Comprehensive Study Guide: Recombinant DNA Technology, Microbial Control, Antimicrobial Drugs, Prokaryote Classification, Eukaryotes, Viruses, and Epidemiology

Recombinant DNA Technology and Biotechnology

Definitions and Key Concepts

• Biotechnology: The use of living organisms or their products to modify human health and the human environment.

• Recombinant DNA Technology: Techniques for combining genes from different sources into a single DNA molecule, often involving the insertion of foreign genes into organisms to produce desired products.

• Key Differences: Biotechnology is the broader field; recombinant DNA technology is a subset focused on genetic manipulation.

Examples and Applications

• Production of insulin, human growth hormone, vaccines, and genetically modified crops.

• Creation of transgenic organisms for agriculture and medicine.

Main Goals of Recombinant DNA Technology

• Eliminate undesirable phenotypic traits.

• Combine beneficial traits of two or more organisms.

• Create organisms that synthesize products humans need.

Tools of Recombinant DNA Technology

• Mutagens: Chemicals or physical agents that create mutations.

• Reverse Transcriptase: Enzyme that synthesizes cDNA from RNA.

• Restriction Enzymes: Cut DNA at specific sequences.

• Vectors: DNA molecules (e.g., plasmids, viruses) used to deliver genetic material into cells.

Polymerase Chain Reaction (PCR)

• Purpose: Amplifies specific DNA sequences.

• Steps: Denaturation (separates DNA strands), Priming (binds primers), Extension (synthesizes new DNA).

• Equation for DNA molecules after n cycles: $2^n$

• Importance of Thermus aquaticus: Its DNA polymerase is heat-stable, enabling PCR automation.

Gel Electrophoresis

• Separates DNA fragments by size using an electric field.

• Smaller fragments move faster through the gel matrix.

DNA Insertion Methods

• Natural Methods: Transformation, transduction, conjugation.

• Artificial Methods: Electroporation, protoplast fusion, microinjection, gene gun.

Genomics and Sequencing

• Genomics: Study of an organism's entire genome.

• Transcriptomics: Study of RNA transcripts.

• Metabolomics: Study of metabolic products.

• Functional Genomics: Study of gene functions and interactions.

• Sanger Sequencing: Chain-termination method; Next-Generation Sequencing: Massively parallel sequencing, faster and cheaper.

Applications and Ethics

• Medical: Gene therapy, vaccine production, diagnostic tests.

• Agricultural: Pest-resistant crops, improved yields.

• Ethics: Concerns about safety, environmental impact, and genetic privacy.

Controlling Microbial Growth in the Environment

Definitions and Methods

• Sterilization: Destruction of all microbes, including endospores and viruses.

• Disinfection: Destruction of most microbes on nonliving surfaces.

• Antisepsis: Reduction of microbes on living tissue.

• Degerming: Removal of microbes by mechanical means (e.g., handwashing).

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

• Pasteurization: Use of mild heat to reduce microbes in food and beverages.

Microbial Death Rate

• Describes the rate at which microbes are killed.

• Often follows a logarithmic decline.

• Equation: $N_t = N_0 \times 10^{-kt}$, where $N_t$ is the number of survivors at time $t$, $N_0$ is the initial number, and $k$ is the death rate constant.

Physical Methods of Control

• Heat (moist and dry), refrigeration, freezing, desiccation, lyophilization, filtration, osmotic pressure, radiation.

• Autoclave: Uses moist heat under pressure for sterilization.

• Dry Heat: Used for materials that cannot be sterilized by moist heat.

Chemical Methods of Control

• Phenolics, alcohols, halogens, oxidizing agents, surfactants, heavy metals, aldehydes, gaseous agents, enzymes.

• Each has specific mechanisms, advantages, and disadvantages.

Levels of Microbial Resistance

Group	Resistance Level	Examples
Bacterial Endospores	Highest	Bacillus, Clostridium
Mycobacteria	High	Mycobacterium tuberculosis
Cysts of Protozoa	High	Giardia

Biosafety Levels

• BSL-1: Non-pathogenic microbes.

• BSL-2: Moderate risk; gloves, lab coats.

• BSL-3: Aerosol transmission; biosafety cabinets.

• BSL-4: Dangerous/exotic agents; pressurized suits.

Antimicrobial Drugs

History and Principles

• Key contributors: Paul Ehrlich (chemotherapy), Alexander Fleming (penicillin), Selman Waksman (streptomycin), Gerhard Domagk (sulfa drugs).

• Selective Toxicity: Drugs target microbial structures/functions not found in host.

Mechanisms of Action

• Inhibition of cell wall synthesis (e.g., penicillins, cephalosporins).

• Inhibition of protein synthesis (e.g., tetracyclines, aminoglycosides).

• Disruption of cytoplasmic membrane (e.g., polymyxins, amphotericin B).

