Chapter 6: Microbe Nutrition and Growth

Macronutrients vs. Trace Elements

Microorganisms require various nutrients for growth, which are classified based on their quantity and function.

• Macronutrients: Essential elements needed in large amounts. Examples: Carbon (C), Nitrogen (N), Oxygen (O), Hydrogen (H), Phosphorus (P), Sulfur (S).

• Trace Elements: Required in small amounts, often as cofactors for enzymes. Examples: Iron (Fe), Zinc (Zn), Copper (Cu), Manganese (Mn).

Types of Microbial Nutrition

Microbes are classified based on their energy and carbon sources.

• Photoautotrophs: Use light as energy and CO2 as carbon source. Example: Cyanobacteria.

• Photoheterotrophs: Use light for energy but organic compounds for carbon. Example: Rhodobacter.

• Chemoautotrophs: Use inorganic chemicals for energy and CO2 for carbon. Example: Nitrosomonas.

• Chemoheterotrophs: Use organic compounds for both energy and carbon. Example: Most bacteria, fungi, protozoa.

Transport Mechanisms

Microbes transport nutrients across membranes by passive or active methods.

• Passive Transport: Movement down concentration gradient, no energy required. Includes diffusion and facilitated diffusion.

• Active Transport: Movement against concentration gradient, requires energy (ATP).

Effects of Osmotic Conditions

Cells respond differently to various osmotic environments.

• Isotonic: No net movement of water; cell remains stable.

• Hypotonic: Water enters cell; may cause lysis.

• Hypertonic: Water leaves cell; cell shrinks (plasmolysis).

Biofilms

Biofilms are complex communities of microbes attached to surfaces, embedded in a self-produced matrix.

• Provide protection from environmental stress and antibiotics.

• Common in medical devices and natural environments.

Microbial Growth: Generation Time and Binary Fission

Microbial growth involves cell division, typically by binary fission.

• Generation Time: Time required for a cell to divide.

• Binary Fission: Process by which bacteria reproduce, resulting in two identical cells.

Growth Curve Phases:

• Lag Phase: Adaptation, no increase in cell number.

• Log (Exponential) Phase: Rapid cell division.

• Stationary Phase: Growth rate slows, nutrients deplete.

• Death Phase: Cells die due to lack of nutrients and accumulation of waste.

Requirements and Terminology for Growth

• Physical: Temperature, pH, osmotic pressure.

• Chemical: Nutrients, oxygen, water.

• Terminology: Obligate aerobes, facultative anaerobes, obligate anaerobes, microaerophiles.

Measuring Microbial Growth

• Direct Methods: Plate counts, microscopic counts.

• Indirect Methods: Turbidity, metabolic activity.

Types of Culture Media

• Physical States: Liquid (broth), solid (agar), semi-solid.

• Selective Media: Suppresses unwanted microbes, encourages desired ones. Example: MacConkey agar.

• Differential Media: Distinguishes between organisms. Example: Blood agar.

• Enriched Media: Contains extra nutrients for fastidious organisms. Example: Chocolate agar.

• Defined Media: Exact chemical composition known.

• Complex Media: Contains extracts, composition varies.

Chapter 7: Physical and Chemical Control of Microbes

Definitions: Sterilization, Disinfection, Antisepsis

• Sterilization: Destruction of all microbial life, including spores.

• Disinfection: Removal of pathogens from surfaces.

• Antisepsis: Removal of pathogens from living tissue.

Factors Affecting Elimination of Bacteria

• Number of microbes

• Environment (organic matter, temperature, biofilms)

• Time of exposure

• Microbial characteristics

Microbial Resistance to Control Measures

Types of Control

• Physical: Heat, filtration, radiation.

• Chemical: Disinfectants, antiseptics.

• Mechanical: Scrubbing, washing.

Physical Methods

• Heat: Denatures proteins. Includes moist heat (autoclaving), dry heat (incineration).

• Filtration: Removes microbes from liquids or air.

• Radiation: Damages DNA. Includes UV, ionizing radiation.

Chemical Methods

• Bacteriostatic: Inhibits growth.

• Bactericidal: Kills bacteria.

• MIC (Minimum Inhibitory Concentration): Lowest concentration of drug that prevents growth.

• Zone of Inhibition: Area around an antimicrobial disk where bacteria do not grow.

• Sterilant: Chemical that sterilizes.

• Disinfectant: Used on surfaces.

• Sanitizer: Reduces microbial numbers.

