bactericidal

A bactericidal drug is one that actually kills bacteria, rather than merely freezing them in place. The Latin root means bacteria-killing. In everyday terms, a bactericidal antibiotic is the difference between executing the invaders and simply putting them under house arrest.

Different bactericidal classes kill in different ways: beta-lactams burst the cell by wrecking its wall, aminoglycosides corrupt protein synthesis fatally, and fluoroquinolones shatter the DNA. The killing is quantified in the lab by the minimum bactericidal concentration, the lowest drug level that kills the great majority of an organism, as opposed to the MIC, which only stops growth.

Bactericidal action matters most when the patient's own defences cannot finish the job: in meningitis, endocarditis, severe sepsis, or in people with weakened immune systems. In an otherwise healthy patient with a mild infection, a bacteriostatic drug that merely halts growth is often perfectly adequate, because the immune system clears the suppressed organisms. The bactericidal-versus-bacteriostatic distinction is therefore a guide, not a rigid hierarchy, and can even shift with concentration or organism.