Bacterial Persistence in Streptococcal Endocarditis Due to Thiol-Requiring Mutants

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Abstract
Defective strains of Streptococcus were isolated from cardiac valves or blood cultures from three patients with bacterial endocarditis. These strains did not grow on the usual media under aerobic or anaerobic conditions. Enrichment of media with L-cysteine, reduced glutathione, thioglycollic acid, or dithiothreitol was required for growth. Deficient mutants with the same requirements for thiol groups were selected in vitro from streptococci of Group N by a two-step procedure. In an experimental model in mice, the combination of penicillin and streptomycin did not act synergistically against these deficient streptococci as it did against normal strains. The physiologic properties of the defective streptococci make it difficult to isolate them from clinical specimens and to diagnose and treat infections in which they are the causative organism.

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