Silver-resistant mutants of Escherichia coli display active efflux of Ag+ and are deficient in porins

被引:268
作者
Li, XZ
Nikaido, H
Williams, KE
机构
[1] UNIV SASKATCHEWAN,DEPT MICROBIOL,SASKATOON,SK S7N 5E5,CANADA
[2] UNIV SASKATCHEWAN,DIV INFECT DIS,SASKATOON,SK S7N 5E5,CANADA
[3] UNIV CALIF BERKELEY,DEPT MOL & CELL BIOL,BERKELEY,CA 94720
关键词
D O I
10.1128/JB.179.19.6127-6132.1997
中图分类号
Q93 [微生物学];
学科分类号
071005 ; 100705 ;
摘要
Silver-resistant mutants were selected by stepwise exposure of silver-susceptible clinical strains of Escherichia coli, two of which did not contain any plasmids, to either silver nitrate or silver sulfadiazine. These mutants showed complete cross-resistance to both compounds, They showed low-level cross-resistance to cephalosporins and HgCl2 but not to other heavy metals, The Ag-resistant mutants had decreased outer membrane (OM) permeability to cephalosporins, and all five resistant mutants tested were deficient in major porins, either OmpF or OmpF plus OmpC, However, the well-studied OmpF- and/or OmpC-deficient mutants of laboratory strains K-12 and B/r were not resistant to either silver compound, Resistant strains accumulated up to fourfold less (AgNO3)-Ag-110m than the parental strains, The treatment of cells with carbonyl cyanide m-chlorophenylhydrazone increased Ag accumulation in Ag-susceptible and -resistant strains, suggesting that even the wild-type Ag-susceptible strains had an endogenous Ag efflux activity, which occurred at higher levels in Ag-resistant mutants. The addition of glucose as an energy source to starved cells activated the efflux of Ag, The results suggest that active efflux, presumably coded by a chromosomal gene(s), may play a major role in silver resistance, which is likely to be enhanced synergistically by decreases in OM permeability.
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页码:6127 / 6132
页数:6
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