Faruque Shah M, Khan Rasel, Kamruzzaman M, Yamasaki Shinji, Ahmad Q Shafi, Azim Tasnim, Nair G Balakrish, Takeda Yoshifumi, Sack David A
Molecular Genetics Laboratory, International Centre for Diarrhoeal Disease Research, Bangladesh, Dhaka-1000, Bangladesh.
Appl Environ Microbiol. 2002 Aug;68(8):3908-13. doi: 10.1128/AEM.68.8.3908-3913.2002.
Bacillary dysentery caused by Shigella species is a public health problem in developing countries including Bangladesh. Although, shigellae-contaminated food and drinks are often the source of the epidemic's spread, the possible presence of the pathogen and transmission of it through environmental waters have not been adequately examined. We analyzed surface waters collected in Dhaka, Bangladesh, for the presence of shigellae by a combination of PCR assays followed by concentration and culturing of PCR-positive samples. Analysis of 128 water samples by PCR assays for Shigella-specific virulence genes including ipaBCD, ipaH, and stx1 identified 14 (10.9%) samples which were positive for one or more of these virulence genes. Concentration of the PCR-positive samples by filtration followed by culturing identified live Shigella species in 11 of the 14 PCR-positive samples. Analysis of rRNA gene restriction patterns (ribotype) showed that the environmental isolates shared ribotypes with a collection of clinical isolates, but in contrast to the clinical isolates, 10 of the 11 environmental isolates were either negative or carried deletions in the plasmid-encoded invasion-associated genes ipaB, ipaC, and ipaD. However, all environmental Shigella isolates were positive for the chromosomal multicopy invasion-associated gene ipaH and all Shigella dysenteriae type 1 isolates were positive for the stx1 gene in addition to ipaH. This study demonstrated the presence of Shigella in the aquatic environment and dispersion of different virulence genes among these isolates which appear to constitute an environmental reservoir of Shigella-specific virulence genes. Since critical virulence genes in Shigella are carried by plasmids or mobile genetic elements, the environmental gene pool may contribute to an optimum combination of genes, causing the emergence of virulent Shigella strains which is facilitated in particular by close contact of the population with surface waters in Bangladesh.
由志贺氏菌属引起的细菌性痢疾在包括孟加拉国在内的发展中国家是一个公共卫生问题。尽管受志贺氏菌污染的食物和饮料常常是疫情传播的源头，但该病原体在环境水体中的可能存在及其传播情况尚未得到充分研究。我们通过聚合酶链反应（PCR）检测，并对PCR阳性样本进行浓缩和培养，分析了在孟加拉国达卡采集的地表水样本中志贺氏菌的存在情况。通过针对志贺氏菌特异性毒力基因（包括ipaBCD、ipaH和stx1）的PCR检测，对128份水样进行分析，结果发现14份（10.9%）样本中一种或多种这些毒力基因呈阳性。对PCR阳性样本进行过滤浓缩，随后培养，在14份PCR阳性样本中的11份中鉴定出活的志贺氏菌属。对核糖体RNA基因限制性图谱（核糖型）的分析表明，环境分离株与一组临床分离株具有相同的核糖型，但与临床分离株不同的是，11份环境分离株中的10份在质粒编码的侵袭相关基因ipaB、ipaC和ipaD中要么呈阴性，要么存在缺失。然而，所有环境志贺氏菌分离株的染色体多拷贝侵袭相关基因ipaH均为阳性，并且所有1型痢疾志贺氏菌分离株除ipaH外，stx1基因也为阳性。本研究证明了志贺氏菌在水生环境中的存在，以及这些分离株中不同毒力基因的扩散，这些分离株似乎构成了志贺氏菌特异性毒力基因的环境库。由于志贺氏菌中的关键毒力基因由质粒或可移动遗传元件携带，环境基因库可能有助于形成基因的最佳组合，导致毒性志贺氏菌菌株的出现，孟加拉国人群与地表水的密切接触尤其促进了这种情况的发生。
