Serotypes and extended-spectrum β-lactamase types of clinical isolates of Shigella spp. from the Zhejiang province of China.

To understand the distribution of the serotypes of Shigella spp. and to investigate the drug-resistant genes of extended-spectrum β-lactamases (ESBLs) in Shigella in Zhejiang province, we have collected clinically isolated Shigella isolates from 2 hospitals in Zhejiang province during August to December of 2006. There are 11 Shigella flexneri and 13 Shigella sonnei isolates, respectively. Among the 11 S. flexneri, 9 are serotype F4 and the remaining 2 are F1a and F2a. Antimicrobial susceptibility tests revealed that 20.8% of the isolates were resistant to cefotaxime and 20.8% of the isolates were intermediate to cefotaxime. Isoelectric focusing demonstrated that the ESBL-positive isolates and their transconjugants produce a single β-lactamase with a pI of 7.9 or 9.0. DNA sequence analysis demonstrated that they harbor either CTX-M-14 or CTX-M-15 gene. Pulsed-field gel electrophoresis analysis showed that 9 F4 S. flexneri isolates belong to the same clone and 13 S. sonnei isolates from different regions in Zhejiang province belong to different subclones of the same clone. In summary, resistance and reduced susceptibility to β-lactam antibiotics were mainly caused by the production of CTX-M-type ESBLs. This is the first report of CTX-M-15-type ESBLs in S. sonnei in China.