• Antiseptic: Used on living tissue.

Examples of Chemical Agents

• Phenol, Phenolics: Disrupt plasma membrane.

• Iodine (Tinctures): Alters protein synthesis.

• Chlorine (Bleach): Oxidizing agent.

• Heavy Metals: Denature proteins.

• Alcohols (Ethanol): Denature proteins.

• Organic Acids: Control molds/bacteria in foods and cosmetics.

• Gaseous Sterilants: Used for heat-sensitive materials. Example: Ethylene oxide.

Desirable Characteristics of Chemical Control Agents

• Broad-spectrum activity

• Non-toxic to humans

• Stable

• Cost-effective

Chapter 20: Antimicrobial Drugs

History and Selective Toxicity

• Alexander Fleming: Discovered penicillin.

• Selective Toxicity: Drug kills microbes without harming host.

• Broad Spectrum: Effective against many microbes.

• Narrow Spectrum: Effective against specific microbes.

Cell Wall Synthesis Inhibitors

• Penicillin: Beta-lactam antibiotic; inhibits cell wall synthesis.

Testing Antimicrobial Activity

• Disk Diffusion: Measures zone of inhibition.

• Broth Dilution: Determines MIC.

Antimicrobial Drug Resistance

• Microbes develop mechanisms to evade drugs.

• Can be due to mutations or acquisition of resistance genes.

Chapter 8: Microbe Genetics

DNA Structure

• Double helix composed of nucleotides (A, T, G, C).

• Base pairing: A-T, G-C.

Replication

• DNA polymerase synthesizes new DNA strands.

• Replication fork: Site where DNA is unwound.

• Leading strand: Synthesized continuously.

• Lagging strand: Synthesized in fragments (Okazaki fragments).

Equation:

Gene Expression

• Transcription: DNA to RNA, catalyzed by RNA polymerase.

• Translation: RNA to protein.

Equation:

Recombination

• Exchange of genetic material between DNA molecules.

Horizontal Gene Transfer

• Transformation: Uptake of naked DNA.

• Transduction: Transfer via bacteriophage. Generalized: Any gene; Specialized: Specific genes.

• Conjugation: DNA transfer via direct contact; involves F plasmids. Hfr: High frequency recombination.

Mutations

• Auxotroph: Mutant requiring additional nutrients.

• Induced Mutations: Caused by external agents.

• Spontaneous Mutations: Occur naturally.

• Ames Test: Detects mutagenic potential of chemicals.

Chapter 12: Eukaryotes

Fungi

• Characteristics: Eukaryotic, cell wall of chitin, heterotrophic.

• Beneficial effects: Antibiotic production (e.g., penicillin), decomposition.

• Harmful effects: Cause diseases (mycoses), spoil food.

• Lichens: Symbiotic association of fungus and alga; fungus provides structure, alga provides photosynthesis.

Algae

• Characteristics: Eukaryotic, photosynthetic, cell wall of cellulose.

• Beneficial effects: Oxygen production, food source.

• Harmful effects: Toxins (red tides), water blooms.

• Differences: Algae are photosynthetic, bacteria lack nucleus, fungi are heterotrophic.

Protozoa

• Characteristics: Unicellular, eukaryotic, lack cell wall.

• Examples: Amoeba, Paramecium.

Parasitic Helminths

• Characteristics: Multicellular, eukaryotic, parasitic.

• Examples: Ascaris, Taenia.

Chapter 13: Viruses

Structure of Viruses

• Capsid: Protein coat.

• Capsomeres: Subunits of capsid.

• Nucleocapsid: Capsid plus nucleic acid.

• Shapes: Spherical, rod, complex.

• Enveloped vs. Naked viruses: Enveloped have lipid membrane; naked lack envelope.

• Viral surface proteins (spikes): Important for attachment.

Virus Cultivation

• Methods: Cell cultures, embryonated eggs, animals.

Plaques and Replication Cycles

• Plaques: Clear zones on cell layers due to viral lysis.

• Lytic Cycle: Virus replicates and lyses host cell.

• Lysogenic Cycle: Viral DNA integrates into host genome (prophage).

Retroviruses

• Contain RNA genome, reverse transcriptase.

Effects on Animal Cells

• Cytopathic Effects (CPE): Structural changes in host cells due to viral infection.

Viroids and Prions

• Viroids: Infectious RNA molecules, affect plants.

• Prions: Infectious proteins, cause neurodegenerative diseases.