Bactericidal

Bactericidal describes agents or mechanisms that kill bacteria rather than merely inhibiting their growth. Bactericidal activity leads to a decrease in viable bacterial count, while bacteriostatic agents halt replication and rely on the host immune system to clear the infection. The distinction is not absolute; some drugs are bactericidal for certain organisms or at higher concentrations and bacteriostatic for others.

Common mechanisms of bactericidal action include disruption of cell wall synthesis (for example, beta-lactams such as penicillins and cephalosporins, and glycopeptides like vancomycin), disruption of cell membrane integrity (polymyxins, daptomycin), interference with nucleic acid synthesis (fluoroquinolones, rifamycins), and inhibition of essential metabolic or enzymatic processes (certain aminoglycosides and related agents). The bactericidal property of an agent can vary with organism, drug concentration, and environmental conditions.

In vitro and clinical testing often use the minimum bactericidal concentration (MBC) alongside the minimum inhibitory concentration (MIC). An MBC/MIC ratio of about 4 or less is commonly taken to indicate bactericidal activity, though this is not universal.

Clinically, bactericidal antibiotics are preferred for severe infections such as meningitis, endocarditis, bacteremia, and infections in immunocompromised patients, where rapid bacterial kill is advantageous. Bacterial resistance can modulate efficacy, through mechanisms like target modification or drug degradation, highlighting the ongoing need for appropriate antibiotic selection and stewardship.