Microbiology Exam Review: Antimicrobials, Drug Resistance & Subviral Agents

Vocabulary flashcards covering key concepts in prions, subviral agents, antimicrobial theory, drug testing metrics, resistance mechanisms, and related microbiology terms.

In vivo

Experimental work performed inside a living organism, allowing normal physiological interactions.

In vitro

Experimental work performed outside a living organism, typically in test tubes, petri dishes, or cell culture.

Prion

An infectious misfolded protein that lacks nucleic acid yet induces abnormal folding of normal cellular proteins, leading to neurodegenerative disease.

Examples of prion diseases

Creutzfeldt-Jakob disease (CJD), Bovine Spongiform Encephalopathy (Mad-cow disease), and Scrapie in sheep/goats.

Satellite virus

A subviral agent that requires a helper virus to replicate, e.g., Hepatitis D virus needing Hepatitis B virus.

Viroid

A small, circular, naked RNA molecule that infects plants and lacks a protein coat.

Genome

The complete set of genetic material (DNA or RNA) in an organism or virus.

Gene

A DNA segment that encodes a functional product, usually a protein or RNA molecule.

Genotype

The specific genetic makeup of an organism—the actual nucleotide sequence of its genes.

Phenotype

The observable traits or characteristics of an organism that result from gene expression.

Plasmid

A small, circular, extrachromosomal DNA molecule in bacteria that often carries non-essential but advantageous genes, such as antibiotic resistance.

Ideal antimicrobial characteristics (Table 10.1)

Selective toxicity, microbicidal not microbistatic, remains potent at low dose, soluble and active in tissues/fluids, does not readily lead to resistance, complements host defenses, is reasonably priced, and has no allergic or toxic side effects.

Broad-spectrum drug

An antimicrobial effective against a wide range of microbial types (e.g., both Gram-positive and Gram-negative bacteria).

Narrow-spectrum drug

An antimicrobial effective against a limited group of microbes, often preferred to avoid disrupting normal flora.

Bactericidal

An agent that kills bacteria outright.

Bacteriostatic

An agent that inhibits bacterial growth, relying on host defenses to clear the microbes.

Synergy (drug interaction)

When two drugs administered together produce a greater effect than either alone.

Zone of Inhibition (ZOI)

The clear region around an antimicrobial disk in a Kirby-Bauer assay where bacteria fail to grow; a larger ZOI indicates greater bacterial sensitivity to the drug.

Minimum Inhibitory Concentration (MIC)

The lowest concentration of a drug that visibly prevents microbial growth; a lower MIC signifies higher potency.

Therapeutic Index (TI)

The ratio of a drug’s toxic dose to its effective dose; a higher TI indicates greater safety because a much larger amount would be required to harm the host.

Selective toxicity

The property that allows an antimicrobial to harm the target microbe without damaging host cells.

Five drug categories by mode of action

1) Inhibitors of cell-wall synthesis, 2) Disruptors of cell-membrane structure/function, 3) Inhibitors of nucleic-acid synthesis, 4) Inhibitors of protein synthesis, 5) Inhibitors of essential metabolic pathways (antimetabolites).

Common antibacterial drugs

Penicillins, Cephalosporins, Carbapenems, Tetracyclines, Macrolides, Aminoglycosides, Fluoroquinolones, Sulfonamides.

Common antifungal drugs

Azoles (e.g., Fluconazole), Polyenes (e.g., Amphotericin B, Nystatin), Echinocandins (e.g., Caspofungin).

Common antiprotozoal drugs

Metronidazole, Chloroquine, Artemisinin, Atovaquone-proguanil.

Common antihelminth drugs

Mebendazole, Albendazole, Ivermectin, Praziquantel.

Five major mechanisms of drug resistance

1) Drug-inactivating enzymes (e.g., β-lactamases), 2) Decreased permeability or uptake, 3) Alteration of drug binding sites, 4) Active efflux pumps, 5) Alternative metabolic pathways that bypass the drug-blocked step.

Probiotics

Live microorganisms administered to confer a health benefit by improving or restoring the gut microbiota.

Prebiotics

Non-digestible food components (e.g., inulin, fructooligosaccharides) that selectively stimulate the growth or activity of beneficial gut microbes.

Superinfection

A secondary infection arising when broad-spectrum antibiotics disrupt normal flora, allowing opportunists such as Clostridioides difficile or Candida to overgrow.