Antibiotic therapy of experimental Staphylococcus epidermidis endocarditis

Area of Science:

• Infectious Diseases
• Microbiology
• Pharmacology

Background:

• Endocarditis is a serious infection, and methicillin-resistant Staphylococcus epidermidis (MRSE) poses a significant therapeutic challenge.
• The isolate used demonstrated resistance to various semisynthetic penicillins and cephalosporins, impacting minimum inhibitory and bactericidal concentrations.

Purpose of the Study:

• To evaluate the efficacy of different antibiotic regimens in treating experimental endocarditis caused by MRSE in a rabbit model.
• To compare the effectiveness of vancomycin, gentamicin, rifampin, nafcillin, cephalothin, and cefamandole in reducing bacterial burden in cardiac vegetations.

Main Methods:

• Experimental endocarditis was induced in rabbits using a methicillin-resistant Staphylococcus epidermidis isolate.
• Animals were treated for 2 or 7 days with various antibiotics, including nafcillin, cephalothin, cefamandole, vancomycin, rifampin, and gentamicin.
• Bacterial counts in vegetations were assessed, and antibiotic susceptibility of isolates was monitored.

Main Results:

• No significant difference in bacterial load was observed between control and cephalosporin/nafcillin treated groups after 7 days.
• Vancomycin, gentamicin, and rifampin significantly reduced bacterial numbers in vegetations compared to controls and cephalosporins/nafcillin.
• Rifampin demonstrated superior sterilization of vegetations after 2 days, and both rifampin and gentamicin were highly effective after 7 days.

Conclusions:

• Rifampin, vancomycin, and gentamicin may be more effective treatments for MRSE endocarditis in humans than traditional cephalosporins or semisynthetic penicillins.
• The emergence of rifampin-resistant mutants was noted in one case, highlighting the need for careful monitoring.
• These findings support the potential use of vancomycin, gentamicin, or rifampin for treating challenging MRSE endocarditis cases.