Heat-killed Lactobacillus acidophilus suppresses SARS-CoV-2 infection in the human intestinal epithelial cell line Caco-2
Kazuhide Takada, Quang Duy Trinh, Yoshinori Takeda, Noriko M Tsuji, Satoshi Hayakawa, Shihoko Komine-Aizawa
Frontiers in Cellular and Infection Microbiology, doi:10.3389/fcimb.2025.1556344
Background: The gastrointestinal (GI) tract is suspected to be a possible source for the systemic spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as well as a reservoir of long coronavirus disease (COVID). Thus, the mucosal epithelial tissue of the colon is a potential target for probiotics to help control SARS-CoV-2 infection. Recently, the effect of live probiotics on COVID-19 has been evaluated. However, live probiotics have certain risks, including the transmission of antibiotic-resistant genes, disturbance of gut colonization in infants, and systemic infections induced by translocation. Therefore, there is growing interest in nonviable microorganisms, particularly heat-killed probiotic bacteria, to mitigate these risks. Methods: This study evaluated the antiviral properties of heat-killed Lactobacillus acidophilus (HK-LA) in the Caco-2 cell line. Caco-2 cells were infected by SARS-CoV-2 with or without 24-hour pretreatment of HK-LA and the presence of HK-LA during infection. Results: RT-qPCR analysis showed that HK-LA treatment significantly reduced SARS-CoV-2 genome copies by approximately 30%. Similarly, flow cytometry revealed a roughly 30% decrease in SARS-CoV-2 spike-positive Caco-2 cells following HK-LA treatment. Additionally, ELISA demonstrated a significant increase in IFN-l2 secretion induced by HK-LA. Discussion: HK-LA reduces viral infection in Caco-2 cells with an increase in IFN-l2 secretion. Therefore, heat-killed lactobacilli could potentially reduce SARS-CoV-2 infection in the GI tract, suggesting a possible clinical application.
Ethics statement Ethical approval was not required for the studies on humans in accordance with the local legislation and institutional requirements because only commercially available established cell lines were used.
Author contributions
Generative AI statement The author(s) declare that no Generative AI was used in the creation of this manuscript.
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Supplementary material The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fcimb.2025. 1556344/full#supplementary-material
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doi:10.1007/s10456-023-09878-5DOI record:
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"abstract": "<jats:sec><jats:title>Background</jats:title><jats:p>The gastrointestinal (GI) tract is suspected to be a possible source for the systemic spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), as well as a reservoir of long coronavirus disease (COVID). Thus, the mucosal epithelial tissue of the colon is a potential target for probiotics to help control SARS-CoV-2 infection. Recently, the effect of live probiotics on COVID-19 has been evaluated. However, live probiotics have certain risks, including the transmission of antibiotic-resistant genes, disturbance of gut colonization in infants, and systemic infections induced by translocation. Therefore, there is growing interest in nonviable microorganisms, particularly heat-killed probiotic bacteria, to mitigate these risks.</jats:p></jats:sec><jats:sec><jats:title>Methods</jats:title><jats:p>This study evaluated the antiviral properties of heat-killed <jats:italic>Lactobacillus acidophilus</jats:italic> (HK-LA) in the Caco-2 cell line. Caco-2 cells were infected by SARS-CoV-2 with or without 24-hour pretreatment of HK-LA and the presence of HK-LA during infection.</jats:p></jats:sec><jats:sec><jats:title>Results</jats:title><jats:p>RT-qPCR analysis showed that HK-LA treatment significantly reduced SARS-CoV-2 genome copies by approximately 30%. Similarly, flow cytometry revealed a roughly 30% decrease in SARS-CoV-2 spike-positive Caco-2 cells following HK-LA treatment. Additionally, ELISA demonstrated a significant increase in IFN-λ2 secretion induced by HK-LA.</jats:p></jats:sec><jats:sec><jats:title>Discussion</jats:title><jats:p>HK-LA reduces viral infection in Caco-2 cells with an increase in IFN-λ2 secretion. Therefore, heat-killed lactobacilli could potentially reduce SARS-CoV-2 infection in the GI tract, suggesting a possible clinical application.</jats:p></jats:sec>",
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