Bloodstream infections caused by qnr-positive Enterobacteriaceae: clinical and microbiologic characteristics and outcomes.

The clinical significance of plasmid-mediated quinolone resistance determinant qnr has not been well characterized. We investigated the clinical and microbiologic characteristics and outcomes of bloodstream infections (BSIs) caused by qnr-positive Enterobacteriaceae. We prospectively collected 351 nonduplicate consecutive blood isolates of Enterobacter spp. and Klebsiella pneumoniae. qnr genes were detected by polymerase chain reaction and confirmed by sequencing. The medical records of patients were retrospectively reviewed. qnr genes were detected in a total of 26 isolates. A comparison of these 26 qnr-positive and 297 qnr-negative Enterobacteriaceae BSIs in adult patients showed that the population characteristics and clinical features of BSIs were similar between the qnr-positive and qnr-negative groups. However, patients with hematologic malignancies, solid organ transplant recipients, and BSIs caused by strains with multiple antimicrobial resistance, including extended-spectrum beta-lactamase (ESBL) resistance, were more common in the qnr-positive group. Previous antibiotic therapy and prior use of trimethoprim-sulfamethoxazole or aminoglycosides were significantly associated with BSIs caused by qnr-positive strains. In the multivariate analysis, prior use of trimethoprim-sulfamethoxazole (odds ratio [OR], 5.55; 95% confidence interval [CI], 1.47-20.94) and having an underlying disease other than solid tumor (OR, 4.06; 95% CI, 15.07) were independently associated with qnr-positive Enterobacteriaceae BSIs. There was no significant difference in 30-day mortality rates between the qnr-positive and qnr-negative groups (15.4% [4/26] versus 13.8% [41/297], P = 0.77). Although qnr determinants were significantly associated with multiple antimicrobial resistance including ESBL resistance, they did not affect clinical outcomes of BSIs.