A Simplified Method for the Isolation of Extracellular Vesicles from Probiotic Bacteria and Their Characterization

Probiotic bacteria are normal inhabitants of a healthy human gut, conferring multiple beneficial effects on the gut and beyond. Under various disease states, the abundance and diversity of beneficial bacteria are significantly decreased, a process called dysbiosis. Among the intra- and extracellular components of probiotics, the extracellular vesicles (EVs) secreted by them have recently garnered significant attention as potential mediators of probiotics' effects on host health. Further, these nanosized particles that encapsulate a wide range of bioactive molecules (proteins, lipids, RNA, and DNA) are standing out as key factors that could mediate gut microbiota-host communication and confer ameliorating effects in experimental inflammatory, metabolic, and cardiovascular disease models. However, a standard protocol of EV isolation from probiotic bacteria, not varying from lab to lab, must be established to achieve consistency in the experimental results in these pre-clinical models. Our current study compared two commonly used methods for EV isolation from biological samples, ultracentrifugation and precipitation, to develop a standard protocol for isolating EVs from the probiotics Lactobacillus acidophilus (LA), a Gram-positive bacterium, and Escherichia coli Nissle (EcN), a Gram-negative bacterium. The ultracentrifugation method gave ~1.5-fold higher EV yield for both LA and EcN compared to the precipitation method. Further, EcN released a higher level of EVs compared to LA. EVs were quantified and characterized by nanoparticle-tracking analysis (NTA) and by measuring the specific surface biomarkers using Western blot. Here, we describe our standardized step-by-step protocol for isolating EVs from probiotic bacteria and their characterization.