Typing of Shigella flexneri 4c isolates in Zhejiang province by pulsed field gel electrophoresis

Objective The present study was conducted to gain insight into the molecular epidemiological characteristics of Shigella flexneri 4c isolates in Zhejiang province and their drug resistance spectrum and provide data for the development of specific and effective measures of prevention and treatment on the basis of their types. Methods A total of 60 Shigella flexneri 4c isolates in Zhejiang province were identified and classified in accordance with the state criteria (GB 16002-1995). The disk-diffusion method (Kirby-Bauer) was used to test their susceptibility to 13 antibiotics. Homology analysis was performed through pulsed field gel electrophoresis(PFGE) with reference to the protocols set by American CDC PulseNet USA. Results A total of 60 Shigella flexneri 4c isolates were all of multi-drug resistance. Analysis showed that these isolates were 100% resistant to rifampicin and erythromycin, more than 96.2% resistant to nalidixic acid, ampicillin and doxycycline. The isolates were most susceptible to amikacin and gentamicin(86.5%). 24 PFGE patterns were identified in the 60 Shigella flexneri 4c isolates, where 36 isolates belong to pattern 1(60.0%), 2 isolates to pattern 2(3.3%) and each of the remaining 22 isolates to an independent pattern (1.7% respectively). All the isolates from outbreaks were homologous and belong to pattern 1. Conclusion Shigella flexneri 4c is a new serotype identified in 2004 in Zhejiang province. There are 60% isolates that belong to PFGE pattern 1 which contributes to an apparently epidemiological predominance and is prone to cause outbreaks. The Shigella flexneri 4c presents a serious multidrug resistance (MDR) in Zhejiang province, which may be associated with the rapid increase in and dispersing of patients infected by Shigella flexneri 4c. This condition should be taken seriously by the authorities concerned and clinical medical personnel.