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Cellular uptake and intracellular activity of antibiotics against Haemophilus influenzae type b
Abstract:
The ability of penicillins and chloramphenicol to enter human polymorphonuclear leukocytes (PMNLs) and their antibacterial activity against intracellular Haemophilus influenzae type b were studied. Penicillin was excluded whereas chloramphenicol was concentrated in PMNLs; chloramphenicol uptake was not dependent on PMNL energy and was not competitively inhibited by unlabeled drug. PMNLs that had phagocytized opsonized H. influenzae type b were examined after incubation for 24 hr. In the absences of antibiotics, intact intracellular H. influenzae type b organisms were observed in PMNLs by electron microscopy. These PMNLs contained 10(4.5) colony-forming units (cfu) of H. influenzae type b. Addition of penicillin or ampicillin at four, 20, or 40 times the minimal bactericidal concentration (MBC) decreased this density from 10(4.5) to 10(3.5) cfu. In contrast, addition of chloramphenicol at four times the MBC reduced the density to approximately 100 cfu; at 10 times the MBC it reduced the density to approximately 10 cfu. Thus, lipid-soluble antibiotics such as chloramphenicol are concentrated and are bioactive within PMNLs. Such antibiotics may have a significant advantage at the cellular level.
Insights
Chloramphenicol effectively enters human polymorphonuclear leukocytes (PMNLs) and kills intracellular Haemophilus influenzae type b. Penicillin showed limited efficacy against intracellular bacteria within PMNLs.
Area of Science:
- Pharmacology
- Microbiology
- Cell Biology
Background:
- Human polymorphonuclear leukocytes (PMNLs) are crucial for combating bacterial infections.
- Intracellular bacteria, such as Haemophilus influenzae type b, pose a therapeutic challenge.
- Understanding antibiotic penetration into PMNLs is vital for effective treatment.
Purpose of the Study:
- To investigate the uptake of penicillins and chloramphenicol by human PMNLs.
- To evaluate the antibacterial activity of these antibiotics against intracellular Haemophilus influenzae type b.
Main Methods:
- PMNLs were incubated with Haemophilus influenzae type b and varying concentrations of penicillins and chloramphenicol.
- Antibiotic uptake by PMNLs was assessed.
- Bacterial viability within PMNLs was determined using colony-forming unit (CFU) counts and electron microscopy.
Main Results:
- Penicillin was largely excluded from PMNLs, showing minimal effect on intracellular bacteria.
- Chloramphenicol was concentrated within PMNLs, independent of cellular energy.
- Chloramphenicol significantly reduced intracellular Haemophilus influenzae type b viability in a dose-dependent manner.
Conclusions:
- Lipid-soluble antibiotics like chloramphenicol demonstrate superior penetration and bioactivity within PMNLs.
- Chloramphenicol's ability to concentrate in PMNLs offers a potential advantage for treating intracellular bacterial infections.
- These findings highlight the importance of antibiotic physicochemical properties for cellular-level efficacy.