Amoxycillin-resistant oral streptococci and experimental infective endocarditis in the rabbit.

The ability of three amoxycillin-resistant strains of Streptococcus sanguis 254, 24 and 297 (MIC 40 mg/L) to cause infective endocarditis (IE) in the rabbit was investigated. These strains all produced infection in the rabbit, as did an antibiotic sensitive control strain NCTC 7864. Prophylactic amoxycillin (400 mg/kg body weight) administered one hour before bacterial challenge prevented 80% of the animals developing IE irrespective of the challenging strain. It is concluded that amoxycillin-resistant strains of S. sanguis can cause IE and that amoxycillin prophylaxis can still be effective against these bacteria.