The pneumococcus and the mouse protection test: inoculum, dosage and timing

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.