Application of microcontainers for delivery of probiotics and antibiotics to the gut environment

Anders Meyer Torp

Research output: Book/ReportPh.D. thesis

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Abstract

The gut microbiota comprises a diverse range of microbial species with great implications on the host metabolism, health, and disease. Beneficial gut microbes, termed probiotics, have been exploited for their health-promoting abilities including treatment of diarrhea, gut infections, inflammatory bowel diseases (IBD), and other gut-associated health conditions. However, processing, storage, and oral administration of probiotics have shown to affect cell viability and gut engraftment ability, which are important factors that influences the probiotic effects. Commercial probiotics are usually desiccated to improve handling and storage stability. However, this often affects viability greatly as well as the harsh conditions encountered in the gastrointestinal tract experienced by unprotected microbes. To increase probiotic survival, several procedures have been developed for processing and delivery including optimized drying methods and protective delivery systems. A novel advanced delivery system, which is based on micrometer-sized devices called microcontainers, has been shown to enhance the bioavailability of drugs delivered to the gut. Microcontainers provide a unidirectional release in the mucus layer and targeted local release in the gut, the latter being dependent on the coating polymer.

This PhD project aimed to investigate the potential of the microcontainer delivery system to enhance in vivo gut colonization of orally delivered probiotics.

Initially, the colonization ability of two spray-dried isogenic Lactobacillus rhamnosus GG (LGG) strains administered simultaneously in capsules to rats, one in microcontainers and one unprotected, was assessed (Chapter I). Quantification of the colony-forming units (CFU) of the two isogenic strains in fecal material showed no significant difference in the initial colonization potential or prolonged colonization of bacteria delivered with or without microcontainers. A colon-targeting coating consisting of cross-linked chitosan and genipin, developed by a MIMIO PhD fellow, was tested for specific delivery of LGG to the colon of rats (Chapter II). Local delivery of viable LGG in the cecum and colon mediated by chitosan-genipin-coated microcontainers was verified by CFU counting. Next, local delivery of bacteria indigenous to the colon was planned to assess their colon-colonization ability using chitosan-genipin-coated microcontainers. For this, Escherichia coli Nissle was chosen and a freeze-drying method was implemented and optimized for the bacterium (Chapter III). However, the freeze-dried E. coli did not tolerate microcontainer loading and coating, and the in vivo study was thus modified to include the antibiotic streptomycin in the microcontainers instead of bacteria. The E. coli was administrated as a fresh culture to rats that were dosed with streptomycin in the drinking water or in microcontainers with specific release in the cecum and colon (Chapter IV). In the microcontainer-dosed group, E. coli specifically colonized the cecum and colon whereas streptomycin in the drinking water allowed a high load of E. coli colonization throughout the intestinal system, which was assessed by CFU counting. The gut microbiota composition, determined by 16S rRNA amplicon sequencing, was significantly different in the compartments engrafted with the introduced E. coli compared to the control group that did not receive streptomycin. Following the in vivo study, a review article was composed describing the obstacles and opportunities of processing and delivery of sensitive ‘next generation’ probiotics (Chapter V).

Collectively, the research done during this PhD project indicates that the microcontainer delivery system is able to deliver live bacteria to the gut, but it does not currently provide benefits to the delivered bacteria. The delivery system is suited for targeted delivery of small amounts of antibiotics and potentially other compounds that benefit from GI protection and local release in the mucus.
Original languageEnglish
Place of PublicationKgs. Lyngby
PublisherTechnical University of Denmark
Number of pages115
Publication statusPublished - 2022

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