Significance: Human gut microbes form a complex community with vast biosynthetic potential. Microbial products and metabolites released in the gut impact human health and disease. However, defining causative relationships between specific bacterial products and disease initiation and progression remains an immense challenge. This study advances understanding of the functional capacity of the gut microbiota by determining the presence, concentration, and spatial and temporal variability of two enterotoxic metabolites produced by the gut-resident Klebsiella oxytoca . We present a detailed mode of action for the cytotoxins and recapitulate their functionalities in disease models in vivo. The findings provide distinct molecular mechanisms for the enterotoxicity of the metabolites allowing them to act in tandem to damage the intestinal epithelium and cause colitis.

Humanized mouse models have been widely used in virology, immunology, and oncology in the last decade. With advances in the generation of knockout mouse strains, it is now possible to generate animals in which human immune cells or human tissue can be engrafted. These models have been used for the study of human infectious diseases, cancers, and autoimmune diseases. In recent years, there has been an increase in the use of humanized mice to model human-specific viral infections. A human immune system in these models is crucial to understand the pathogenesis observed in human patients, which allows for better treatment design and vaccine development. Recent advances in our knowledge about viral pathogenicity and immune response using NSG and NRG mice are reviewed in this paper.

Non-ribosomal peptides are one class of bacterial metabolites formed by gut microbiota. Intestinal resident Klebsiella oxytoca produces two pyrrolobenzodiazepines, tilivalline and tilimycin, via the same nonribosomal biosynthesis platform. These molecules cause human disease by genotoxic and tubulin inhibitory activities resulting in apoptosis of the intestinal epithelium, loss of barrier integrity and ultimately colitis. Here we report a fast, reliable, HPLC-HR-ESMS2 method for quantifying simultaneously the bacterial enterotoxins tilimycin and tilivalline in complex biological matrices. We synthesized and applied stable isotopically labeled internal standards for precise quantification of the metabolites. Sample preparation was optimized using clinical and laboratory specimens including serum, colonic fluid and stool. The developed method overcame the disadvantage of low selectivity by applying high resolution mass spectrometry in MS2 mode. High sensitivity and low interference from matrices were achieved and validated. We show that the approach is suitable for detection and quantification of the enterotoxic metabolites produced in vivo, in infected human or animal hosts, and in bacterial culture in vitro.

Different humanized mouse models have been developed to study human diseases such as autoimmune illnesses, cancer and viral infections. These models are based on the use of immunodeficient mouse strains that are transplanted with human tissues or human immune cells. Among the latter, mice transplanted with hematopoietic stem cells have been widely used to study human infectious diseases. However, mouse models built upon the transplantation of donor-specific mature immune cells are still under development, especially in the field of viral infections. These models can retain the unique immune memory of the donor, making them suitable for the study of correlates of protection upon natural infection or vaccination. Here, we will review some of these models and how they have been applied to virology research. Moreover, the future applications and the potential of these models to design therapies against human viral infections are discussed.