The recovery of penicillin-G-sensitive variants of a resistant staphylococcus from the blood and tissues of two dogs with experimental endocarditis, infected with the resistant parent strain, has been previously reported.1 In one dog the number of sensitive variants recovered from the blood stream gradually increased during the infection in proportion to the resistant ones for reasons which were not apparent; in the other they were found in small numbers only at autopsy. These sensitive variants have retained their penicillin sensitivity after five years' passage through penicillin-free broth and after passage through untreated dogs and dogs treated with tetracycline.2In view of widespread interest in ecological relationships between antibiotic-sensitive and antibiotic-resistant bacteria, the finding of these penicillin-sensitive mutants in vivo provided an opportunity for artificially mixing two closely related variants of the same strain and studying their fate when inoculated into dogs. We have accordingly injected mixtures of
HAMBURGER M, SCHAFER NA, AVERY LW. Study of Experimental Staphylococcal Endocarditis in Dogs: IV. Distribution of Penicillin-G-Sensitive and -Resistant Staphylococci in Tissues, Following Inoculation of Mixtures of the Two Variants. Arch Intern Med. 1963;112(5):755–759. doi:10.1001/archinte.1963.03860050142017
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