Development of a System to Monitor ompC Transcription in Escherichia coli Using a Green Fluorescence Protein Reporter System

Transient resistance to antibiotics is believed to be achieved through regulation of outer membrane proteins like OmpC. OmpC is upregulated in response to sublethal doses of the aminoglycoside kanamycin. The ompC promoter is regulated by the CpxA-CpxR system; here, we examine the necessity of CpxR regulation in OmpC expression following treatment with sublethal doses of streptomycin. Our study assessed ompC gene and protein expression in Escherichia coli wild type and cpxR mutant strains following 1 hour treatments with sublethal streptomycin, 3.5% NaCl or no treatment. To measure ompC expression, we used a reporter plasmid in which the ompC promoter was fused to the gene encoding green fluorescent protein (GFP). We intended to monitor ompC expression levels by measuring luminescence in treated and untreated cultures. Our results suggest that neither CpxR nor sublethal streptomycin treatment has an effect on expression of ompC. Since no difference in luminescence was observed between the three treatment groups for wild type and cpxR mutant E. coli, further optimization of the GFP reporter system is required.