A Molecular Fingerprint Analysis of Shigella flexneri 1b in Bacillary Dysentery Outbreaks in a Nursing Home in Lungchi Township, Tainan County Introduction

Tseng SH

2004 Vol.20 NO.4

Correspondence Author:


Bacillary dysentery is both a common and important public health issue. Bacillary dysentery outbreaks caused by certain specific serotypes of Shigella spp., primarily Shigella flexneri, are frequently reported in nursing homes, homes for the mentally retarded, and rehabilitation institutions. Two bacillary dysentery outbreaks were reported in a nursing home in Lungchi Township of Tainan County from August through December 2003. The present study conducted a molecular fingerprint analysis of the 13 Shigella flexneri 1b strains isolated in the outbreaks using drug resistance testing, pulsed-field gel electrophoresis (PFGE), and enterobacterial repetitive intergenic consensus-PCR (ERIC-PCR) methods. Results show that, in drug resistance tests, two types of antibiogram were noted. Eleven strains were of type I. They were resistant to ampicillin and chloramphenical, and susceptible to cefotaxime, ciprofloxacin, and sulfamethoxazole/trimethoprim. Two strains were of type II. They were resistant to ampicillin, chloramphenicol, and sulfamethoxazole/trimethoprim, susceptible to ciprofloxacin, and showed intermediate sensitivity to cefotaxime. In PFGE testing, after cleavage with restriction enzyme XbaI, a main X-type pattern appeared. From the slight differences in PFGE- patterns between strains, this X- pattern could further be divided into three subtypes. Subtype X1 had eight strains; subtype X2 had three strains; and subtype X3 had two strains. If the strains were cleavaged with restriction enzyme NotI, an N-type pattern with three subtypes appeared. Subtype N1 had 11 strains; subtype N2 had one strain; and subtype N3 had one strain. In ERIC-PCR test, five main fingerprint types appeared. Type I had two strains; type II had one strain; type III had three strains; type IV had five strains; and type V had one strain. From the findings of PFGE and ERIC-PCR, it could be concluded that the first bacillary dysentery case surnamed Wong, of the nursing home in Lungchi Township in whom Shigella flexneri 1b was isolated on August 29, should be considered an independent case; whereas the case surnamed Kuo, diagnosed at the same time could be considered the index case of the first outbreak. The suspected index case surnamed Yang of the second outbreak on December 3 showed the same PFGE or ERIC-PCR fingerprints as those of case Kuo; therefore case Yang should not be considered the index case of the second outbreak. By date of onset, case Chen with strain No. 9203471 should be considered to be the index case of the second outbreak. ERIC-PCR technique has been found to be a useful tool in rapidly screening index cases at the early stage of disease outbreaks.