• Inhibition of nucleic acid synthesis (e.g., quinolones, rifampin).

• Inhibition of metabolic pathways (e.g., sulfonamides).

• Inhibition of pathogen attachment/entry (e.g., attachment antagonists).

Drug Resistance

• Mechanisms: Enzyme destruction, altered targets, decreased uptake, efflux pumps, biofilm formation, metabolic pathway changes, target overproduction.

• R Plasmids: Carry resistance genes; spread by conjugation.

• Cross Resistance: Resistance to multiple drugs with similar mechanisms.

• Multiple Resistance: Resistance to drugs with different mechanisms.

Testing and Administration

• Diffusion susceptibility (Kirby-Bauer), Etest, MIC, MBC tests.

• Routes: Oral, intramuscular, intravenous.

• Therapeutic Index: $\text{TI} = \frac{\text{Toxic Dose}}{\text{Therapeutic Dose}}$

Characterizing and Classifying Prokaryotes

Prokaryotic Morphology and Reproduction

• Shapes: Coccus, bacillus, coccobacillus, vibrio, spirillum, spirochete, pleomorphic, star-shaped, filamentous.

• Arrangements: Singles, pairs, chains, clusters, tetrads, sarcinae, palisades.

• Reproduction: Binary fission, snapping division, budding.

• Endospores: Dormant, highly resistant structures formed by some bacteria (e.g., Bacillus, Clostridium).

Taxonomy and Classification

• Bergey’s Manual: Standard reference for bacterial classification.

• Domains: Bacteria, Archaea.

• Archaea: Extremophiles (thermophiles, halophiles), methanogens.

Proteobacteria

• Six classes: Alpha-, Beta-, Gamma-, Delta-, Epsilon-, Zeta-proteobacteria.

• Key genera: Rickettsia, Brucella, Neisseria, Pseudomonas, Escherichia.

Characterizing and Classifying Eukaryotes

Eukaryotic Reproduction

• More complex than prokaryotes: Mitosis, meiosis, cytokinesis, schizogony.

• Haploid vs. diploid: One vs. two sets of chromosomes.

Protozoa

• Unicellular, lack cell walls, motile at some stage.

• Reproduction: Asexual (binary fission, budding, schizogony), sexual (conjugation).

• Groups: Euglenozoa, Alveolates, Amoebozoa, Parabasalids, Diplomonads, Rhizaria.

Fungi

• Cell walls of chitin, heterotrophic, absorb nutrients.

• Body shapes: Yeasts (unicellular), molds (filamentous), dimorphic.

• Reproduction: Asexual (spores), sexual (spores).

Algae and Water Molds

• Algae: Photosynthetic, aquatic, diverse cell walls.

• Water molds: Oomycetes, differ from true fungi in cell wall composition and life cycle.

Parasitic Worms and Arthropod Vectors

• Helminths: Studied due to their role as human pathogens.

• Arthropods: Insects and arachnids can transmit diseases (vectors).

Characterizing and Classifying Viruses, Viroids, and Prions

Viruses

• Virus: Acellular, obligate intracellular parasite.

• Virion: Complete infectious viral particle.

• Genome: dsDNA, ssDNA, dsRNA, ssRNA; linear or circular; segmented or non-segmented.

• Capsid shapes: Helical, polyhedral, complex.

• Enveloped vs. non-enveloped viruses.

Viral Replication

• Lytic cycle: Attachment, entry, synthesis, assembly, release.

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

• Animal virus replication: Entry by direct penetration, membrane fusion, or endocytosis.

Viroids and Prions

• Viroids: Small, circular ssRNA molecules, infect plants, do not code for proteins.

• Prions: Infectious proteins, cause neurodegenerative diseases (e.g., Creutzfeldt-Jakob disease).

Infection, Infectious Diseases, and Epidemiology

Symbiosis and Microbiota

• Types: Mutualism, commensalism, amensalism, parasitism.

• Microbiome: Resident and transient microbiota.

Pathogenesis

• Reservoirs: Human, animal (zoonoses), nonliving.

• Portals of entry: Skin, mucous membranes, placenta, parenteral route.

• Adhesion factors: Fimbriae, glycocalyces, biofilms.

• Virulence factors: Enzymes, toxins, antiphagocytic factors.

Stages of Infectious Disease

• Incubation, prodromal, illness, decline, convalescence.

Transmission

• Contact: Direct, indirect, droplet.

• Vehicle: Airborne, waterborne, foodborne.

• Vector: Biological, mechanical.

Epidemiology

• Incidence vs. prevalence.

• Endemic, sporadic, epidemic, pandemic.

• Healthcare-associated infections (HAIs): Exogenous, endogenous, iatrogenic, superinfections.

Public Health

• Surveillance, reporting, and control of infectious diseases.