Cross-resistance of Escherichia coli B/r to cis-platinum (II) diamminochloride, UV light and alkylating agents.

Gradual transfers of the strain Escherichia coli B/r on M9 agar with increasing concentrations of cis-platinum (II) diamminochloride (cis-Pt(II)) yielded a resistant strain SM 405 capable of growing on liquid M9 medium containing 250 muM cis-Pt(II). The parent strain Escherichia coli B/r is completely inhibited in both division and growth at cis-Pt(II) concentrations as low as 30 muM. The resistant mutant has a longer doubling time than the parent strain. No other differences were found between the two strains. To elucidate the nature of the resistance, the effect of cis-Pt(II) on the survival of the two strains was compared with that of nitrogen mustard, UV light and ethyl methanesulphonate (EMS). The resistant strain SM 405 was found to be more hardened against the lethal action of UV light and nitrogen mustard but less so against EMS. It had also a higher ability of a host-cell reactivation of UV-irradiated phage T3. The different resistance of the B/r and SM 405 strains is probably due to a mutation increasing the effectiveness of the excision repair in the latter.