Antimicrobial Chemotherapy – Key Vocabulary

A comprehensive set of vocabulary flashcards covering antimicrobial agents, their mechanisms, resistance, and susceptibility testing concepts from the HCS228 lecture.

Antimicrobial chemotherapy

Treatment of infection with chemical agents that are selectively toxic to microbes.

Selective (differential) toxicity

Property whereby a drug is more harmful to the microorganism than to the human host.

Disinfectant

Toxic chemical used on inanimate surfaces to kill microbes; unsuitable for topical or systemic use.

Antiseptic

Chemical safe for topical application but too toxic for systemic use (e.g., benzalkonium chloride).

Antibiotic

Natural or semisynthetic substance produced by microorganisms that, in dilute solution, inhibits or kills other microbes.

Synthetic drug

Fully laboratory-synthesised antimicrobial molecule (e.g., sulphonamides).

Semi-synthetic antibiotic

Drug created by chemically modifying a natural antibiotic scaffold.

Bactericidal drug

Antibiotic that kills bacteria outright (e.g., β-lactams).

Bacteriostatic drug

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

Narrow-spectrum antibiotic

Antimicrobial active against a limited set of bacterial species.

Broad-spectrum antibiotic

Agent active against a wide variety of Gram-positive and Gram-negative bacteria.

Peptidoglycan (PG)

Mesh-like bacterial cell-wall polymer of NAM-NAG sugars cross-linked by peptide chains.

Transglycosylase

Enzyme that polymerises NAM-NAG units to extend peptidoglycan glycan chains.

Transpeptidase

Enzyme that cross-links peptidoglycan peptides; target of β-lactam antibiotics.

β-lactam antibiotic

Drug class with a four-membered β-lactam ring that inhibits PBPs and blocks cell-wall cross-linking.

Penicillin-binding protein (PBP)

Bacterial enzyme involved in cell-wall synthesis that binds and is inactivated by β-lactams.

Vancomycin

Large glycopeptide antibiotic that binds D-Ala-D-Ala termini of PG precursors in Gram-positives.

Lipid II

Membrane-anchored peptidoglycan precursor targeted by vancomycin.

Polymyxin (Colistin)

Cationic cyclic peptide that disrupts Gram-negative outer membranes by displacing divalent cations from LPS.

Lipopolysaccharide (LPS)

Anionic outer-membrane component of Gram-negatives; binding site for polymyxins.

Rifampicin

RNA polymerase inhibitor that blocks transcription initiation/elongation, used against TB.

RNA polymerase β subunit

Rifampicin binding site within bacterial RNAP responsible for mRNA synthesis.

DNA gyrase

Type II topoisomerase that introduces negative supercoils; inhibited by quinolones.

Quinolone / fluoroquinolone

Synthetic antibiotics (e.g., ciprofloxacin) that inhibit DNA gyrase and block DNA replication.

Aminoglycoside

Amino-sugar antibiotic group (e.g., streptomycin) that binds 16S rRNA of 30S ribosome, causing misreading.

Tetracycline

Broad-spectrum antibiotic that binds 30S A-site, preventing aminoacyl-tRNA entry; usually bacteriostatic.

Macrolide

14-16-membered lactone ring antibiotics (e.g., erythromycin) that block the 50S polypeptide exit tunnel.

Sulphonamide

Synthetic drug that inhibits folate synthesis; often combined with trimethoprim for synergy.

Antimicrobial resistance (AMR)

Ability of microbes to survive antimicrobial doses that would normally inhibit or kill them.

β-lactamase

Enzyme that hydrolyses the β-lactam ring, rendering β-lactam antibiotics inactive.

Horizontal gene transfer (HGT)

Movement of genetic material between bacteria via transformation, transduction or conjugation.

Multi-drug resistance (MDR)

Phenotype in which a microorganism is resistant to multiple classes of antimicrobials.

NDM-1

New Delhi Metallo-β-lactamase-1; plasmid-encoded enzyme conferring resistance to most β-lactams.

Minimum Inhibitory Concentration (MIC)

Lowest concentration of an antibiotic that prevents visible bacterial growth.

Minimum Bactericidal Concentration (MBC)

Lowest concentration of antibiotic that kills 99.9 % of the initial bacterial population.

Breakpoint

Chosen antibiotic concentration or zone size that classifies an isolate as susceptible, intermediate or resistant.

Kirby-Bauer disc diffusion

Agar assay in which antibiotic-impregnated discs create inhibition zones to infer susceptibility.

E-test (gradient strip)

Plastic strip with an antibiotic gradient that produces a direct MIC value on agar.

Broth dilution test

Serial two-fold dilutions of antibiotic in broth used to determine MIC (and MBC with subculture).

Antimicrobial stewardship

Coordinated strategy to optimise antimicrobial use, improve outcomes, and limit resistance.

Conjugation

HGT mechanism where plasmids transfer between bacteria via cell-to-cell contact.

Transformation

Uptake of free DNA from the environment by competent bacteria.

Transduction

Transfer of bacterial DNA mediated by bacteriophages.

Selective pressure

Environmental factor, such as antibiotic exposure, that favours survival of resistant organisms.

Bacteriophage

Virus that infects bacteria; can mediate transduction of resistance genes.

Target-site mutation

Genetic change in an antibiotic’s molecular target that reduces drug binding and confers resistance.

Antibiotic pipeline

Metaphor describing the flow of newly discovered antibiotics, currently in decline since 1987.