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Effect of penicillin G on Staphylococcus aureus phagocytosed by human monocytes
Abstract:
The effect of penicillin G on Staphylococcus aureus after phagocytosis by human monocytes was compared with the effect on nonphagocytosed bacteria. Intracellular S. aureus was obtained by incubation of monocytes and preopsonized S. aureus for 3 min at 37 C; phagocytosis was stopped by cooling the test tubes in crushed ice. Nonphagocytosed bacteria were removed by differential centrifugation followed by two washes of the cells. Morphological studies with lysostaphin confirmed the intracellular localization of approximately 70% of the bacteria after this procedure. The antibacterial activity of penicillin G was assessed by incubation of monocytes containing ingested S. aureus with the drug at 37 C, and determination of the number of viable cell-associated bacteria was assessed microbiologically at various intervals. Inactivation of the intracellular killing mechanism of the monocytes by omission of serum during incubation allowed measurement of the effect of penicillin G apart from the bactericidal activity of the cells. The effect of penicillin G on nonphagocytosed bacteria was assessed after incubation of preopsonized S. aureus in medium with the drug. The results show that the effect of penicillin G on intracellular S. aureus is two to seven times stronger than the effect on nonphagocytosed S. aureus.
Insights
Penicillin G is significantly more effective against Staphylococcus aureus inside human monocytes than against bacteria outside cells. This finding highlights the enhanced potency of penicillin G against intracellular bacteria.
Area of Science:
- Immunology
- Microbiology
- Pharmacology
Background:
- Human monocytes play a crucial role in the innate immune response against bacterial infections.
- Staphylococcus aureus is a common pathogen that can evade immune defenses by residing within host cells.
- Penicillin G is a widely used antibiotic, but its efficacy against intracellular bacteria requires further investigation.
Purpose of the Study:
- To compare the antibacterial activity of penicillin G against intracellular Staphylococcus aureus within human monocytes versus non-phagocytosed bacteria.
- To elucidate the impact of intracellular localization on the efficacy of penicillin G.
Main Methods:
- Human monocytes were incubated with preopsonized Staphylococcus aureus to facilitate phagocytosis.
- Intracellular bacteria were isolated by differential centrifugation and confirmed via morphological studies.
- Antibacterial activity of penicillin G was assessed by incubating monocytes with ingested bacteria or non-phagocytosed bacteria at 37°C.
- Monocyte's intrinsic killing mechanisms were inactivated to isolate the effect of penicillin G.
Main Results:
- Penicillin G demonstrated significantly enhanced activity against intracellular Staphylococcus aureus compared to extracellular bacteria.
- The potency of penicillin G against intracellular S. aureus was found to be two to seven times greater than against non-phagocytosed S. aureus.
- This enhanced effect was observed independently of the monocytes' own bactericidal activity.
Conclusions:
- Intracellular localization within human monocytes potentiates the antibacterial effect of penicillin G against Staphylococcus aureus.
- These findings suggest that penicillin G may be a more effective therapeutic agent for intracellular S. aureus infections than previously recognized.
- Further research into host-pathogen-drug interactions is warranted to optimize antibiotic strategies for intracellular bacterial infections.