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Method of testing the susceptibility of Pneumocystis carinii to antimicrobial agents in vitro
Abstract:
Rat Pneumocystis carinii grown on lung-derived cell lines in tissue culture flasks and multiwell plates was tested for susceptibility to four antimicrobial agents currently being used in the treatment of human pneumocystosis. Standard criteria for organism quantitation, replication, viability, and inoculum size were established. Trimethoprim-sulfamethoxazole inhibited P. carinii growth at a concentration ratio of 1:19 microgram/ml, and pentamidine isethionate was active at 0.1 microgram/ml. alpha-Difluoromethylornithine, an inhibitor of polyamine biosynthesis, inhibited P. carinii at a concentration of 1 mM once erythrocytes (which are high in polyamine content) were removed from the inoculum; this effect could be overcome by the polyamine putrescine. Dapsone suppressed P. carinii replication at a dose of 0.1 microgram/ml, but this effect was lost after 72 h in culture. Overall, the reduction in P. carinii numbers with these drugs was relatively modest (45 to 84%), which is consistent with their lack of lethal effects on the organism in vivo. Thus, the system presented here should be helpful in developing new anti-P. carinii agents and in elucidating their mechanism of action.
Insights
This study evaluated four drugs against rat Pneumocystis carinii in cell culture. Trimethoprim-sulfamethoxazole and pentamidine showed activity, aiding the development of new anti-Pneumocystis agents.
Area of Science:
- Microbiology
- Infectious Diseases
- Pharmacology
Background:
- Pneumocystis pneumonia (PCP) is a serious opportunistic infection.
- Effective treatment relies on antimicrobial agents, but resistance and toxicity are concerns.
- In vitro models are crucial for evaluating drug efficacy and developing new therapies.
Purpose of the Study:
- To assess the in vitro susceptibility of rat Pneumocystis carinii to four key antimicrobial agents.
- To establish a reliable cell culture system for P. carinii drug screening.
- To provide a foundation for developing novel anti-Pneumocystis therapies.
Main Methods:
- Rat P. carinii was cultured on lung-derived cell lines.
- Standardized methods for organism quantitation, replication, and viability were implemented.
- Susceptibility testing was performed for trimethoprim-sulfamethoxazole, pentamidine isethionate, alpha-difluoromethylornithine, and dapsone.
Main Results:
- Trimethoprim-sulfamethoxazole inhibited growth at 1:19 µg/ml; pentamidine at 0.1 µg/ml.
- alpha-Difluoromethylornithine showed inhibition at 1 mM without erythrocytes, reversible by putrescine.
- Dapsone suppressed replication at 0.1 µg/ml, but efficacy diminished after 72 hours.
Conclusions:
- The established cell culture system effectively evaluates P. carinii susceptibility to antimicrobials.
- Current agents demonstrated modest reductions in P. carinii, correlating with in vivo observations.
- This model system is valuable for discovering new anti-P. carinii drugs and understanding their mechanisms.