Expression of genes associated with antibiotic extrusion in Pseudomonas aeruginosa.

We cloned the gene(s) associated with multiantibiotic resistance in Pseudomonas aeruginosa from a mutant with elevated drug extrusion. The strain harboring cloned gene accumulated less amount of ofloxacin than the strain without the clone. By using Southern and northern blot analyses, we investigated whether multiantibiotic resistance is caused by gene amplification or overexpression. We found that all our multiantibiotic resistance is caused by gene amplification or overexpression. We found that all our multiantibiotic resistant mutants isolated earlier overexpressed mRNA homologous to the cloned gene(s). Overexpression of the 41 KDa and 110 KDa inner and the 50 KDa outer membrane proteins were detected. Other multiantibiotic resistant mutants including the nalB mutant overexpressed the mRNA and the membrane proteins, but the nfxB and nfxC mutants did little. We concluded that low antibiotic accumulation in the multiantibiotic resistant mutants is attributable to overexpression of the antibiotic extrusion machinery.