Clindamycin Effect on Glycocalyx Production in Experimental Viridans Streptococcal Endocarditis

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Abstract
Abundant glycocalyx production by viridans streptococci in the rabbit model of endocarditis has been associated with delayed antimicrobial sterilization. Enzymatic digestion of the glycocalyx with dextranase enhances antibiotic activity. The effect of clindamycin (30 mg/kg, subcutaneous, three times daily)wasstudied in rabbits with experimental aortic valveendocarditis caused by high glycocalyx-producing viridans streptococci. Animals receiving c1indamycin had smaller vegetations that were sterilized more quickly than did controls or animals receiving penicillin or dextranase alone (P < .001). Penicillin plus dextranase treatment allowed greater bacterial killing than penicillin alone and did not differ significantly from c1indamycin treatment. Electron micrographs revealed markedly less cell-adherent glycocalyx on organisms grown in vitro treated with clindamycin versus penicillin and controls. It is hypothesized that clindamycin inhibits glycocalyx production in vivo, allowing better antimicrobial penetration in the infected cardiac vegetation.