral Life Cycles

• Viruses have capsids, composed of capsomeres, which are crucial structural components.
• Two main capsid types are helical and icosahedral.
• Viruses can be naked or enveloped.
• Viral replication involves specific stages, starting with adsorption (attachment), penetration (entry), uncoating (release of genetic material), synthesis (replication of viral components), assembly (construction of new viruses), and release.

Parasitic Molecules - Prions

• Prions are proteinaceous infectious agents.
• They are made by mammals.
• They have a normal form (cellular PrP) and a disease-causing form (prion PrP).
• Disease-inducing prions affect the structure of PrP by converting its alpha-helical shape to a beta-sheet conformation.
• This change causes problematic deposits in the brain, leading to diseases.