Related Experiment Video
Updated: Sep 25, 2026
Development of a Polymicrobial Colony Biofilm Model to Test Antimicrobials in Cystic Fibrosis
Published on: September 20, 2024
Accumulation and activity of cethromycin (ABT-773) within human polymorphonuclear leucocytes
I García1, A Pascual, S Ballesta
1Department of Microbiology, School of Medicine, Seville, Spain. igarcia1@us.es
Objectives:
To evaluate the penetration of ketolide cethromycin (ABT-773) into human polymorphonuclear leucocytes (PMNs) and its intracellular activity.
Methods:
The uptake of radiolabelled cethromycin by PMNs was determined by a velocity gradient centrifugation technique. The activity of cethromycin against intracellular Staphylococcus aureus ATCC 25923 in PMNs was also evaluated.
Results:
The cellular to extracellular concentration (C/E) ratio for cethromycin was >200 at an extracellular concentration of 2 mg/L. The uptake of cethromycin into PMNs was rapid and saturable. Cethromycin was slowly released from the loaded PMNs (cell associated drug>50% after 2 h of incubation). Intracellular penetration was significantly affected by the environmental temperature (C/E ratio at 4 degrees C and 37 degrees C: 13 +/- 6 and 226 +/- 31, respectively; P < 0.05), by cell viability (C/E ratio for dead and viable cells: 100 +/- 38 and 226 +/- 31, respectively; P < 0.05), by pH (C/E ratio was significantly increased at basic pH) and by the metabolic inhibitors 2,4-dinitrophenol and carbonyl cyanide m-chlorophenylhydrazone. The intracellular accumulation of cethromycin also decreased significantly when cells were activated with phorbol myristate acetate or opsonized zymosan. These data indicate that a potentially active mechanism could be involved in the uptake of cethromycin by PMNs. At high extracellular concentrations of 5 and 10 mg/L, cethromycin showed significant intracellular activity against S. aureus.
Conclusions:
Cethromycin achieves high intracellular concentrations within human PMNs, remaining active intracellularly.
Insights
Ketolide cethromycin rapidly penetrates human polymorphonuclear leucocytes (PMNs), achieving high intracellular concentrations. This antibiotic demonstrates significant intracellular activity against Staphylococcus aureus within PMNs.
Area of Science:
- Pharmacology
- Microbiology
- Cell Biology
Background:
- Polymorphonuclear leucocytes (PMNs) are critical in combating bacterial infections.
- Understanding intracellular antibiotic penetration is key to optimizing treatment strategies.
Purpose of the Study:
- To assess the cellular uptake and intracellular activity of the ketolide antibiotic cethromycin (ABT-773) in human PMNs.
- To investigate the mechanisms influencing cethromycin penetration into PMNs.
Main Methods:
- Quantified cethromycin uptake in PMNs using radiolabeling and velocity gradient centrifugation.
- Evaluated the activity of intracellular cethromycin against Staphylococcus aureus.
- Assessed the impact of temperature, pH, cell viability, and metabolic inhibitors on cethromycin uptake.
Main Results:
- Cethromycin exhibited a high cellular to extracellular concentration (C/E) ratio (>200) in PMNs, indicating rapid and saturable uptake.
- Intracellular penetration was significantly influenced by temperature, cell viability, pH, and metabolic inhibitors, suggesting an active uptake mechanism.
- Cethromycin demonstrated potent intracellular activity against Staphylococcus aureus at higher concentrations.
Conclusions:
- Cethromycin effectively penetrates human PMNs, reaching high intracellular concentrations.
- The antibiotic retains significant antimicrobial activity within these immune cells, supporting its potential in treating intracellular bacterial infections.
