Cellular uptake and intraphagocytic activity of the new fluoroquinolone AF 3013 against Klebsiella pneumoniae.

ABSTRACT

The entry of an antibiotic into phagocytes is a prerequisite for its intracellular bioactivity against susceptible facultative or obligatory intracellular microorganisms. AF 3013 is a new fluoroquinolone, and its uptake into and elimination from mouse peritoneal macrophages, together with its effects on phagocytic and antimicrobial mechanisms against Klebsiella pneumoniae, were investigated. AF 3013 efficiently penetrated into phagocytic cells at all concentrations tested. The uptake proceeded rapidly and was energy independent, since it was not affected by cell viability, environmental temperature or the addition of a metabolic inhibitor. Therefore, a possible passive transmembrane diffusion mechanism might be proposed. The elution of AF 3013 from macrophages occurred relatively slowly; in fact, 60 min after the removal of extracellular AF 3013, nearly 40% of the drug still remained in the phagocytes. Exposure to 1 MIC of AF 3013 significantly enhanced macrophages phagocytosis and increased intracellular bactericidal activity against K. pneumoniae. Following preexposure of macrophages to 1 MIC of AF 3013, there was a significant increase in both phagocytosis and killing, compared with the controls, indicating the ability of AF 3013 to interact with biological membranes and remain active within phagocytes. Preexposure of Klebsiella to AF 3013 made the bacteria more susceptible to the bactericidal mechanisms of macrophages than untreated organisms.