Cycloserine

Cycloserine is a broad-spectrum antibiotic used mainly to treat tuberculosis. It inhibits bacterial cell-wall synthesis by disrupting enzymes that build peptidoglycan.

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D-alanine racemase: An enzyme that converts L-alanine into D-alanine, a building block of bacterial peptidoglycan. Cycloserine inhibits this enzyme, reducing the D-alanine supply for cell-wall assembly.
Multidrug-resistant tuberculosis: Tuberculosis caused by bacteria resistant to at least isoniazid and rifampicin. Cycloserine is used as a second-line drug in regimens for resistant tuberculosis.
Cycloserine-induced neurotoxicity: Neurological or psychiatric adverse effects associated with cycloserine, including seizures, confusion, and mood changes. These effects are the main reason cycloserine treatment needs careful clinical monitoring.
Streptomyces orchidaceus: A soil-dwelling actinomycete from which cycloserine was isolated. This microorganism was the original natural source of cycloserine.
D-alanine–D-alanine ligase: An enzyme that joins two D-alanine molecules during bacterial peptidoglycan synthesis. Cycloserine inhibits this second target, preventing formation of a key cell-wall precursor.
Extensively drug-resistant tuberculosis: A severe form of drug-resistant tuberculosis with resistance to additional key medicines. Cycloserine may contribute to treatment when standard tuberculosis drugs cannot be relied upon.
Pyridoxine: Vitamin B6, a cofactor in amino-acid metabolism and neurotransmitter synthesis. Pyridoxine is often given with cycloserine to reduce neurological toxicity.
Antibiotic discovery: The identification and development of substances that inhibit or kill microorganisms. Cycloserine emerged from the search for antibiotics produced by soil microorganisms.
Peptidoglycan: A mesh-like polymer of sugars and peptides that gives most bacterial cell walls strength and shape. Cycloserine disrupts the precursor chemistry needed to build this structural mesh.
Tuberculosis treatment: The use of antimicrobial drugs in combinations and over extended periods to cure tuberculosis. Cycloserine is reserved for selected regimens rather than routine first-line treatment.