Antimicrobial Agents

Bacterial cell walls are rigid structures built mainly from peptidoglycan. This mesh-like polymer gives bacteria strength and helps maintain cell shape. Because peptidoglycan synthesis is essential for growth, it is a major target for antibiotics.

Beta-lactam antibiotics, such as penicillin, stop peptidoglycan synthesis in actively growing cells. They have a four-membered beta-lactam ring that mimics the D-alanyl-D-alanine dipeptide, which is the natural substrate for transpeptidase, also...

Aminoglycosides are bactericidal antibiotics that stop bacteria by targeting the ribosome and disrupting protein synthesis. They are highly potent drugs made of amino-modified sugars linked by glycosidic bonds to an aminocyclitol core, such as 2-deoxystreptamine or streptamine. Their strong positive charge helps them bind tightly to the negatively charged phosphate backbone of ribosomal RNA, especially the 16S rRNA of the 30S subunit in the bacterial 70S ribosome.

These antibiotics act at the...

Fluoroquinolone antibiotics target bacterial DNA replication by blocking two key type II topoisomerases: DNA gyrase and topoisomerase IV. These enzymes help bacteria manage DNA supercoiling and separate chromosomes during replication. When they are disrupted, bacterial pathogens cannot copy DNA efficiently and infection can spread less effectively.

Fluoroquinolones are synthetic versions of quinolones. They work by stabilizing the short-lived DNA-enzyme cleavage complex, which stops strand...

Interferons block viral replication by shutting down protein synthesis and activating the cell’s antiviral defenses. Viruses need the host cell’s translational machinery to make proteins, because they do not have the machinery to do this on their own. When a virus is detected, infected cells release interferons, which are cytokines, or signaling proteins, that warn nearby uninfected cells.

Interferons bind to receptors on nearby cells and activate the JAK-STAT signaling pathway. This turns on...

Influenza viruses spread when new virions leave an infected cell and reach nearby cells. Influenza A and B are negative-sense, single-stranded RNA viruses with segmented genomes. They depend on two surface glycoproteins, hemagglutinin (HA) and neuraminidase (NA), to infect cells, make new viral particles, and release them.

HA starts infection by binding to sialic acid on the surface of host epithelial cells. This binding helps the virus enter the cell by receptor-mediated endocytosis. After...

Antiviral nucleoside inhibitors stop viruses by blocking DNA or RNA synthesis. These drugs are structural analogs, which means they look like natural nucleosides, the building blocks cells use to make genetic material. Because they resemble host nucleosides, they can interfere with viral polymerases and disrupt viral genome replication.

Acyclovir is a guanosine analog with a three-carbon acyclic side chain. It mainly targets herpes simplex virus type 1 (HSV-1), herpes simplex virus type 2...

Amphotericin B targets fungal cell membranes by binding to ergosterol, a sterol found mainly in fungal plasma membranes. Its amphipathic structure helps this selective binding. It has a hydrophobic polyene-lactone ring and a hydrophilic region with mycosamine and carboxylic acid groups. Weak binding to cholesterol can also affect human cells and helps explain the drug’s toxicity.

One way amphotericin B kills fungi is through pore formation. In this model, amphotericin B-ergosterol complexes...

Antibiotic resistance in bacteria happens when microbes evolve the ability to survive drugs that once killed them or slowed their growth. Genetic change and antibiotic exposure drive this process. Over time, useful treatments can stop working.

Bacteria can resist antibiotics in several ways. Some make drug-inactivating enzymes, such as beta-lactamases. Others use efflux pumps to push antibiotics out of the cell. Resistance can also come from mutations that change the drug target, from lower...

Helminth drugs work by attacking the weak points of parasitic worms. These anthelmintic medicines are different from drugs used against protozoa, because they are usually aimed at mature helminths rather than fast-dividing cells. They target the worm’s movement, glucose use, and microtubule structure to stop survival, reproduction, and location inside the host.

Benzimidazoles are broad-spectrum anthelmintics that block tubulin polymerization, which means they interfere with microtubules, the...

MRSA, or methicillin-resistant Staphylococcus aureus, is a major public health threat. It resists beta-lactam antibiotics because it carries the mecA gene inside the staphylococcal cassette chromosome mec, or SCCmec. The mecA gene makes penicillin-binding protein 2a, which reduces how well methicillin and related beta-lactam drugs can bind.

MRSA has spread into separate clonal lineages that affect both humans and animals. These lineages fit the One Health idea, which links human, animal, and...

HIV protease inhibitors block a key step in virus maturation. In human immunodeficiency virus (HIV), infected cells make two long precursor proteins called polyproteins. These are Gag and Gag-Pol. Gag provides the virus structure. Gag-Pol carries important viral enzymes, including reverse transcriptase, integrase, and protease.

After these polyproteins are made, they move to the host cell membrane. There, they help build an immature viral particle that buds from the cell surface. Budding...

Leishmaniasis is a parasitic disease caused by several Leishmania species. It affects millions of people each year and remains a major public health problem in endemic regions. Treatment often relies on pentavalent antimonials, including meglumine antimoniate and sodium stibogluconate.

The way these drugs work has not been fully clear. One important target is trypanothione reductase, or TR, an enzyme that helps keep Leishmania in redox balance. TR is not found in mammalian hosts, so it is a...