Diversity in Genetic Regulation of Bacterial Fimbriae Assembled by the Chaperone Usher Pathway

Type 1 fimbria and P pili: regulatory mechanisms of the prototypical members of the chaperone-usher fimbrial family

Adherence to both cellular and abiotic surfaces is a crucial step in the interaction of bacterial pathogens and commensals with their hosts. Bacterial surface structures known as fimbriae or pili play a fundamental role in the early colonization stages by providing specificity or tropism. Among the various fimbrial families, the chaperone-usher family has been extensively studied due to its ubiquity, diversity, and abundance. This family is named after the components that facilitate their biogenesis. Type 1 fimbria and P pilus, two chaperone-usher fimbriae associated with urinary tract infections, have been thoroughly investigated and serve as prototypes that have laid the foundations for understanding the biogenesis of this fimbrial family. Additionally, the study of the mechanisms regulating their expression has also been a subject of great interest, revealing that the regulation of the expression of the genes encoding these structures is a complex and diverse process, involving both common global regulators and those specific to each operon.

T3SS protein EsrC binds to the lacI-like operator of type 1 fimbrial operon to suppress adhesion of Edwardsiella piscicida

Type 1 fimbria, the short hair-like appendage assembled on the bacterial surface, plays a pivotal role in adhesion and invasion in Edwardsiella piscicida. The type III secretion system (T3SS), another bacterial surface appendage, facilitates E. piscicida's replication in vivo by delivering effectors into host cells. Our previous research demonstrated that E. piscicida T3SS protein EseJ inhibits adhesion and invasion of E. piscicida by suppressing type 1 fimbria. However, how EseJ suppresses type 1 fimbria remains elusive. In this study, a lacI-like operator (nt -245 to -1 of fimA) upstream of type 1 fimbrial operon in E. piscicida was identified, and EseJ inhibits type 1 fimbria through the lacI-like operator. Moreover, through DNA pull-down and electrophoretic mobility shift assay, an AraC-type T3SS regulator, EsrC, was screened and verified to bind to nt -145 to -126 and nt -50 to -1 of fimA, suppressing type 1 fimbria. EseJ is almost abolished upon the depletion of EsrC. EsrC and EseJ impede type 1 fimbria expression. Intriguingly, nutrition and microbiota-derived indole activate type 1 fimbria through downregulating T3SS, alleviating EsrC or EseJ's inhibitory effect on lacI-like operator of type 1 fimbrial operon. By this study, it is revealed that upon entering the gastrointestinal tract, rich nutrients and indole downregulate T3SS and thereof upregulate type 1 fimbria, stimulating efficient adhesion and invasion; upon being internalized into epithelium, the limit in indole and nutrition switches on T3SS and thereof switches off type 1 fimbria, facilitating effector delivery to guarantee E. piscicida's survival/replication in vivo.IMPORTANCEIn this work, we identified the lacI-like operator of type 1 fimbrial operon in E. piscicida, which was suppressed by the repressors-T3SS protein EseJ and EsrC. We unveiled that E. piscicida upregulates type 1 fimbria upon sensing rich nutrition and the microbiota-derived indole, thereof promoting the adhesion of E. piscicida. The increase of indole and nutrition promotes type 1 fimbria by downregulating T3SS. The decrease in EseJ and EsrC alleviates their suppression on type 1 fimbria, and vice versa.

Specific Detection of Uropathogenic Escherichia coli via Fourier Transform Infrared Spectroscopy Using an Optical Biosensor

Urinary tract infections (UTIs) are caused mainly by uropathogenic Escherichia coli (UPEC), accounting for both uncomplicated (75%) and complicated (65%) UTIs. Detecting UPEC in a specific, rapid, and timely manner is essential for eradication, and optical biosensors may be useful tools for detecting UPEC. Recently, biosensors have been developed for the selective detection of antigen-antibody-specific interactions. In this study, a methodology based on the principle of an optical biosensor was developed to identify specific biomolecules, such as the PapG protein, which is located at the tip of P fimbriae and promotes the interaction of UPEC with the uroepithelium of the human kidney during a UTI. For biosensor construction, recombinant PapG protein was generated and polyclonal anti-PapG antibodies were obtained. The biosensor was fabricated in silicon supports because its surface and anchor biomolecules can be modified through its various properties. The fabrication process was carried out using self-assembled monolayers (SAMs) and an immobilized bioreceptor (anti-PapG) to detect the PapG protein. Each stage of biosensor development was evaluated by Fourier transform infrared (FTIR) spectroscopy. The infrared spectra showed bands corresponding to the C-H, C=O, and amide II bonds, revealing the presence of the PapG protein. Then, the spectra of the second derivative were obtained from 1600 to 1700 cm-1 to specifically determine the interactions that occur in the secondary structures between the biological recognition element (anti-PapG antibodies) and the analyte (PapG protein) complex. The analyzed secondary structure showed β-sheets and β-turns during the detection of the PapG protein. Our data suggest that the PapG protein can be detected through an optical biosensor and that the biosensor exhibited high specificity for the detection of UPEC strains. Furthermore, these studies provide initial support for the development of more specific biosensors that can be applied in the future for the detection of clinical UPEC samples associated with ITUs.

