Prevalence and characteristics of ST131 clone among unselected clinical in a Chinese university hospital.

Background: clinical sequence type 131 (ST131) has emerged as an extensively antimicrobial resistant clonal group in recent years throughout the world. The aim of this study was to investigate the prevalence and molecular characteristics of ST131 among unselected clinical isolates in a Chinese university hospital.

Methods: Seven hundred consecutive isolates were collected at a Chinese university hospital between 2014 and 2015. Isolates belonging to ST131 were identified by PCR and multilocus sequence typing (MLST), and then characterized for antibiotic resistance, CTX-M-type extended-spectrum β-lactamase genes, fluoroquinolone resistance genes, O types, phylogenetic groups, virulence factors and PFGE patterns.

Results: Overall, 83 (11.6%) isolates were identified as ST131 group. The 30 lineage accounted for 53 (63.9%) of the ST131 isolates, including 13 30-Rx and 40 30 non-Rx. The remaining 30 isolates belonged to lineage. Two O types were identified in this study: O25b (66.3%) and O16 (33.7%). Compared with O25b-B2-ST131 isolates, O16-B2-ST131 isolates harbored less virulence factors of adhesins. ST131 30 Rx isolates had significantly higher virulence score than those of other isolates. O16-B2-ST131 isolates were shown to have a lower resistance to quinolones than O25b-B2-ST131 isolates. 5 nonsynonymous mutations (GyrA S83 L, D87N, ParC S80I, E84V and ParE I529L) were strongly associated with ST131 and O25b isolates. Results of PFGE demonstrated that these isolates were classified into 68 pulsotypes and these subtypes were grouped into 23 different PFGE clusters using 70% similarity cut-off value.

Conclusions: This is the first study to reveal the prevalence and molecular characteristic of ST131 clonal group among consecutive clinical isolates in China. Our findings demonstrated that ST131 lineage accounts for a small proportion of clinical isolates in China, which included two major groups: O25b-B2-ST131 and O16-B2-ST131. Our results implies that O16-B2-ST131 subclone may be an important type of ST 131 in China, which suggests that future studies should not ignore such clone in this country.