Aztreonam is a monocyclic beta-lactam antibiotic (a monobactam) originally isolated from Chromobacterium violaceum. It is resistant to beta-lactamases and is useful against gram-negative bacterial pathogens. It is not used to treat colds, viral or flu infections.

It has no useful activity against gram-positive bacteria or anaerobes, but has very broad spectrum against gram-negative aerobes, including Pseudomonas aeruginosa.