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Updated: Aug 13, 2026
Invasion of Human Cells by a Bacterial Pathogen
Published on: March 21, 2011
Penetration of antimicrobials into tissue culture cells and leucocytes
Abstract:
When exposed to HeLa cells in tissue culture for 72 hr., antimicrobials could be categorised into three groups characterised by cell associated concentrations much lower (ampicillin, cephalexin, cloxacillin, flucloxacillin, streptomycin and trimethoprim, all 14% or less), much higher (tetracycline and polymyxins) or approximating to those extracellularly (erythromycin, lincomycin, fusidic acid and gentamicin). For kanamycin, neomycin and sulphonamides, cell associated levels were between 24 and 47% and for penicillin G and cephaloridine were 66% of those extracellularly. With mouse peritoneal macrophages and human peripheral blood leucocytes cell associated levels for representative antibiotics were all lower after 3 hr. exposure than in the tissue culture cells. However, studies on the rate of release of cell associated antibiotic and of the effects of surface active agents indicated that the differences between cell types were due to loss of cell association during washing procedures to remove extracellular antibiotic. The effects of bactericidal antibiotics on survival of bacteria phagocytosed by mouse macrophages suggested that the cell association observed in tissue culture cells represented true intracellular penetration rather than mere binding to the cell surface. Within families of antibiotics, alterations to the molecule change cell penetration and the variations observed can not be explained merely in terms of simple diffusion, molecular size, dissociation constants, lipid solubility or protein binding.
Insights
Antimicrobials show varied cell association with HeLa cells and macrophages, indicating true intracellular penetration. Factors beyond simple diffusion influence antibiotic uptake by cells.
Area of Science:
- Microbiology
- Pharmacology
- Cell Biology
Background:
- Understanding antimicrobial cell association is crucial for effective drug delivery.
- Previous studies have not fully elucidated the mechanisms of antibiotic penetration into various cell types.
Purpose of the Study:
- To categorize antimicrobials based on their concentration within HeLa cells.
- To investigate antibiotic cell association in primary immune cells (macrophages and leucocytes).
- To determine if observed cell association represents true intracellular penetration.
Main Methods:
- Exposure of HeLa cells to various antimicrobials for 72 hours.
- Exposure of mouse peritoneal macrophages and human peripheral blood leucocytes to antibiotics for 3 hours.
- Analysis of cell-associated versus extracellular antimicrobial concentrations.
- Assessment of antibiotic effects on phagocytosed bacteria and release kinetics.
Main Results:
- Antimicrobials were grouped by cell-associated concentrations relative to extracellular levels (low, high, or similar).
- Cell-associated levels in macrophages and leucocytes were generally lower than in HeLa cells, attributed to washing artifacts.
- Bactericidal effects on intracellular bacteria confirmed true intracellular penetration, not just surface binding.
- Antibiotic variations in cell penetration could not be explained by simple diffusion, size, pKa, lipophilicity, or protein binding.
Conclusions:
- Antimicrobial cell association varies significantly, with some antibiotics penetrating cells effectively.
- Washing procedures can artifactually reduce measured cell-associated antibiotic levels.
- Intracellular penetration, rather than surface binding, is a key factor for some antibiotics.
- Molecular properties beyond simple physical-chemical parameters dictate antibiotic cell penetration.
