A team of University of Arizona Health Sciences researchers at the UArizona College of Medicine—Tucson found that a combination of bacterial extracts used in Europe to treat respiratory infections may offer a new way to prevent or reduce infection by SARS-CoV-2, the virus that causes COVID-19. The study, published in the Journal of Allergy and Clinical Immunology, showed that a specific combination of bacterial extracts known as OM-85 inhibited SARS-CoV-2 infection by reducing the virus’s ability to attach to lung cells. OM-85 is a bacterial lysate, a combination of molecules extracted from the cell walls of bacteria, marketed outside the U.S. under the brand name Broncho-Vaxom as a preventive treatment for upper respiratory infections in children and adults. “Current infection prevention strategies rely on vaccines that trigger our immune system to respond primarily by producing antibodies,” said senior author Dr. Donata Vercelli, professor of cellular and molecular medicine at the UArizona College of Medicine—Tucson and professor of genetics at the BIO5 Institute. “The antibodies attach to a specific part of the virus that acts like the key and prevent it from being able to attach to the lung cell receptor, which is like a lock on the outside of the lung cell. This study is unique because it is the first time researchers have targeted the receptor (the lock) with a bacterial extract and shown it protects against infection with live virus. We’re essentially removing the lock from the cell wall so there’s nothing for the virus’s key to attach to.” When SARS-CoV-2 enters the lungs, it binds to receptors including the angiotensin converting enzyme 2 receptor, known as ACE2, on the outer membranes of lung cells. A cellular enzyme changes the shape of a protein on the virus to enable SARS-CoV-2 to breach the membrane and infect the cell. When the pandemic began, Vercelli and Vadim Pivniouk, associate professor in the Department of Cellular and Molecular Medicine, along with other members of the research team, turned to data they collected in an asthma prevention study to determine whether OM-85 treatment affected the ACE2 receptor and enzyme involved in COVID-19. Vercelli collaborated with Dr. Janko Nikolich-Žugich, professor and chair of the Department of Immunobiology, and Jennifer Uhrlaub, associate research scientist. They found that pretreatment of cells with OM-85 prevented infection by SARS-CoV-2. The ability of OM-85 to prevent viral infection was found to be dependent on its ability to decrease the expression of the ACE2 receptor. “ACE2 is the critical piece that tips the scale,” said Vercelli. “Without that initial attachment … the entire infectious process is derailed and blocked.” The rationale for using bacterial extracts to prevent viral infection relates to a previous study led by Vercelli. In 2016, her team found that exposure to environmental microbial products protected Amish farm children from asthma and allergies. “Our innate immune system has evolved under environmental pressures like bacteria, but our current lifestyles often don’t give us the chance to develop this protective immunity,” Vercelli said. “Our idea is to use bacterial lysate to train our immune system to protect us from viruses, in the same way those who are regularly exposed to farm animals are protected against a multitude of bacteria and other microbes.” According to Vercelli, treatment with bacterial lysates such as OM-85 could promote a more interactive exchange between the immune system and microbes.