The sequence homology of clindamycin resistance determinants was studied in 42 clindamycin re-sistant Bacteroides strains isolated from different geographical areas, that is Gifu, Nagasaki, Fuku-oka, Ehime, Toyama, Tokyo and Saitama. These isolates were surveyed for homology with the clindamycin resistance determinant of the plasmid pBFTM 10. The clindamycin resistance DNA probe used in colony hybridization were pMJS 100, a plasmid derivative containing an EcoRl B fragment of pBFTM 10 cloned into E. coli. All of the strains resistant to clindamycin also carried tetracycline resistance except one strain and a total of 39 of 42 clindamycin resistant strains showed homology with the clindamycin resistance determinant of pBFTM 10. These data revealed that the same clin-damycin resistance determinant dominant in U. S. A. is also widely distributed in japan.

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Bactericidal activities of penicillins against S. faecalis in single and mixed cultures with β-lactamase producing gram-negative bacilli were investigated by measurement of minimum bactericidal concen-tration (MBC).
Bactericidal effects of ampicillin and amoxicillin against S. faecalis were remarkably reduced in most mixed cultures. That of piperacillin (PIPC) was reduced in mixed cultures with strains producing constitutive β-lactamase, but were not reduced in the case of mixed cultures with inducible β-lacta-mase producing strains.
The stability of these penicillins against β-lactamases of inducible β-lactamase producing strains used as the combination partner in mixed cultures and their inducer activities for β-lactamase production were also studied. Though all penicillins were stable to various β-lactamases, there was a appreciable difference in the inducibility of these penicillins. PIPC hardly induced β-lactamase production, while other penicillins showed very high inducer activities.
Accordingly, it seemed that the difference in the bactericidal effects of penicillins against S. faecalis in mixed cultures was attributable to the degree of inactivation of penicillins by β-lactamase derived from the combination partner based on their inducer activities for β-lactamase production.

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