Therapy of experimental infective endocarditis due to antibiotic-tolerant Lactobacillus plantarum-bactericidal synergy of penicillin plus gentamicin. Correlation of in vitro susceptibility studies with in vivo efficacy.

Infective aortic valve endocarditis (IE) was induced in 40 rabbits with a penicillin (PNC)-tolerant, gentamicin (GM)-resistant strain of Lactobacillus plantarum; this isolate was synergistically killed in vitro by PNC + GM. The in vivo relevance of the in vitro observations was examined by determining the rates of eradication of endocardial L. plantarum by PNC versus PNC + GM. Mean vegetation L. plantarum titers were significantly lower (p less than 0.05) in PNC + GM treated rabbits versus both PNC-treated and control rabbits by 48 h of therapy. Also, PNC + GM more rapidly sterilized vegetations as compared to controls (p less than 0.025) and PNC-treated rabbits (p less than 0.05). Thus, in vivo antibiotic efficacy paralleled in vitro bactericidal studies, and may partially explain the relatively refractory nature of lactobacillary IE in humans treated with single beta-lactam antibiotics.