1. Penicillin (PN), chloramphenicol (CM), or tetracycline (TC) resistant variant of
Streptococcus faecalis in this paper was more sensitive to other kinds of antibiotics than its parent strain, except that PN or TC resistant strain was cross resistant to synthetic PNs or oxytetracycline respectively.
2. During a year storage of the strain in stab culture or in starch powder the resistant value of PN dropped down remarkedly, though those of CM and TC never did.
3. Drop of resistant value dering serial transfer of the strains in drug free media appeared even after only first passage in case of PN, though in CM it did not after tenth but after twentieth and in TC not at least before twentieth passages.
4. By addition of desoxycholate to media the PN resistance was artificially removed, whereas the CM or TC resistance was still stable.
5. Moreover, the PN or CM resistance was decreased by acriflavine treatment, though the TC resistance stood unchanged, and the frequency of occurance of decreased resistant strain was higher than normal transfer procedure.
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