Live biotherapeutic products: their selective inhibition of Candida albicans and the mammalian cell response in Caco-2:HT29-MTX cells

Bronwyn Smit

doi:10.25907/00769

Due to mounting antimicrobial resistance, there is a need for alternative therapeutic interventions for infectious diseases. Candida albicans is an opportunistic fungal pathogen that commonly resides as a commensal in the gut of healthy humans and is kept under control by the host’s immune system and beneficial microbiota. However, in certain cases such as in immunocompromised individuals and those undergoing chemotherapy, the fungus may overgrow, adhere to the gut epithelium and translocate into the blood stream to cause systemic candidiasis with a morbidity and mortality rate up to about 50%. Lactic acid bacteria, in particular lactobacilli, are commonly used as probiotics to support digestive health and immune function. More recently these strains have been introduced to the body as drugs for disease prevention and treatment. The term “live biotherapeutic products” (LBPs) refers to biological products that contains live organisms such as lactobacilli and are applicable to the prevention and/or treatment of a human disease or condition and are not vaccines. This project investigated the competitive interaction of the selected LBP strains against two strains of Candida albicans i.e., ATCC 10231, a strain resistant to multiple antifungal antibiotics and the SC5314, a highly virulent and invasive strain, using an improved gut epithelial cell model. This model comprised a co-culture of Caco-2 and HT29-MTX cells with characteristics that closely resemble the gut epithelium. Caco-2 cells can be differentiated in the culture medium to form a polarised cell monolayer with tight junctions and microvilli to resemble important characteristics of human intestinal mature enterocytes. The other cell line, HT-29, with methotrexate (MTX) adaptation i.e., HT29-MTX cell line, differentiates in culture media to act as mature goblet cells and secretes mucin. Using this model, we also assessed the potential of lactobacilli LBPs to inhibit the interaction of an adherent and invasive Escherichia coli (AIEC) strain with the co-culture to establish their efficacy on pathogenic bacteria as well. Results showed reduced adhesion, invasion, and translocation of both AIEC and Candida strains by all LBP strains although these effects varied among the LBP strains. When assessing the potential for using a combination of LBPs compared to isolated LBP strains, results showed that using a combination did not exert a much stronger ability to reduce the adhesion to and invasion of C. albicans to the intestinal epithelial cells than the isolated LBP strains. Microbial interactions with the human gut interface have been shown to affect immune responses, thereby affecting susceptibility to inflammatory bowel disease (IBD) and even cancer development. To assess the mammalian cell response to the LBPs and/or C. albicans, we employed RNA-seq via next generation sequencing (NGS) to investigate the transcriptomes of intestinal epithelial cells in response to their interaction with LBPs and Candida. The results showed down-regulation of pro-inflammatory genes and up-regulation of anti-inflammatory genes in response to LBPs. Some of the LBP strains showed potential to restore a compromised epithelial barrier that has been subjected to damage, through the ability to variably upregulate certain tight junction (TJ) proteins that are important for structural maintenance of the gut barrier. These results demonstrate the potential of these LBPs to act as therapeutics for IBD. The selected LBPs also downregulated certain proto-oncogenes and upregulated tumour suppressors, highlighting their potential for use as chemotherapeutics. Furthermore, the LBPs showed huge potential in the management of pathogenic infection and other gut-associated disorders. Downregulation of certain pro-inflammatory genes and upregulation of anti-inflammatory and TJ genes by these LBPs should be further explored against other intestinal pathogens involved in pathogenesis of IBD.

Live biotherapeutic products: their selective inhibition of Candida albicans and the mammalian cell response in Caco-2:HT29-MTX cells

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