A modified MacConkey agar for selective enumeration of necrotoxigenic E. coli O55 and probiotic E. coli Nissle 1917

Priority order of neonatal colonization by a probiotic or pathogenic Escherichia coli strain dictates the host response to experimental colitis

The alarming prevalence of inflammatory bowel disease (IBD) in early childhood is associated with imbalances in the microbiome, the immune response, and environmental factors. Some pathogenic Escherichia coli (E. coli) strains have been found in IBD patients, where they may influence disease progression. Therefore, the discovery of new harmful bacterial strains that have the potential to drive the inflammatory response is of great importance. In this study, we compared the immunomodulatory properties of two E. coli strains of serotype O6: the probiotic E. coli Nissle 1917 and the uropathogenic E. coli O6:K13:H1. Using the epithelial Caco-2 cell line, we investigated the different abilities of the strains to adhere to and invade epithelial cells. We confirmed the potential of E. coli Nissle 1917 to modulate the Th1 immune response in a specific manner in an in vitro setting by stimulating mouse bone marrow-derived dendritic cells (BM-DCs). In gnotobiotic in vivo experiments, we demonstrated that neonatal colonization with E. coli Nissle 1917 achieves a stable high concentration in the intestine and protects mice from the progressive effect of E. coli O6:K13:H1 in developing ulcerative colitis in an experimental model. In contrast, a single-dose treatment with E. coli Nissle 1917 is ineffective in achieving such high concentrations and does not protect against DSS-induced ulcerative colitis in mice neonatally colonized with pathobiont E. coli O6:K13:H1. Despite the stable coexistence of both E. coli strains in the intestinal environment of the mice, we demonstrated a beneficial competitive interaction between the early colonizing E. coli Nissle 1917 and the late-arriving strain O6:K13:H1, suggesting its anti-inflammatory potential for the host. This study highlights the importance of the sequence of bacterial colonization, which influences the development of the immune response in the host gut and potentially impacts future quality of life.

Secretory IgA N-glycans contribute to the protection against E. coli O55 infection of germ-free piglets

Mucosal surfaces are colonized by highly diverse commensal microbiota. Coating with secretory IgA (SIgA) promotes the survival of commensal bacteria while it inhibits the invasion by pathogens. Bacterial coating could be mediated by antigen-specific SIgA recognition, polyreactivity, and/or by the SIgA-associated glycans. In contrast to many in vitro studies, only a few reported the effect of SIgA glycans in vivo. Here, we used a germ-free antibody-free newborn piglets model to compare the protective effect of SIgA, SIgA with enzymatically removed N-glycans, Fab, and Fc containing the secretory component (Fc-SC) during oral necrotoxigenic E. coli O55 challenge. SIgA, Fab, and Fc-SC were protective, whereas removal of N-glycans from SIgA reduced SIgA-mediated protection as demonstrated by piglets' intestinal histology, clinical status, and survival. In vitro analyses indicated that deglycosylation of SIgA did not reduce agglutination of E. coli O55. These findings highlight the role of SIgA-associated N-glycans in protection. Further structural studies of SIgA-associated glycans would lead to the identification of those involved in the species-specific inhibition of attachment to corresponding epithelial cells.

Colonization of Germ-Free Piglets with Mucinolytic and Non-Mucinolytic Bifidobacterium boum Strains Isolated from the Intestine of Wild Boar and Their Interference with Salmonella Typhimurium

Non-typhoidal Salmonella serovars are worldwide spread foodborne pathogens that cause diarrhea in humans and animals. Colonization of gnotobiotic piglet intestine with porcine indigenous mucinolytic Bifidobacterium boum RP36 strain and non-mucinolytic strain RP37 and their interference with Salmonella Typhimurium infection were compared. Bacterial interferences and impact on the host were evaluated by clinical signs of salmonellosis, bacterial translocation, goblet cell count, mRNA expression of mucin 2, villin, claudin-1, claudin-2, and occludin in the ileum and colon, and plasmatic levels of inflammatory cytokines IL-8, TNF-α, and IL-10. Both bifidobacterial strains colonized the intestine comparably. Neither RP36 nor RP37 B. boum strains effectively suppressed signs of salmonellosis. Both B. boum strains suppressed the growth of S. Typhimurium in the ileum and colon. The mucinolytic RP36 strain increased the translocation of S. Typhimurium into the blood, liver, and spleen.

Optimized dendrimer-encapsulated gold nanoparticles and enhanced carbon nanotube nanoprobes for amplified electrochemical immunoassay of E. coli in dairy product based on enzymatically induced deposition of polyaniline

A highly sensitive immunosensor was reported for Escherichia coli assay in dairy product based on electrochemical measurement of polyaniline (PAn) that was catalytically deposited by horseradish peroxidase (HRP) labels. Herein, the immunosensor was developed by using poly(amidoamine) dendrimer-encapsulated gold nanoparticles (PAMAM(Au)) as sensing platform. Importantly, the optimal HAuCl4/PAMAM ratio was investigated to design the efficient PAMAM(Au) nanocomposites. The nanocomposites were proven to not only increase the amount of immobilized capture antibody (cAb), but also accelerate the electron transfer process. Moreover, the {dAb-CNT-HRP} nanoprobes were prepared by exploiting the amplification effect of multiwalled carbon nanotubes (CNTs) for loading detection antibody (dAb) and enormous HRP labels. After a sandwich immunoreaction, the quantitatively captured nanoprobes could catalyze oxidation aniline to produce electroactive PAn for electrochemical measurement. On the basis of signal amplification of the PAMAM(Au)-based immunosensor and the {dAb-CNT-HRP} nanoprobes, the proposed strategy exhibited a linear relationship between the peak current of PAn and the logarithmic value of E. coli concentration ranging from 1.0 × 10(2) to 1.0 × 10(6) cfu mL(-1) with a detection limit of 50 cfu mL(-1) (S/N=3), and the electrochemical detection of E. coli could be achieved in 3h. The electrochemical immunosensor was also used to determine E. coli in dairy product (pure fresh milk, infant milk powder, yogurt in shelf-life and expired yogurt), and the recoveries of standard additions were in the range of 96.8-108.7%. Overall, this method gave a useful protocol for E. coli assay with high sensitivity, acceptable accuracy and satisfying stability, and thus provided a powerful tool to estimate the quality of dairy product.