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The pneumococcus and the mouse protection test: inoculum, dosage and timing
Abstract:
Intraperitoneal inoculation in mice of a S. pneumoniae type 3 in beef broth resulted in immediate growth in vivo as evidenced by bacterial counts in peritoneal washings and in blood. Treatment with penicillin 1 hour after inoculation reduced the bacterial counts in vivo; however, different doses of penicillin-G showed a similar effect as measured by bacterial counts, in spite of differences in their effect upon survival of the mice. Therefore, the effect of antibiotics in vivo in this model was better correlated with death/survival of the animals. For comparative purposes the ED50, i.e. the 50% effective dose, should be determined. The effect of cephalosporins, i.e. cefuroxime and cefotaxime, in this model highly depended upon timing of the antibiotic administration as related to inoculation.
Insights
Penicillin treatment reduced Streptococcus pneumoniae growth in mice, but survival outcomes were more sensitive to dosage than bacterial counts. Antibiotic effectiveness in vivo correlated better with animal survival, highlighting the need for ED50 determination.
Area of Science:
- Infectious Diseases
- Pharmacology
- Microbiology
Background:
- Streptococcus pneumoniae type 3 causes rapid intraperitoneal infection in mice.
- In vivo bacterial growth is evident through peritoneal washings and blood counts.
Purpose of the Study:
- To evaluate the in vivo efficacy of penicillin-G against Streptococcus pneumoniae in a murine model.
- To compare the correlation between bacterial counts, survival rates, and antibiotic dosage.
- To assess the impact of administration timing on cephalosporin efficacy (cefuroxime, cefotaxime).
Main Methods:
- Intraperitoneal inoculation of mice with Streptococcus pneumoniae type 3.
- Administration of penicillin-G at varying doses one hour post-inoculation.
- Monitoring bacterial counts in peritoneal washings and blood.
- Assessing animal survival rates.
- Evaluating cefuroxime and cefotaxime efficacy based on administration timing.
Main Results:
- Penicillin treatment significantly reduced in vivo bacterial counts.
- Different doses of penicillin-G exhibited similar effects on bacterial counts but varied impacts on survival.
- Antibiotic efficacy in vivo was more strongly correlated with animal survival than with bacterial load reduction.
- Cephalosporin efficacy was highly dependent on the timing of administration relative to inoculation.
Conclusions:
- In vivo antibiotic efficacy in this S. pneumoniae model is better reflected by survival data than by bacterial counts alone.
- The 50% effective dose (ED50) is a crucial metric for comparative antibiotic evaluation in vivo.
- Timing of antibiotic administration is a critical factor influencing the effectiveness of cephalosporins against S. pneumoniae.