Microbial Control, Growth, and Genetics: Comprehensive Study Notes

Microbial Control and Antimicrobial Actions

Six Actions of Antibiotic Microbial Control

Antibiotics and antimicrobial agents control microbial growth by targeting specific cellular structures and processes:

• Inhibit protein synthesis: Target 70S ribosomes, preventing translation of proteins.

• Inhibit metabolic pathways: Block essential enzymes, disrupting cellular metabolism.

• Disrupt cytoplasmic membrane: Damage phospholipid bilayer, causing cell lysis.

• Inhibit nucleic acid synthesis: Prevent DNA replication and RNA transcription.

• Cell wall inhibitor: Block cross-linking of NAM subunits, weakening cell wall.

• Inhibit attachment: Prevent formation of extracellular matrix (ECM) and block protein receptors.

Definitions: Cidal, Static, Sanitation, Sterilization, Pasteurization

• Cidal: Refers to agents that kill microorganisms.

• Static: Refers to agents that inhibit microbial growth without killing.

• Sanitation: Reduction of microbial organisms to safe public health levels.

• Sterilization: Complete removal or killing of all microorganisms, including spores.

• Pasteurization: Heat process that kills most pathogens while preserving other cellular structures. Methods include:

  • Low-temperature long-time (LTLT)

  • High-temperature short-time (HTST)

  • Ultra-high-temperature (UHT)

Definitions: Antiseptic, Disinfectant, Antibiotic, Ultraviolet Light, Heat/Freezing, Psychro, Meso, Thermo

• Antiseptic: Chemical agent used on skin/mucous membranes to destroy or inhibit microorganisms.

• Disinfectant: Chemical agent used on inanimate objects to destroy microorganisms (few kill spores).

• Antibiotic: Natural products from fungi/bacteria that inhibit growth of other microorganisms.

• Ultraviolet light: Nonpenetrating, nonionizing radiation (1-400 nm) causing thymine dimers in DNA.

• Heat/Freezing: Heat denatures proteins; freezing halts metabolic activity.

• Psychro: Cold-loving organisms (-5°C to 20°C).

• Meso: Moderate temperature organisms (20°C to 50°C).

• Thermo: Heat-loving organisms (50°C to 80°C).

Autoclave, Biosafety Levels, Obligate, Facultative

• Autoclave: Device that kills all microorganisms by using pressurized steam.

• Obligate: Organisms with limited environmental range.

• Facultative: Organisms with broad environmental range.

• Biosafety Levels (BSL): Classification of laboratory safety based on pathogen risk:

  • BSL-1: Non-disease-causing in healthy humans.

  • BSL-2: Moderately hazardous, easily controlled (e.g., Salmonella, Staphylococcus aureus, MRSA, influenza).

  • BSL-3: Severe disease if inhaled (e.g., SARS-CoV-2, TB, yellow fever, anthrax).

  • BSL-4: Always severe/fatal disease (e.g., Ebola, smallpox).

Moist Heat vs Dry Heat

• Moist heat: More effective for disinfecting, sterilizing, and pasteurizing.

• Dry heat: Used for sterilizing powders, glassware, metal; less effective.

Structures Targeted by Heat

• Proteins, enzymes, and DNA are denatured or damaged by heat.

Mechanism of Autoclaving

• Increased pressure raises boiling point of water, allowing steam to reach >100°C.

• Standard autoclave operates at 15 psi to achieve sterilization.

Filtration and Filter Sizes

• Filtration: Sterilizes by passing liquids/gases through membranes with specific pore sizes.

• Virus filtration: Requires pores of 0.1 nm or smaller.

Osmosis and Solution Types

• Osmosis: Water moves across membrane from high to low concentration.

• Hypertonic: Higher solute outside; cell shrinks (plasmolysis).

• Hypotonic: Lower solute outside; cell swells.

• Isotonic: Equal solute concentration.

Oxidizing Agents and Halogens

• Oxidizing agents: Rip electrons from cellular components via redox reactions (e.g., iodine, hydrogen peroxide).

• Halogens: Damage cellular components, disrupt vital processes (e.g., chlorine, iodine).

• All halogens are oxidizing agents, but not all oxidizing agents are halogens.

Surfactants and QUATS

• Surfactants: Reduce surface tension, aiding in cleaning and microbial removal.

• QUATS (Quaternary Ammonium Compounds): Act as surfactants and disinfectants; Pseudomonas aeruginosa can grow in them.

Heavy Metals and Gaseous Agents

• Heavy metals: Denature proteins and damage DNA (e.g., silver sulfadiazine, silver nitrate, copper sulfate).

• Gaseous agents: Sterilize by alkylation; used for heat/moisture-sensitive materials.

Lysozymes and Prionzymes

• Lysozymes: Enzymes found in tears, saliva, mucus, sweat; break down peptidoglycan in bacterial cell walls.

• Prionzyme: Enzyme developed to degrade prions.

