QRDR mutations in fluoroquinolon-resistant Pseudomonas aeruginosa and its relationship with the usage of antibiotics in nosocomial pneumonia.

Objective To investigate the mutations of quinolone resistance determinational region(QRDR) in fluoroquinolon-resistant Pseudomonas aeruginosa strains isolated from patients with nosocomial pneumonia. Methods Eight-four Pseudomonas aeruginosa strains isolated from patients with nosocomial pneumonia in Xinhua Hospital during January 2006 to December 2007,from whom fluoroquinolon-resistant resisitant (case) and fluoroquinolon-susceptible (control) Pseudomona aeruginosa were identified. The mutation of QRDR was tested by restriction fragment length polymorphism (RFLP) and gene sequencing. The relationship between QRDR mutations and clinical prescription was analyzed. Results Mutation in QRDR was found in 42 isolates among the 50 fluoroquinlon-resisitant isolates(84.0%),while no mutation was found in fluoroquinlon-susceptible isolates. The mutation in GyrB Ser464 was found in 34 isolates(68.0%). There was statistical difference in the usage of β-lactams between the GyrB-Ser464-mutated group and the non-GyrB-Ser464-mutated group(OR=11.3,P=0.003 and OR=3.5,P=0.023),also in the time of fluoroquinolon usage before isolated (P=0.038). Conclusions The mutation of QRDR is contributing to fluoroquindor-resisitance of Pseudomona aeruginosa,most of which lies in GyrB Ser464. Abuse of β-lactams and fluoroquinolon may be the risk factors of mutation in GyrB Ser464.