Uptake, transport, delivery, and intracellular activity of antimicrobial agents.

Antibiotic interactions with cells, including polymorphonuclear neutrophils, may influence therapeutic outcomes. Selected microbes (e.g., Legionella pneumophila) may survive ingestion by polymorphonuclear neutrophils and are thus protected from the action of antimicrobial agents that remain extracellular. Antibiotics that penetrate the cell can kill these microbes. Certain antibiotics are concentrated inside phagocytes, and when the phagocyte migrates toward the site of infection, the antibiotic-loaded cell carries the active agent to the infecting microbes. Active antibiotic may be released when the short-lived phagocyte dies. Even microbes considered to be extracellular pathogens, such as pneumococci, may survive high concentrations of antibiotic by entering cells. Antibiotics that penetrate and are active in cells may aid in enhancing therapeutic outcomes and in eliminating the carrier state for some pathogens.