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Staphylococcus aureus in continuous culture: a tool for the rational design of antibiotic treatment protocols
1Department of Biology, Emory University, Atlanta, Georgia, United States of America. klas.udekwu@ki.se
Abstract:
In vitro measures of the pharmacodynamics of antibiotics that account for the factors anticipated for bacteria in infected patients are central to the rational design of antibiotic treatment protocols. We consider whether or not continuous culture devices are a way to obtain these measures. Staphylococcus aureus PS80 in high-density continuous cultures were exposed to oxacillin, ciprofloxacin, vancomycin, gentamicin, daptomycin and linezolid. Contrary to results from low density retentostats as well as to predictions of traditional PK/MIC ratios, daily dosing with up to 100× MIC did not clear these cultures. The densities of S. aureus in these cultures oscillated with constant amplitude and never fell below 10(5) CFU per ml. Save for daptomycin "treated" populations, the densities of bacteria in these cultures remained significantly below that of similar antibiotic-free cultures. Although these antibiotics varied in their pharmacodynamic properties there were only modest differences in their mean densities. Mathematical models and experiments suggest that the dominant factor preventing clearance was wall-adhering subpopulations reseeding the planktonic population which can be estimated and corrected for. Continuous cultures provide a way to evaluate the potential efficacy of antibiotic treatment regimes in vitro under conditions that are more clinically realistic and comprehensive than traditional in vitro PK/PD indices.
Insights
High-density continuous cultures revealed that standard antibiotic dosing failed to eradicate Staphylococcus aureus. Adherent bacterial subpopulations continuously reseeded cultures, preventing clearance and highlighting limitations of traditional in vitro models.
Area of Science:
- Microbiology
- Pharmacology
- Infectious Diseases
Background:
- In vitro measures of antibiotic pharmacodynamics are crucial for designing effective treatment protocols.
- Traditional pharmacokinetics/minimum inhibitory concentration (PK/MIC) ratios may not accurately predict antibiotic efficacy in vivo.
- Continuous culture devices offer a potential method for more clinically relevant in vitro antibiotic testing.
Purpose of the Study:
- To evaluate the utility of high-density continuous culture devices for assessing antibiotic efficacy against Staphylococcus aureus.
- To determine if standard antibiotic dosing regimens can clear S. aureus in continuous cultures.
- To identify factors limiting antibiotic clearance in vitro.
Main Methods:
- High-density continuous cultures of Staphylococcus aureus (PS80) were exposed to various antibiotics (oxacillin, ciprofloxacin, vancomycin, gentamicin, daptomycin, linezolid).
- Antibiotic dosing was administered daily at up to 100 times the minimum inhibitory concentration (MIC).
- Bacterial densities were monitored, and mathematical models were used to analyze population dynamics.
Main Results:
- Daily antibiotic dosing, even at high concentrations, failed to clear S. aureus cultures.
- Bacterial densities oscillated and never dropped below 10^5 CFU/ml.
- Wall-adhering subpopulations were identified as a key factor reseeding planktonic populations and preventing complete clearance.
- Despite varying pharmacodynamic properties, antibiotics showed only modest differences in mean bacterial densities.
Conclusions:
- High-density continuous cultures provide a more clinically realistic in vitro model for evaluating antibiotic treatment efficacy compared to traditional methods.
- The presence of wall-adhering subpopulations significantly impacts antibiotic treatment outcomes.
- Further research using continuous cultures can refine antibiotic dosing strategies and improve treatment rationales.
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