Antimicrobial Chemotherapy & Resistance – Core Vocabulary

Vocabulary flashcards covering key terms, classes, mechanisms, and resistance concepts from the lecture on antimicrobial chemotherapy and resistance.

Antimicrobial Chemotherapy

Use of drugs to combat infectious agents (bacteria, fungi, parasites, viruses) with differential toxicity toward the pathogen over the host.

Differential Toxicity

Concept that an antimicrobial drug is more toxic to the infecting organism than to the host.

Antibiotic

Substance produced by a microorganism that, in small amounts, inhibits or kills bacteria; may be natural or synthetic.

Penicillin

First antibiotic discovered (1928) from the fungus Penicillium; prototype β-lactam cell-wall inhibitor.

Minimum Inhibitory Concentration (MIC)

Lowest concentration of an antibiotic that inhibits visible growth of a test organism.

Minimum Bactericidal Concentration (MBC)

Lowest concentration of an antibiotic that kills a test organism.

Bacteriostatic

Drug effect that inhibits bacterial growth without necessarily killing cells.

Bactericidal

Drug effect that kills bacteria outright.

Time-Dependent Killing

Antibacterial activity related to the duration the drug concentration remains above the MIC.

Concentration-Dependent Killing

Antibacterial activity related to achieving high peak drug concentrations relative to the MIC.

Prophylaxis (Antimicrobial)

Administration of agents to prevent, rather than treat, infection.

Narrow-Spectrum Antibiotic

Drug active against a limited range of species (e.g., penicillin vs. Gram-positives).

Broad-Spectrum Antibiotic

Drug active against a wide variety of species (e.g., tetracycline vs. Gram-positive and Gram-negative bacteria).

Peptidoglycan

Mesh-like polymer of NAG and NAM sugars cross-linked by peptides; main component of bacterial cell wall.

Penicillin-Binding Proteins (PBPs)

Essential enzymes that catalyze cell-wall synthesis; targets of β-lactam antibiotics.

β-Lactam Antibiotics

Class including penicillins, cephalosporins, cephamycins, carbapenems that inhibit cell-wall synthesis via PBPs.

Glycopeptide Antibiotics

Agents (e.g., vancomycin) that bind D-Ala-D-Ala termini of nascent cell-wall peptides, blocking cross-linking.

Polymyxins

Cationic polypeptide antibiotics (e.g., colistin) that disrupt Gram-negative cell membranes.

Quinolones / Fluoroquinolones

Synthetic drugs that inhibit DNA gyrase and topoisomerase IV, blocking bacterial DNA replication.

Rifamycins

Antibiotic class (e.g., rifampicin) that inhibits bacterial RNA polymerase and DNA-dependent RNA synthesis.

70S Ribosome

Prokaryotic ribosome composed of 50S and 30S subunits; target of many protein-synthesis inhibitors.

Macrolides

50S-binding antibiotics (e.g., erythromycin) that are mainly bacteriostatic against Gram-positives and atypicals.

Lincosamides

50S-binding agents (e.g., clindamycin) active against Gram-positive and anaerobic bacteria.

Aminoglycosides

30S-binding, concentration-dependent bactericidal drugs (e.g., gentamicin) with strong Gram-negative activity.

Tetracyclines

30S-binding, broad-spectrum bacteriostatic antibiotics that block tRNA attachment.

Chloramphenicol

Broad-spectrum antibiotic that binds the 50S subunit and inhibits peptide-bond formation.

Trimethoprim-Sulfamethoxazole (TMP-SMX)

Combination that blocks folic-acid synthesis at two steps, acting synergistically as antimetabolites.

Antimetabolite

Drug that blocks metabolic pathways by mimicking natural substrates (e.g., sulfonamides vs. PABA).

Gram-Positive Bacteria

Organisms with thick peptidoglycan layers retaining crystal-violet stain; lack outer membrane.

Gram-Negative Bacteria

Organisms with thin peptidoglycan plus outer membrane containing lipopolysaccharide; lose crystal violet and stain red.

Outer Membrane

Extra lipid bilayer in Gram-negative bacteria acting as permeability barrier and containing porins.

Lipopolysaccharide (LPS)

Endotoxin molecule in Gram-negative outer membrane contributing to defense and immune activation.

