Definition
Testing that checks a sample for viable microorganisms; distinct from endotoxin testing, which detects bacterial debris.
Sterility testing determines whether a sample contains viable bacteria or fungi. The pharmacopoeial method, USP chapter 71, uses membrane filtration or direct inoculation into growth media, followed by incubation for 14 days and inspection for growth. A negative result means no organisms were detected in the tested sample, which supports but cannot prove sterility of the whole batch. Sterility and endotoxin are separate measures: a solution can be sterile yet contain endotoxin from bacteria killed earlier, and filtration through a 0.22 µm membrane removes bacteria but not endotoxin. Research-grade lyophilised peptides are not usually supplied as sterile products, so aseptic technique during reconstitution matters for cell work.