Molecular epidemiology of bloodstream-associated ST131 H30-Rx subclone infection in a region with high quinolone resistance.

Bloodstream infections caused by ST131 and ST131 H30-Rx subclones have emerged worldwide. This study was carried out to evaluate the prevalence of the ST131-Rx subclone and characterize the virulence properties of the Rx isolates among the bloodstream isolates. A total of 297 non-duplicated bloodstream isolates were studied. Antibiotic susceptibilities were tested using the disc diffusion method. PCR amplification and sequencing was used to identify ST131 and H30-Rx, the virulence gene, the β-lactamase and virotype. Quinolone resistance among bacteraemic strains was 51 %, and it was 98 % among ST131 isolates. The ST131 isolates accounted for 16 % (49) of all isolates and all ST131 isolates belonged to the extraintestinal pathogenic . The proportion of H30 subclone among the ST131 isolates was 98 %, and 75 % of H30 isolates belonged to the H30-Rx subclone. The prevalence of ST131 increased from 13 to 23 % in 4 years; however, there was a decrease in the ratio of H30-Rx infections. CTX-M-15 was detected in 85 % of ST131 and all of the H30-Rx isolates. The virulence genes associated with adhesion, cell protection, iron uptake and toxins ( and ) were more common in ST131 than in non-ST131 isolates. Most of the ST131 and H30-Rx isolates were of the C virotype. All -positive isolates were in virotype C. The ST131 clone has increased rapidly among bloodstream isolates. However, a decrease in the proportion of the H30-Rx subclone in the quinolone-resistant population suggests the possibility of dissemination of other virulent and quinolone-resistant subclones in hospital settings.