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

• Published in: Microorganisms (Basel) Vol. 8; no. 4; p. 580
• Main Authors: Sheng, Haiqing, Xue, Yansong, Zhao, Wei, Hovde, Carolyn J, Minnich, Scott A
• Format: Journal Article
• Language: English
• Published: Switzerland MDPI AG 17.04.2020; MDPI
• Subjects: Antibiotics; Bacteria; Binding sites; biofilm; Biofilms; Cattle; Colonization; curli; Deoxyribonucleic acid; DNA; E coli; E. coli O157; Epidemics; Epithelial cells; Escherichia coli; Fibers; invasion; Mutagenesis; Mutation; Operons; Pathogens; Phenotypes; Pili; Plasmids; Site-directed mutagenesis; Strains (organisms); Transmission electron microscopy; Transversion; United States > US; E. coli O157; cattle; curli; invasion; biofilm
• ISSN: 2076-2607; 2076-2607
• DOI: 10.3390/microorganisms8040580

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. Tn mutagenesis identified a mutation responsible for both phenotypes. The insertion mapped within the curli 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 and , 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.