Contributions of Key Scientists

• Ehrlich: Magic bullet concept, syphilis treatment.

• Fleming: Discovered penicillin.

• Florey & Chain: Developed penicillin for medical use.

• Domagk: Developed sulfa drugs (Prontosil).

• Waksman & Schatz: Streptomycin for TB; coined 'antibiotic'.

Microbial Metabolism and Nutrition

Definitions: Chemotherapy, Antibiotic, Semisynthetic & Synthetic Antimicrobials, Selective Toxicity, Generation Time

• Chemotherapy: Use of chemicals to destroy infectious agents without harming the host.

• Semisynthetic: Antibiotics chemically modified in the lab.

• Synthetic drugs: Fully synthesized chemical agents.

• Selective toxicity: Agent is more harmful to pathogen than host.

• Generation time: Time required for microbial population to double.

Microbial Nutrition Types

• Chemoheterotroph: Energy from chemicals, carbon from organic compounds (most bacteria, animals).

• Chemoautotroph: Energy from inorganic chemicals, carbon from CO2.

• Photoheterotroph: Energy from light, carbon from organic compounds.

• Photoautotroph: Energy from light, carbon from CO2 (plants, algae, cyanobacteria).

Examples of Antibiotics by Method

• Inhibit protein synthesis: Tetracycline, Chloramphenicol

• Inhibit metabolic pathways: Sulfamethoxazole/Trimethoprim (SxT)

• Disrupt cytoplasm: Polymyxin B

• Inhibit nucleic acid synthesis: Nalidixic acid

• Cell wall inhibitor: Penicillin, Vancomycin

Spectrum of Antimicrobial Drugs

• Broad-spectrum: Effective against many organisms.

• Narrow-spectrum: Effective against few organisms.

Routes of Administration

• Topical: External infections.

• Oral: Self-administered, no needles.

• Intramuscular: Injection into muscle.

• Intravenous: Directly into vascular system.

Synergism and Resistance

• Synergism: Combined effect of two antimicrobials is greater than sum of individual effects.

• Slowing resistance: Limit antibiotic use, promote vaccination, educate on completing antibiotics.

• Superbugs: Pathogens resistant to common medications (e.g., MRSA).

• Multi-drug resistance: Resistance to three or more antibiotics.

Microbial Genetics and Growth

Genetic Exchange Mechanisms

• Transformation: Uptake of DNA from environment.

• Transduction: Transfer of bacterial DNA by viruses.

• Conjugation: Direct transfer of genetic material between bacteria.

Cidal vs Static Modes of Action

• Cidal: Disrupts cell wall, membrane, inhibits nucleic acid synthesis.

• Static: Inhibits metabolic pathways.

• Either: Inhibits protein synthesis.

Probiotics and R-Plasmids

• Probiotics: Live normal flora (bacteria/yeasts) providing health benefits when consumed.

• R-plasmids: Small, circular DNA molecules conferring antibiotic resistance; transferred during conjugation.

Bacterial Growth Curve

The bacterial growth curve illustrates the population dynamics of bacteria over time in a closed system. It consists of four main phases:

• Lag phase: Cells adapt to environment; no significant increase in number.

• Exponential (log) phase: Rapid cell division; population doubles at regular intervals.

• Stationary phase: Growth rate slows; nutrients deplete, waste accumulates; cell division equals cell death.

• Death phase: Cell death exceeds cell division; population declines.

Oxygen Requirements of Microorganisms

• Aerobe: Requires oxygen for growth.

• Anaerobe: Cannot survive in oxygen.

• Facultative anaerobe: Can use oxygen if present, but can switch to fermentation.

Nitrogen Fixation

• Bacteria: Rhizobium and cyanobacteria perform nitrogen fixation.

• Importance: Converts atmospheric N2 to usable forms for organisms.

Phosphorus and Sulfur

• Phosphorus: Essential for phospholipid membranes, DNA, RNA, ATP, and some proteins.

• Sulfur: Component of sulfur-containing amino acids, disulfide bonds, and some vitamins.

Trace Elements and Growth Factors

• Trace elements: Required in small amounts (e.g., zinc, iron).

• Growth factors: Organic chemicals not synthesized by certain organisms (e.g., vitamins, amino acids, purines, pyrimidines, cholesterol, NADH, heme).

Biofilms and Microbiomes

Biofilm Protection and Communication

• Protection: Extracellular matrix and glycocalyx shield biofilms from environmental threats.

• Communication: Quorum sensing enables coordinated behavior among biofilm cells.

Biofilm Growth and Examples

• Growth surfaces: Environmental surfaces, implanted medical devices, mucous membranes.

• Helpful examples: Sewage plants, septic tanks.

• Biofilm-associated infections: Common in medical devices and oral cavity.

Human Microbiome Project

• Research initiative to characterize microbial communities in the human body and their roles in health and disease.

Halophiles

• Microorganisms that thrive in high-salt environments.