Purification of a 54-kilodalton protein (OprJ) produced in NfxB mutants of Pseudomonas aeruginosa and production of a monoclonal antibody specific to OprJ.

The 54-kDa outer membrane protein (designated OprJ) of a norfloxacin-resistant nfxB mutant of Pseudomonas aeruginosa PAO1 was purified by ion-exchange high-performance liquid chromatography. Mobility of OprJ in sodium dodecyl sulfate-polyacrylamide gel electrophoresis was not affected by reduction and heating. A murine monoclonal antibody (MAb) against OprJ was prepared to investigate existence of this protein in fluoroquinolone-susceptible and -resistant strains of P. aeruginosa. Western blot (immunoblot) analysis with this MAb revealed a single band at the position corresponding to OprJ in outer membrane proteins of NfxB mutants derived from clinical isolates. However, the MAb did not react with any outer membrane proteins of the respective parent strains. Complementation of the NfxB mutation by transformation with plasmid pNF111, which contained the wild-type nfxB gene, led to disappearance of the single band corresponding to OprJ. The existence of OprJ was associated with fluoroquinolone resistance. Furthermore, the MAb did not react with any outer membrane proteins of other fluoroquinolone-resistant nalB and nfxC mutants. These results suggest that OprJ is newly produced in NfxB mutants of P. aeruginosa and is involved in fluoroquinolone resistance specific to NfxB, and it appears that the MAb to OprJ should aid in detection of the NfxB mutation in P. aeruginosa.