Chapter 7: Fundamentals of Microbial Growth

Microbial Growth and Reproduction

Microbial growth refers to the increase in the number of cells, not cell size. Most bacteria reproduce by binary fission, a process resulting in two identical daughter cells.

• Binary Fission: Asexual process where a single cell divides into two identical cells.

• Generation Time: The time required for a cell to divide and its population to double.

• Growth Curve: Describes the pattern of growth in a closed batch system, typically with four phases.

Four Stages of Bacterial Growth

Physical and Chemical Factors Affecting Microbial Growth

• Temperature: Microbes are classified by their optimal temperature ranges:

  • Psychrophiles: Thrive at 0–20°C (cold-loving).

  • Mesophiles: Grow best at moderate temperatures (20–45°C); most human pathogens.

  • Thermophiles: Prefer 45–70°C (heat-loving).

  • Hyperthermophiles: Grow above 70°C.

• pH: Most bacteria grow best at neutral pH (6.5–7.5). Acidophiles and alkaliphiles thrive in acidic and basic environments, respectively.

• Osmotic Pressure: High salt or sugar concentrations inhibit most microbes (plasmolysis), but halophiles tolerate or require high salt.

• Oxygen Requirements:

  • Obligate aerobes: Require oxygen.

  • Facultative anaerobes: Grow with or without oxygen.

  • Obligate anaerobes: Oxygen is toxic.

  • Microaerophiles: Require low oxygen levels.

  • Aerotolerant anaerobes: Tolerate oxygen but do not use it.

Microbial Control: Sterilization, Disinfection, and Antisepsis

Microbial control methods are used to reduce or eliminate microorganisms from surfaces, equipment, and tissues.

• Sterilization: Complete destruction of all microbial life, including spores.

• Disinfection: Destruction of vegetative pathogens on inanimate objects.

• Antisepsis: Destruction of pathogens on living tissue.

• Sanitization: Lowering microbial counts to safe public health levels.

Methods of Microbial Control

• Physical Methods: Heat (moist and dry), filtration, radiation.

• Chemical Methods: Alcohols, phenolics, halogens, heavy metals, aldehydes, peroxygens.

Levels of Disinfectants

Chapter 8: Microbial Metabolism

Metabolism: Catabolism and Anabolism

Metabolism is the sum of all chemical reactions in a cell. It includes catabolism (breaking down molecules to release energy) and anabolism (building complex molecules from simpler ones).

• Catabolism: Degradative reactions; release energy (exergonic).

• Anabolism: Biosynthetic reactions; require energy (endergonic).

ATP: The Energy Currency

• Structure: Adenosine triphosphate (ATP) contains adenine, ribose, and three phosphate groups.

• Energy Release: Energy is released when ATP is hydrolyzed to ADP + Pi:

• ATP Generation: Substrate-level phosphorylation, oxidative phosphorylation, and photophosphorylation.

Enzymes and Enzyme Regulation

• Enzymes: Biological catalysts that speed up reactions by lowering activation energy.

• Factors Affecting Activity: Temperature, pH, substrate concentration, inhibitors.

• Inhibition:

  • Competitive: Inhibitor binds active site.

  • Noncompetitive: Inhibitor binds allosteric site.

  • Feedback Inhibition: End product inhibits an earlier step in the pathway.

Cellular Respiration and Fermentation

• Glycolysis: Glucose is broken down to pyruvate, producing ATP and NADH.

• Krebs Cycle: Pyruvate is further oxidized, generating CO2, ATP, NADH, and FADH2.

• Electron Transport Chain: NADH and FADH2 donate electrons, generating ATP via oxidative phosphorylation.

• Fermentation: Anaerobic process; regenerates NAD+ and produces organic end products (e.g., lactic acid, ethanol).

Chapter 9: Principles of Infectious Disease and Epidemiology

Pathogens and Disease

• Pathogen: Microorganism capable of causing disease.

• Types of Pathogens:

  • True Pathogen: Causes disease in healthy hosts.

  • Opportunistic Pathogen: Causes disease only under certain conditions (e.g., immunocompromised host).

Classification of Infectious Agents

Stages of Infectious Disease

• Incubation Period: Time between infection and appearance of symptoms.

• Prodromal Period: Early, mild symptoms.

• Acute Period: Disease is most severe.

• Period of Decline: Symptoms subside.

• Convalescent Period: Recovery and return to health.

Transmission of Infectious Diseases

• Direct Contact: Physical interaction (e.g., touching, sexual contact).

• Indirect Contact: Via fomites (inanimate objects), vectors (insects), or airborne droplets.

• Common HAIs (Healthcare-Associated Infections): C. difficile, urinary tract infections, surgical site infections, MRSA.

Chapter 10: Host-Microbe Interactions and Pathogenesis

Normal Microbiota

• Definition: Microorganisms that colonize the body without causing disease; provide protection and aid digestion.

• Differences: Resident microbiota are permanent; transient microbiota are temporary.

Virulence Factors and Pathogenicity

• Virulence Factors: Traits that enhance a pathogen's ability to cause disease (e.g., toxins, capsules, enzymes).

• Pathogenicity: The ability of a microbe to cause disease.

Exotoxins vs. Endotoxins

Immune Evasion Strategies

• Antigenic Variation: Changing surface proteins to evade immune detection.

• Capsule Formation: Prevents phagocytosis.

• Enzyme Production: Destroys host defenses (e.g., IgA protease).

Prevention of Disease Transmission

• Hand washing

• Disinfection of surfaces and equipment

• Isolation of infected patients

• Use of personal protective equipment (PPE)

Additional info: These notes cover core concepts from Chapters 7–10, including microbial growth, metabolism, infectious disease, and host-microbe interactions, with tables and examples for exam preparation.