Bacteriophage Transcytosis Provides a Mechanism To Cross Epithelial Cell Layers

Abstract

Bacterial viruses are among the most numerous biological entities within the human body. These viruses are found within regions of the body that have conventionally been considered sterile, including the blood, lymph, and organs. However, the primary mechanism that bacterial viruses use to bypass epithelial cell layers and access the body remains unknown. Here, we used in vitro studies to demonstrate the rapid and directional transcytosis of diverse bacteriophages across confluent cell layers originating from the gut, lung, liver, kidney, and brain. Bacteriophage transcytosis across cell layers had a significant preferential directionality for apical-to-basolateral transport, with approximately 0.1% of total bacteriophages applied being transcytosed over a 2-h period. Bacteriophages were capable of crossing the epithelial cell layer within 10 min with transport not significantly affected by the presence of bacterial endotoxins. Microscopy and cellular assays revealed that bacteriophages accessed both the vesicular and cytosolic compartments of the eukaryotic cell, with phage transcytosis suggested to traffic through the Golgi apparatus via the endomembrane system. Extrapolating from these results, we estimated that 31 billion bacteriophage particles are transcytosed across the epithelial cell layers of the gut into the average human body each day. The transcytosis of bacteriophages is a natural and ubiquitous process that provides a mechanistic explanation for the occurrence of phages within the body.

Phage therapy: What factors shape phage pharmacokinetics and bioavailability? Systematic and critical review

“…However, it is unclear how the M13 phage particle (7 × 900 nm) meets size restrictions for particles that can be uptaken by clathrin‐dependent endocytosis (less than 200 nm in diameter) . Epithelial transcytosis of phages was recently observed in vitro by Barr et al Transcytosis has been proposed as the major way of phage absorption in the gastrointestinal tract . The general ability of microorganisms to translocate from the gut to systemic circulation has been well documented, and it is determined not only by microbial size, but also by other factors for example presented molecular patterns.…”

Review article: bacteriophages in gastroenterology—from biology to clinical applications

“…Bacteria, phages and eukaryotes have co‐evolved together in a close symbiotic relationship. Although phages are viruses that infect bacteria, it has been shown that they can penetrate epithelial cell layers and spread throughout the body . It is therefore not surprising that the eukaryote host directly interacts with the phages cohabiting with its commensal bacteria .…”

Interaction of phages, bacteria, and the human immune system: Evolutionary changes in phage therapy

“…It has been demonstrated that phages cannot attach to bacteria, which do not have a specific receptor. However, these bacterial cells can become sensitive through membrane vesicle mechanisms . Phage‐resistant Bacillus subtilis becomes sensitive to the lytic phage SPP1 when co‐cultured with the sensitive strain.…”

“…A non‐specific recognition of phages also leads to other mechanisms of endocytosis by utilising vesicles in the cells. Phages are transferred to lysosomes and then inactivated …”

“…However, these bacterial cells can become sensitive through membrane vesicle mechanisms. 103 Phage-resistant Bacillus subtilis becomes sensitive to the lytic phage SPP1 when co-cultured with the sensitive strain. This phenomenon is due to a transfer of phage receptors between the cells via membrane vesicles, not via horizontal gene transfer.…”