Silver resistance in Escherichia coli R1

Area of Science:

• Microbiology
• Molecular Biology
• Environmental Science

Background:

• Escherichia coli strain R1, isolated from a burn patient treated with silver sulphadiazine, exhibits resistance to silver nitrate (AgNO3).
• Strain R1 harbors two large plasmids, pJT1 (83 kb) and pJT2 (77 kb).
• A silver-sensitive derivative, E. coli S1, was obtained by curing strain R1 of the pJT1 plasmid.

Purpose of the Study:

• To investigate the mechanism of silver resistance in Escherichia coli strain R1.
• To determine if silver accumulation differs between silver-resistant and silver-sensitive strains.

Main Methods:

• Utilized an Ag+-specific ion electrode to measure silver binding by cell suspensions.
• Employed transmission electron microscopy (TEM) and energy dispersive X-ray analysis (EDX) on whole cell mounts.
• Assessed hydrogen sulfide (H2S) production as a potential indicator.

Main Results:

• No significant difference in Ag+ binding was observed between resting cells of strains R1 and S1.
• TEM and EDX revealed that actively growing E. coli R1 cells did not accumulate silver, while E. coli S1 cells did.
• Both strains produced H2S, but its detection around colonies was strain-specific.

Conclusions:

• Actively growing silver-resistant E. coli R1 cells do not accumulate silver, indicating a non-accumulation-based resistance mechanism.
• The presence of the pJT1 plasmid is associated with silver resistance.
• Further research is needed to elucidate the precise molecular mechanism of silver resistance in E. coli.