Experimental pneumococcus infection in mice: correlation of bactericidal activity in vitro with the effect in vivo...

Area of Science:

• Microbiology
• Pharmacology
• Infectious Diseases

Background:

• Streptococcus pneumoniae is a significant bacterial pathogen.
• Aminoglycosides are a class of antibiotics used to treat bacterial infections.
• Understanding the in vivo efficacy and in vitro activity correlation of aminoglycosides is crucial for optimizing treatment strategies.

Purpose of the Study:

• To evaluate the in vivo efficacy of gentamicin, tobramycin, and netilmicin against Streptococcus pneumoniae type 3 in a murine model.
• To correlate the in vivo effect with in vitro bactericidal activity, focusing on bactericidal rates.
• To identify pharmacokinetic parameters that best correlate with in vitro bactericidal activity.

Main Methods:

• An experimental mouse model was established using intraperitoneal inoculation of Streptococcus pneumoniae type 3.
• Single-dose administration of gentamicin, tobramycin, and netilmicin was employed.
• In vitro activity was assessed by determining minimal inhibitory concentrations (MICs) and minimal bactericidal concentrations (MBCs).
• In vivo efficacy was measured by the 50% effective dose (ED50).
• Pharmacokinetic parameters, including peak serum concentrations, were investigated.

Main Results:

• Minimal Inhibitory Concentrations (MICs) and Minimal Bactericidal Concentrations (MBCs) were 12.5 µg/ml for netilmicin and 25 µg/ml for gentamicin and tobramycin.
• All three aminoglycosides demonstrated excellent in vitro bactericidal activity, even at 1/4 MIC.
• Tobramycin exhibited a lower bactericidal rate compared to gentamicin and netilmicin.
• In vivo efficacy (ED50) correlated well with the relative in vitro bactericidal activities.
• Peak serum concentrations showed the strongest correlation with in vitro bactericidal rates among the investigated pharmacokinetic parameters.

Conclusions:

• Netilmicin demonstrated superior in vitro and in vivo activity against Streptococcus pneumoniae type 3 compared to gentamicin and tobramycin.
• Peak serum concentration is a key pharmacokinetic parameter predicting the in vitro bactericidal efficacy of aminoglycosides.
• These findings support the importance of considering both in vitro bactericidal rates and peak serum concentrations when selecting aminoglycosides for treating S. pneumoniae infections.