Microbiology Lecture 33: Antimicrobials and Chemotherapy

Flashcards covering the definitions, history, and mechanisms of action for antimicrobial and chemotherapy agents, with a focus on cell wall inhibitors and beta-lactam antibiotics.

Ethylene oxide (EtO)

An antimicrobial gas used for sterilization that destroys proteins by alkylation; it is microbicidal, sporicidal, penetrates plastic wraps, but is highly explosive.

Chemotherapeutic agent

Any chemical agent used in medical practice.

Antimicrobial

An umbrella term for any substance that kills or inhibits microorganisms, including bacteria, fungi, viruses, and parasites; can be natural or synthetic.

Antibiotic

A subset of antimicrobials traditionally produced by microorganisms (though now often modified or synthetic) used mainly against bacteria.

Compound 606

Also known as Salvarsan, it was discovered by Paul Ehrlich and Sahachiro Hata in the early 1900s to kill Treponema pallidum.

Penicillin

The first natural antibiotic, discovered by Alexander Fleming in 1928 from Penicillium mold; its structure was later resolved by Dorothy Hodgkin in the 1940s.

Prontosil

The first synthetic antimicrobial, identified as Sulfanilamide, discovered in the 1930s by Gerhard, Josef, and Fritz.

Streptomycin

Discovered by Selman Waksman from soil microbes, it became the first effective treatment for tuberculosis.

Selective toxicity

The ability of a drug to harm microbes without damaging the host, often by disturbing enzymes or structures unique to the target cell.

Chemotherapeutic Index

A measure of a drug’s safety margin, calculated by looking at the difference between the maximum tolerable dose and the minimum curative dose.

Maximum tolerable dose

The highest dose per kilogram of body weight that the host can tolerate without toxic effects.

Minimum curative dose

The lowest dose per kilogram of body weight required to cure a disease.

Narrow spectrum

Antimicrobials that target only specific subsets of bacterial pathogens.

Broad spectrum

Antimicrobials that target a wide variety of bacterial pathogens, including both Gram-positive and Gram-negative species.

Bacteriostatic agents

Drugs that inhibit bacterial multiplication but do not directly kill the bacteria, such as Tetracycline which blocks protein synthesis.

Bactericidal agents

Drugs that kill bacteria without necessarily causing immediate cell lysis, such as Fluoroquinolones which damage bacterial DNA.

Bacteriolytic agents

Drugs that kill bacteria by causing cell lysis through cell wall breakdown, such as Penicillin.

Beta-lactam ring

A four-membered cyclic amide structure found in antibiotics like penicillins and cephalosporins.

Penicillin-binding proteins (PBPs)

Transpeptidase enzymes that beta-lactam antibiotics bind to in order to block transpeptidation and cause cell lysis.

Beta-lactamase

An enzyme produced by resistant bacteria that breaks a bond in the $\beta\text{-lactam}$ ring of penicillin to disable the molecule.

Penicilloic acid

The inactive molecule produced when $\beta\text{-lactamase}$ breaks the $\beta\text{-lactam}$ ring of penicillin.

Clavulanic acid

A suicide (irreversible) inhibitor of $\beta\text{-lactamase}$ enzymes that is co-formulated with $\beta\text{-lactam}$ antibiotics to overcome bacterial resistance.

Cephalosporins

Semisynthetic $\beta\text{-lactam}$ antibiotics modified in laboratories to improve effectiveness; there are currently five generations of this drug.

Cycloserine

A cell wall inhibitor that targets $D\text{-alanine}$ formation and blocks synthesis of $D\text{-Ala–D-Ala}$ precursors in the early cytoplasmic stage.

Bacitracin

A cell wall inhibitor that targets the bactoprenol lipid carrier, preventing its recycling and blocking the transport of peptidoglycan units.

Vancomycin

A glycopeptide that binds to $D\text{-Ala–D-Ala}$ on peptidoglycan precursors, preventing chain elongation and cross-linking outside the membrane.