Antimicrobial Treatments and Microbial Resistance

Vocabulary flashcards covering antimicrobial chemotherapy principles, modes of action, susceptibility testing, antiparasitic/antiviral agents, resistance mechanisms, and host-microbiome interactions based on the lecture.

Selective toxicity

The primary goal of antimicrobial chemotherapy, defined as destroying an infectious pathogen within a host without causing damage to human tissues.

Antibiotics

Natural secondary metabolites secreted by soil bacteria (such as Streptomyces and Bacillus) and fungi (such as Penicillium and Cephalosporium) to eliminate competing microbes for space and nutrients.

Kirby-Bauer technique

A standardized agar diffusion assay using Muller Hinton agar and drug-impregnated paper discs to determine microbial susceptibility by measuring clear zones of inhibition in millimeters.

Epsilometer test (E-test)

An agar diffusion method utilizing a plastic strip impregnated with a continuous, pre-calibrated exponential gradient of an antimicrobial drug to directly reveal the minimum inhibitory concentration ($MIC$).

Minimum inhibitory concentration (MIC)

The lowest concentration of an antimicrobial drug that visibly prevents bacterial growth.

Tube dilution test

A quantitative assay involving serial dilutions of an antimicrobial in broth-filled tubes or multi-well plates to determine the minimum inhibitory concentration ($MIC$) by observing turbidity.

Therapeutic index (TI)

The ratio of the toxic dose to the minimum effective dose of a drug, quantifying its margin of safety.

Broad-spectrum antimicrobials

Antimicrobial drugs, such as tetracyclines, that target a wide array of pathogens including gram-positive, gram-negative, and intracellular bacteria.

Narrow-spectrum antimicrobials

Antimicrobial drugs, such as polymyxin and natural penicillins, that target specific microbial groups while sparing beneficial commensal microbes.

Bacitracin

A non-beta-lactam antibiotic that interferes with cell wall production at an early transport step rather than directly inhibiting PBPs, primarily used topically on the skin.

Isoniazid

An antibacterial drug that specifically targets the unusual lipid-rich cell wall of mycobacteria, such as Mycobacterium tuberculosis.

Aminoglycosides

Antibiotics, such as streptomycin, that disrupt protein synthesis by targeting the $30\text{S}$ subunit of the bacterial $70\text{S}$ ribosome.

Macrolides

Antibiotics including erythromycin, clarithromycin, and azithromycin that disrupt protein synthesis by inhibiting translocation of the ribosomal subunit during translation.

Antimetabolites

Drugs such as sulfonamides and trimethoprim that block folate metabolism by competitively inhibiting key enzymes required to synthesize tetrahydrofolate.

Fluoroquinolones

Antibiotics such as ciprofloxacin, ofloxacin, and levofloxacin that stop DNA transcription by inhibiting DNA-unwinding enzymes called helicases.

Polymyxins

Antibiotics that distort bacterial cell surface structures and cause leakage of proteins and nitrogen bases, highly effective against gram-negative bacteria like Pseudomonas aeruginosa.

Macrolide polyenes

An antifungal drug class, including amphotericin B, that binds directly to ergosterol to form membrane pores.

Echinocandins

Antifungal drugs that disrupt fungal cell wall construction by inhibiting $\beta\text{-1,3-glucan}$ synthesis without harming host tissue.

Metronidazole

An antiprotozoal drug that is reduced by anaerobic metabolic pathways to form toxic free radicals that damage DNA and essential proteins in organisms like Entamoeba histolytica, Giardia lamblia, and Trichomonas vaginalis.

Albendazole

An antihelminthic drug that inhibits microtubule polymerization in roundworm eggs and larvae to prevent glucose uptake and induce starvation.

Pyrantel

An antihelminthic drug that causes neuromuscular paralysis in intestinal roundworms so hosts can clear them through the GI tract.

Praziquantel

An antihelminthic drug that increases cell membrane permeability to calcium to induce spastic paralysis and integument damage in tapeworms and flukes.

Ivermectin

An antihelminthic drug that hyperpolarizes invertebrate muscle and nerve cells via glutamate-gated chloride channels to treat Strongyloides infections.

Intrinsic resistance

A fixed, inherent adaptive trait of a microbial species, such as self-resistance in antibiotic-producing organisms or outer membrane impermeability in gram-negative bacteria.

Acquired resistance

An adaptive response where a previously sensitive microbe adapts to tolerate a drug through spontaneous chromosomal mutations, horizontal gene transfer, or nonheritable mechanisms.

Persister cells

Non-metabolizing cells commonly found in biofilms that temporarily tolerate antibiotics without undergoing genetic changes.

Host defense peptides

Short chains of $20$ to $50$ amino acids that act as potent antimicrobial agents by disrupting cell membranes and targeting intracellular structures.

CRISPR system

A precise genetic strategy employing RNA-guided Cas9 endonucleases delivered via engineered bacteriophages to target and cut specific resistance genes in pathogens.

Teixobactin

A novel antibiotic discovered using specialized diffusion chambers in soil that inhibits bacterial cell wall synthesis by binding to essential lipid precursors.

Bacteriophage therapy

A revived targeted treatment using host-specific bacterial viruses, such as BioPhage PA, to destroy specific bacterial pathogens like Pseudomonas aeruginosa without harming commensal biota.

Probiotics

Live microbial preparations administered to restore or enhance normal intestinal biota and stimulate host mucosal immunity.

Prebiotics

Nondigestible nutrients, such as complex fructan carbohydrates, that selectively stimulate the growth and metabolic activity of beneficial commensal microbes like Bifidobacterium.

Fecal transplants

The direct introduction of a complete healthy gut ecosystem to restore colonization resistance against recurrent Clostridioides difficile infections and ulcerative colitis.

Superinfection

An overgrowth of opportunistic microbes (such as Candida albicans or Clostridioides difficile) that occurs when broad-spectrum antimicrobials eradicate protective commensal flora.