Tobias Joshua, Von Mentzer Astrid, Loayza Frykberg Patricia, Aslett Martin, Page Andrew J, Sjöling Åsa, Svennerholm Ann-Mari
Department of Microbiology and Immunology, Institute of Biomedicine, University of Gothenburg, S-40530, Göteborg, Sweden.
Pathogen Genomics, Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1SA, United Kingdom.
PLoS One. 2016 Apr 7;11(4):e0152899. doi: 10.1371/journal.pone.0152899. eCollection 2016.
Enterotoxigenic Escherichia coli (ETEC), one of the most common reasons of diarrhea among infants and children in developing countries, causes disease by expression of either or both of the enterotoxins heat-labile (LT) and heat-stable (ST; divided into human-type [STh] and porcine-type [STp] variants), and colonization factors (CFs) among which CS6 is one of the most prevalent ETEC CFs. In this study we show that ETEC isolates expressing CS6+STh have higher copy numbers of the cssABCD operon encoding CS6 than those expressing CS6+STp. Long term cultivation of up to ten over-night passages of ETEC isolates harboring CS6+STh (n = 10) or CS6+STp (n = 15) showed instability of phenotypic expression of CS6 in a majority of the CS6+STp isolates, whereas most of the CS6+STh isolates retained CS6 expression. The observed instability was a correlated with loss of genes cssA and cssD as examined by PCR. Mobilization of the CS6 plasmid from an unstable CS6+STp isolate into a laboratory E. coli strain resulted in loss of the plasmid after a single over-night passage whereas the plasmid from an CS6+STh strain was retained in the laboratory strain during 10 passages. A sequence comparison between the CS6 plasmids from a stable and an unstable ETEC isolate revealed that genes necessary for plasmid stabilization, for example pemI, pemK, stbA, stbB and parM, were not present in the unstable ETEC isolate. Our results indicate that stable retention of CS6 may in part be affected by the stability of the plasmid on which both CS6 and STp or STh are located.
产肠毒素大肠杆菌（ETEC）是发展中国家婴幼儿腹泻最常见的病因之一，通过表达热不稳定肠毒素（LT）和热稳定肠毒素（ST，分为人型[STh]和猪型[STp]变体）中的一种或两种以及定植因子（CFs）致病，其中CS6是最常见的ETEC CFs之一。在本研究中，我们发现表达CS6+STh的ETEC分离株中，编码CS6的cssABCD操纵子拷贝数高于表达CS6+STp的分离株。对携带CS6+STh（n = 10）或CS6+STp（n = 15）的ETEC分离株进行长达十代过夜培养后发现，大多数CS6+STp分离株中CS6的表型表达不稳定，而大多数CS6+STh分离株仍保留CS6表达。通过PCR检测发现，观察到的不稳定性与cssA和cssD基因的缺失相关。将不稳定的CS6+STp分离株中的CS6质粒转移到实验室大肠杆菌菌株中，过夜传代一次后质粒丢失，而CS6+STh菌株的质粒在实验室菌株中传代10次后仍保留。稳定和不稳定ETEC分离株的CS6质粒序列比较显示，不稳定ETEC分离株中不存在质粒稳定所需的基因，例如pemI、pemK、stbA、stbB和parM。我们的结果表明，CS6的稳定保留可能部分受CS6和STp或STh所在质粒稳定性的影响。
