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Oxacillin killing curve patterns of Staphylococcus aureus isolates by agar dilution plate count method
Antimicrobial Agents and Chemotherapy
|January 1, 1987
Summary
Oxacillin killing dynamics vary significantly between Staphylococcus aureus strains, challenging the reliability of traditional methods like MBCs and MBC/MIC ratios for characterizing bacterial tolerance. This study reveals strain-dependent dynamics in oxacillin action.
Area of Science:
- Microbiology
- Pharmacodynamics
- Bacterial resistance
Background:
- Staphylococcus aureus is a significant human pathogen.
- Understanding antibiotic dynamics is crucial for effective treatment.
- Persister cells contribute to treatment failure and relapse.
Purpose of the Study:
- To investigate the bactericidal dynamics of oxacillin against Staphylococcus aureus isolates.
- To characterize the influence of persister cell percentages on oxacillin activity.
- To evaluate the utility of traditional antimicrobial susceptibility testing (AST) methods.
Main Methods:
- Agar dilution plate count method was employed.
- Four Staphylococcus aureus isolates with varying persister percentages were used.
- Killing curves were generated to analyze bacterial dynamics over time.
Main Results:
- Reproducible killing curve patterns were observed for each isolate.
- The paradoxical effect, where higher antibiotic concentrations lead to less killing, was noted.
- Strain-dependent dynamics in oxacillin killing were evident.
Conclusions:
- The observed dynamics suggest the 'tolerance phenomenon' may be artifactual.
- Minimum Bactericidal Concentrations (MBCs) and MBC/MIC ratios are not useful for characterizing S. aureus isolates.
- Strain-specific responses to oxacillin necessitate tailored therapeutic strategies.