Escherichia coli O157:H7 Curli Fimbriae Promotes Biofilm Formation, Epithelial Cell Invasion, and Persistence in Cattle

• DOI: 10.3390/microorganisms8040580
• Publication Date: 2020-04-21T07:23:06Z
• Authors: Haiqing Sheng; Yansong Xue; Wei Zhao; Carolyn J. Hovde; Scott A. Minnich
• Keywords: 0301 basic medicine; 2. Zero hunger; QH301-705.5; curli; invasion; biofilm; Article; 3. Good health; 03 medical and health sciences; <i>E. coli</i> O157; cattle; Biology (General)

Escherichia coli O157:H7 (O157) is noninvasive and a weak biofilm producer; however, a subset of O157 are exceptions. O157 ATCC 43895 forms biofilms and invades epithelial cells. Tn5 mutagenesis identified a mutation responsible for both phenotypes. The insertion mapped within the curli csgB fimbriae locus. Screening of O157 strains for biofilm formation and cell invasion identified a bovine and a clinical isolate with those characteristics. A single base pair A to T transversion, intergenic to the curli divergent operons csgDEFG and csgBAC, was present only in biofilm-producing and invasive strains. Using site-directed mutagenesis, this single base change was introduced into two curli-negative/noninvasive O157 strains and modified strains to form biofilms, produce curli, and gain invasive capability. Transmission electron microscopy (EM) and immuno-EM confirmed curli fibers. EM of bovine epithelial cells (MAC-T) co-cultured with curli-expressing O157 showed intracellular bacteria. The role of curli in O157 persistence in cattle was examined by challenging cattle with curli-positive and -negative O157 and comparing carriage. The duration of bovine colonization with the O157 curli-negative mutant was shorter than its curli-positive isogenic parent. These findings definitively demonstrate that a single base pair stably confers biofilm formation, epithelial cell invasion, and persistence in cattle.