Colonization factors of human and animal-specific enterotoxigenic Escherichia coli (ETEC)

Colonization factors (CFs) are major virulence factors of enterotoxigenic Escherichia coli (ETEC). This pathogen is among the most common causes of bacterial diarrhea in children in low- and middle-income countries, travelers, and livestock. CFs are major candidate antigens in vaccines under development as preventive measures against ETEC infections in humans and livestock. Recent molecular studies have indicated that newly identified CFs on human ETEC are closely related to animal ETEC CFs. Increased knowledge of pathogenic mechanisms, immunogenicity, regulation, and expression of ETEC CFs, as well as the possible spread of animal ETEC to humans, may facilitate the future development of ETEC vaccines for humans and animals. Here, we present an updated review of CFs in ETEC.

Comparative Transcriptome Analysis of Shiga Toxin-Producing Escherichia coli O157:H7 on Bovine Rectoanal Junction Cells and Human Colonic Epithelial Cells during Initial Adherence

Shiga toxin-producing Escherichia coli (STEC) are notorious foodborne pathogens, capable of causing severe diarrhea and life-threatening complications in humans. Cattle, acting as both primary reservoirs and asymptomatic carriers of STEC, predominantly harbor the pathogen in their rectoanal junction (RAJ), facilitating its transmission to humans through contaminated food sources. Despite the central role of cattle in STEC transmission, the molecular mechanisms governing STEC's adaptation in the RAJ of the asymptomatic reservoir host and its subsequent infection of human colonic epithelial cells, resulting in diarrhea, remain largely unexplored. This study aims to uncover these complicated dynamics by focusing on the STEC O157:H7 serotype within two distinct host environments, bovine RAJ cells and human colonic epithelial cells, during initial colonization. We employed comparative transcriptomics analysis to investigate differential gene expression profiles of STEC O157:H7 during interactions with these cell types. STEC O157:H7 was cultured either with bovine RAJ cells or the human colonic epithelial cell line CCD CoN 841 to simulate STEC-epithelial cell interactions within these two host species. High-throughput RNA sequencing revealed 829 and 1939 bacterial genes expressed in RAJ and CCD CoN 841, respectively. After gene filtering, 221 E. coli O157:H7 genes were upregulated during initial adherence to CCD CoN cells and 436 with RAJ cells. Furthermore, 22 genes were uniquely expressed with human cells and 155 genes with bovine cells. Our findings revealed distinct expression patterns of STEC O157:H7 genes involved in virulence, including adherence, metal iron homeostasis, and stress response during its initial adherence (i.e., six hours post-infection) to bovine RAJ cells, as opposed to human colonic epithelial cells. Additionally, the comparative analysis highlighted the potential role of some genes in host adaptation and tissue-specific pathogenicity. These findings shed new light on the potential mechanisms of STEC O157:H7 contributing to colonize the intestinal epithelium during the first six hours of infection, leading to survival and persistence in the bovine reservoir and causing disease in humans.

Adhesion of Escherichia coli O157:H7 during sublethal injury and resuscitation: Importance of pili and surface properties

Escherichia coli O157:H7 can recover from sublethally injured (SI) state, which causes threat of foodborne illness. Adhesion plays a key role in the carriage of pathogens in food. In this study, we investigated the adhesion ability of SI and recovered E. coli O157:H7 wildtype and its three pili-deficient mutants (curli, type 1 fimbriae, and type IV pili) on six food-related surfaces. Plate counting was used to determine adhesion population after washing and oscillating the surfaces. Spinach exhibited the stronger adhesion population of E. coli O157:H7 than the other fresh produces (p < 0.05). In addition, at least one key pili dominated adhesion on these surfaces, and curli was always included. The adhesion population and contribution of different types of pili were jointly affected by surface and physiological state. This can be attributed to high hydrophobicity and positive charge density on surface and different expression levels of csgB, fimA, fimC and ppdD in SI and recovered cells. Among glucose, mannose, maltose, fructose, lactose, and sucrose, addition of 0.5% mannose could reduce adhesion of cells at all physiological states on stainless steel. Overall, this research will provide support for controlling adhesion of SI and recovered E. coli O157:H7.