Antiviral Drug

Agent that interferes with one or more stages of viral replication inside host cells.

HAART

Highly Active Antiretroviral Therapy; multi-drug regimen for HIV combining at least three agents from different classes.

Reverse Transcriptase Inhibitors (RTIs)

Antiretrovirals that block viral reverse transcriptase, preventing synthesis of viral DNA from RNA.

Protease Inhibitors (PIs)

Antiretrovirals that inhibit viral protease, blocking maturation of infectious virions.

Fusion Inhibitors

Antiretrovirals (e.g., enfuvirtide) that block entry of virus by preventing fusion with host cell membrane.

Antimicrobial Resistance (AMR)

Ability of microorganisms to survive or grow in presence of antimicrobials previously effective against them.

Inherent (Natural) Resistance

Innate insensitivity of a species to a drug due to lack of uptake, target, or impermeable outer membrane.

Acquired Resistance

Resistance gained via mutation or acquisition of new genes through horizontal or vertical transfer.

Multi-Resistance

Bacterial phenotype resistant to multiple unrelated antibiotic classes (e.g., Pseudomonas aeruginosa).

Cross-Resistance

Resistance to multiple drugs of the same class due to shared mechanism (e.g., all β-lactams).

β-Lactamase

Enzyme that hydrolyzes the β-lactam ring, inactivating β-lactam antibiotics.

Extended-Spectrum β-Lactamase (ESBL)

Plasmid-encoded enzymes that degrade penicillins and cephalosporins, common in Enterobacteriaceae.

Methicillin-Resistant Staphylococcus aureus (MRSA)

S. aureus strain carrying mecA gene encoding PBP2a with low β-lactam affinity.

Vancomycin-Resistant Staphylococcus aureus (VRSA)

S. aureus strains acquiring vanA/vanB genes, altering peptidoglycan to D-Ala-D-Lac and preventing vancomycin binding.

Efflux Pump

Membrane protein that exports antibiotics out of the bacterial cell, lowering intracellular drug concentration.

Target Modification

Resistance mechanism involving structural change of the antibiotic’s binding site (e.g., altered PBPs).

Alternative Pathway (Bypass)

Resistance mechanism where bacteria use a new metabolic route to circumvent drug-blocked step.

Antibiotic Stewardship

Coordinated interventions to optimize antibiotic use, improve outcomes, and reduce resistance.

Overuse of Antibiotics

Inappropriate prescribing, especially for viral infections, accelerating resistance development.

Veterinary Antibiotic Use

Employment of antimicrobials in animals for growth promotion or prophylaxis, contributing to human AMR.

Teixobactin

Novel antibiotic in development with activity against Gram-positive pathogens and low observed resistance.

Priority Pathogens List (WHO)

Global ranking of bacteria where new antibiotics are urgently needed (e.g., carbapenem-resistant A. baumannii).

Alternative Therapies (Antimicrobials)

Non-classical approaches such as phage therapy, antimicrobial peptides, probiotics, or immunotherapy.

Selective Toxicity

Therapeutic goal whereby a drug harms the pathogen with minimal damage to the host.

Porin

Protein channel in Gram-negative outer membrane that allows passive uptake of small molecules, including some antibiotics.

DNA Gyrase

Bacterial enzyme introducing negative supercoils; principal target of quinolones in Gram-negatives.

Topoisomerase IV

Enzyme that decatenates replicated chromosomes; quinolone target mainly in Gram-positives.

70S vs. 80S Ribosomes

Difference between prokaryotic (70S) and eukaryotic (80S) ribosomes enabling selective inhibition of bacterial protein synthesis.

Lipoteichoic Acid

Polymer anchored in Gram-positive cell walls; contributes to cell-wall function and immunogenicity.

Porin Alteration

Resistance mechanism where mutations reduce antibiotic influx through outer-membrane channels.

Carbapenemase

β-lactamase subclass capable of hydrolyzing carbapenem antibiotics, often conferring high-level resistance.

Antibiotic Discovery Gap

Period since the 1980s with few new antibiotic classes reaching the clinic, intensifying the AMR crisis.

Folic Acid Synthesis Inhibitors

Drugs (sulfonamides, trimethoprim) targeting bacterial folate pathway absent in humans, enabling selective toxicity.