The introduction of the F-like resistance plasmid R124 into an ompC mutant of Escherichia coli K12 conferred altered sensitivity to a wide range of inhibitory agents. Sensitivity to ampicillin, chloramphenicol, ethionine, copper ions, deoxycholate, two fatty acids and colicins L and M was decreased by the plasmid. In contrast the plasmid-bearing ompC derivatives were more sensitive than the plasmid-free ompC mutant to erythromycin, cetyltrimethylammonium bromide and phenol. Introduction of R124 into the ompC strain also decreased the level of the OmpF protein and some (but not all) of the changed sensitivities listed above clearly resulted from this outer membrane protein deficiency. The presence in the ompC mutant of R124 (rather than the more efficient introduction of the plasmid into variants of the ompC strain) led to at least most of the changes described above because those tested were accentuated by the presence of a copy mutant of R124 and reversed by plasmid curing.

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