Role of gyrA mutation and loss of OprF in the multiple antibiotic resistance phenotype of Pseudomonas aeruginosa G49

A clinical isolate of Pseudomonas aeruginosa G48, became resistant during fluoroquinolone treatment giving rise to the posttherapy isolate, G49. To determine whether mutation in gyrA gave rise to fluoroquinolone resistance, G49 was transformed with a plasmid encoding gyra (pNJR3-2); this reduced the MIC of fluoroquinolones for G49 two-fold. DNA sequencing of gyrA of G49 demonstrated a mutation at Thr-83, substituting with isoleucine. The outer membrane of G49 was shown to lack OprF, suggesting that loss of this protein may be involved in the multiple antibiotic resistance phenotype; however, when G49 was transformed with a plasmid encoding oprF (pRW5), expression of oprF was shown to have no effect upon the phenotype.