A Simple In Vitro Gut Model for Studying the Interaction between Escherichia coli and the Intestinal Commensal Microbiota in Cecal Mucus

Bioinspired in vitro intestinal mucus model for 3D-dynamic culture of bacteria

The intestinal mucus is a biological barrier that supports the intestinal microbiota growth and filters molecules. To perform these functions, mucus possesses optimized microstructure and viscoelastic properties and it is steadily replenished thus flowing along the gut. The available in vitro intestinal mucus models are useful tools in investigating the microbiota-human cells interaction, and are used as matrices for bacterial culture or as static component of microfluidic devices like gut-on-chips. The aim of this work is to engineer an in vitro mucus models (I-Bac3Gel) addressing in a single system physiological viscoelastic properties (i.e., 2-200 Pa), 3D structure and suitability for dynamic bacterial culture. Homogeneously crosslinked alginate hydrogels are optimized in composition to obtain target viscoelastic and microstructural properties. Then, rheological tests are exploited to assess a priori the hydrogels capability to withstand the flow dynamic condition. We experimentally assess the suitability of I-Bac3Gels in the evolving field of microfluidics by applying a dynamic flow to a bacterial-loaded mucus model and by monitoring E. coli growth and survival. The engineered models represent a step forward in the modelling of the mucus, since they can answer to different urgent needs such as a 3D structure, bioinspired properties and compatibility with dynamic system.

Local Delivery of Streptomycin in Microcontainers Facilitates Colonization of Streptomycin-Resistant Escherichia coli in the Rat Colon

Oral antibiotic treatment is often applied in animal studies in order to allow establishment of an introduced antibiotic-resistant bacterium in the gut. Here, we compared the application of streptomycin dosed orally in microcontainers to dosage through drinking water. The selective effect on a resistant bacterial strain, as well as the effects on fecal, luminal, and mucosal microbiota composition, were investigated. Three groups of rats (n = 10 per group) were orally dosed with microcontainers daily for 3 days. One of these groups (STR-M) received streptomycin-loaded microcontainers designed for release in the distal ileum, while the other two groups (controls [CTR] and STR-W) received empty microcontainers. The STR-W group was additionally dosed with streptomycin through the drinking water. A streptomycin-resistant Escherichia coli strain was orally inoculated into all animals. Three days after inoculation, the resistant E. coli was found only in the cecum and colon of animals receiving streptomycin in microcontainers but in all intestinal compartments of animals receiving streptomycin in the drinking water. 16S rRNA amplicon sequencing revealed significant changes in the fecal microbiota of both groups of streptomycin-treated animals. Investigation of the inner colonic mucus layer by confocal laser scanning microscopy and laser capture microdissection revealed no significant effect of streptomycin treatment on the mucus-inhabiting microbiota or on E. coli encroachment into the inner mucus. Streptomycin-loaded microcontainers thus enhanced proliferation of an introduced streptomycin-resistant E. coli in the cecum and colon without affecting the small intestine environment. While improvements of the drug delivery system are needed to facilitate optimal local concentration and release of streptomycin, the application of microcontainers provides new prospects for antibiotic treatment.

IMPORTANCE Delivery of antibiotics in microcontainer devices designed for release at specific sites of the gut represents a novel approach which might reduce the amount of antibiotic needed to obtain a local selective effect. We propose that the application of microcontainers may have the potential to open novel opportunities for antibiotic treatment of humans and animals with fewer side effects on nontarget bacterial populations. In the current study, we therefore elucidated the effects of streptomycin, delivered in microcontainers coated with pH-sensitive lids, on the selective effect on a resistant bacterium, as well as on the surrounding intestinal microbiota in rats.

E. coli enhance colonization resistance against Salmonella Typhimurium by competing for galactitol, a context-dependent limiting carbon source

The composition of intrinsic microbial communities determines if invading pathogens will find a suitable niche for colonization and cause infection or be eliminated. Here, we investigate how commensal E. coli mediate colonization resistance (CR) against Salmonella Typhimurium (S. Tm). Using synthetic bacterial communities, we show that the capacity of E. coli Mt1B1 to block S. Tm colonization depends on the microbial context. In an infection-permissive context, E. coli utilized a high diversity of carbon sources and was unable to block S. Tm invasion. In mice that were stably colonized by twelve phylogenetically diverse murine gut bacteria (OMM¹²), establishing a protective context, E. coli depleted galactitol, a substrate otherwise fueling S. Tm colonization. Here, Lachnospiraceae, capable of consuming C5 and C6 sugars, critically contributed to CR. We propose that E. coli provides CR by depleting a limited carbon source when in a microbial community adept at removing simple sugars from the intestine.

The Release of Norepinephrine in C57BL/6J Mice Treated with 6-Hydroxydopamine (6-OHDA) is Associated with Translocations in Enteric Escherichia coli via the QseC Histidine Kinase Receptor

Background

We aimed to investigate the effects of norepinephrine (NE) released from endogenous stores on bacterial translocation of Escherichia coli in mice by administration of 6-hydroxydopamine (6-OHDA), which selectively destroys noradrenergic nerve terminals.

Material/Methods

E. coli strain BW25113 and its derivatives (BW25113ΔqseC and BW25113ΔqseC pQseC) were used in this study. The serum concentrations of endotoxin were analyzed. The strains BW25113, BW25113ΔqseC, and BW25113ΔqseC pQseC were detected respectively in tissue specimens harvested from mice treated with 6-OHDA.

Results

Mice treated with BW25113ΔqseC showed reduced levels of bacterial translocation following administration of 6-OHDA compared with mice treated with BW25113. The defect of E. coli QseC receptor caused the norepinephrine-QseC signal chain to be interrupted, and the invasiveness and penetrating power of the bacteria on the intestinal mucosa was weakened, eventually leading to a significant decrease in the incidence of bacterial translocation.

Conclusions

NE modulates the interaction of enteric bacterial pathogens with their hosts via QseC. The blockade of the QseC receptor-mediated effects may be useful to attenuate bacterial translocation.

Generation of 13C-Labeled MUC5AC Mucin Oligosaccharides for Stable Isotope Probing of Host-Associated Microbial Communities

Stable isotope probing (SIP) has emerged as a powerful tool to address key questions about microbiota structure and function. To date, diverse isotopically labeled substrates have been used to characterize in situ growth activity of specific bacterial taxa and have revealed the flux of bioavailable substrates through microbial communities associated with health and disease. A major limitation to the growth of the field is the dearth of biologically relevant "heavy" labeled substrates. Mucin glycoproteins, for example, comprise an abundant source of carbon in the gut, oral cavity, respiratory tract, and other mucosal surfaces but are not commercially available. Here, we describe a method to incorporate a ¹³C-labeled monosaccharide into MUC5AC, a predominant mucin in both gastrointestinal and airway environments. Using the lung adenocarcinoma cell line, Calu-3, polarized cell cultures grown in ¹³C-labeled d-glucose resulted in liberal mucin production on the apical surface. Mucins were isolated by size-exclusion chromatography, and O-linked glycans were released by β-elimination, permethylated, and analyzed by electrospray ionization tandem mass spectrometry (ESI-MS/MS) and matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) techniques. We demonstrate a 98.7% incorporation of ¹³C in the heterogeneous O-linked oligosaccharides that make up >80% of mucin dry weight. These "heavy" labeled glycoproteins represent a valuable tool for probing in vivo activity of host-associated bacterial communities and their interactions with the mucosal barrier. The continued expansion of labeled substrates for use in SIP will eventually allow bacterial taxa that degrade host compounds to be identified, with long-term potential for improved health and disease management.