Lab 7 – Control of Growth: UV Radiation, Antibiotics, and Conjugation

Vocabulary flashcards covering ultraviolet radiation, DNA damage and repair, antibiotic classes, mechanisms, testing methods, and bacterial conjugation concepts from Lab 7 lecture notes.

Ultraviolet (UV) Radiation

Non-ionizing, short-wavelength (4–400 nm), high-energy radiation used to control microbial growth.

UV-A

The longest-wavelength subdivision of UV light; least damaging to DNA.

UV-B

UV radiation with wavelengths of 280–315 nm; moderately damaging.

UV-C

UV radiation of 100–280 nm; most damaging, especially around 254–260 nm.

Pyrimidine Dimer

Covalent linkage of adjacent thymine or cytosine bases in DNA caused by UV exposure.

Thymine-Thymine Dimer

Most common pyrimidine dimer; kinks DNA and blocks polymerase activity.

SOS Repair System

Bacterial emergency pathway that excises UV-induced dimers and replaces them with new pyrimidines.

Endospore UV Resistance

Protection afforded by acid-soluble proteins and repair enzymes within bacterial spores.

Biofilm UV Protection

Physical shielding provided by multicellular bacterial communities that reduces UV penetration.

Natural Antibiotic

Antimicrobial metabolite produced by bacteria or fungi to inhibit nearby competitors.

Semi-Synthetic Antibiotic

Drug whose core active moiety is natural but whose side chain (R-group) is chemically modified (e.g., ampicillin).

Synthetic Antibiotic

Completely laboratory-made antimicrobial, such as sulfonamides.

Beta-Lactam Moiety

Four-membered ring common to penicillins and related antibiotics; inhibits cell-wall synthesis.

Bactericidal Antibiotic

Drug that kills bacteria outright.

Bacteriostatic Antibiotic

Drug that halts bacterial growth, relying on host immunity to clear infection.

Narrow-Spectrum Antibiotic

Agent effective against a limited group (usually one Gram category) of bacteria.

Broad-Spectrum Antibiotic

Agent effective against both Gram-positive and Gram-negative bacteria; risks disrupting normal microbiota.

Selective Toxicity

Property of targeting microbes without harming host cells; high for penicillin, low for polymyxin B.

Penicillin

First commercial antibiotic; natural beta-lactam that blocks peptidoglycan cross-linking.

Ampicillin

Semi-synthetic penicillin derivative with a broader spectrum than penicillin G.

Sulfonamide

Synthetic antibiotic class that inhibits folic-acid synthesis in bacteria.

Cell-Wall Synthesis Inhibitors

Antibiotics like penicillin that block peptidoglycan formation.

Protein Synthesis Inhibitors

Agents such as tetracycline that target bacterial ribosomes.

Membrane Disruptors

Antibiotics like polymyxin B that compromise bacterial cell membranes.

DNA/RNA Synthesis Inhibitors

Drugs such as ciprofloxacin (DNA gyrase) or rifampicin (RNA polymerase) that stop nucleic-acid replication or transcription.

Kirby-Bauer Method

Standardized disk-diffusion assay on Mueller-Hinton agar for qualitative antibiotic sensitivity testing.

Zone of Inhibition

Clear area around an antibiotic disk where bacterial growth is prevented; measured in millimeters.

E-Test

Strip diffusion method that provides a gradient of antibiotic concentrations to determine MIC quantitatively.

Minimum Inhibitory Concentration (MIC)

Lowest antibiotic concentration that visibly inhibits bacterial growth in vitro.

Horizontal Gene Transfer

Movement of genetic material between unrelated cells (conjugation, transformation, transduction, transposons).

Conjugation

Direct plasmid transfer from donor to recipient bacterium via a sex pilus, producing recombinants.

Transformation

Uptake of free DNA from the environment by competent bacteria.

Transduction

DNA transfer between bacteria mediated by bacteriophages.

Plasmid

Small, circular, double-stranded DNA molecule carrying non-essential genes such as antibiotic resistance.

Sex Pilus

Surface appendage used by donor bacteria to initiate plasmid transfer during conjugation.

Recombinant Cell

Recipient bacterium that has acquired and incorporated foreign genetic material.

Streptomycin Resistance Gene (strᵣ)

Chromosomal determinant in E. coli Strain I that confers streptomycin resistance.

Ampicillin Resistance Gene (ampᵣ)

Plasmid-borne determinant in E. coli Strain II that confers ampicillin resistance.

What is the process of this picture shown

bacterial conjugation

This results in a recombinant cell.

•Biofilms bring bacteria closer together making it easier to transfer genes.