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Leptospira Is an Environmental Bacterium That Grows in Waterlogged Soil

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Title: Leptospira Is an Environmental Bacterium That Grows in Waterlogged Soil
Authors: Yanagihara, Yasutake Browse this author
Villanueva, Sharon Y. A. M. Browse this author
Nomura, Naoki Browse this author
Ohno, Marumi Browse this author
Sekiya, Toshiki Browse this author
Handabile, Chimuka Browse this author
Shingai, Masashi Browse this author
Higashi, Hideaki Browse this author
Yoshida, Shin-Ichi Browse this author
Masuzawa, Toshiyuki Browse this author
Gloriani, Nina G. Browse this author
Saito, Mitsumasa Browse this author
Kida, Hiroshi Browse this author →KAKEN DB
Keywords: Leptospira
waterlogged soil
survival in soil
Issue Date: Apr-2022
Publisher: American Society for Microbiology
Journal Title: Microbiology Spectrum
Volume: 10
Issue: 2
Start Page: e02157-21
Publisher DOI: 10.1128/spectrum.02157-21
Abstract: Leptospirosis is a zoonotic disease caused by infection with pathogenic leptospires. Consistent with recent studies by other groups, leptospires were isolated from 89 out of 110 (80.9%) soil or water samples from varied locations in the Philippines in our surveillance study, indicating that leptospires might have a life cycle that does not involve animal hosts. However, despite previous work, it has not been confirmed whether leptospires multiply in the soil environment under various experimental conditions. Given the fact that the case number of leptospirosis is increased after flood, we hypothesized that waterlogged soil, which mimics the postflooding environment, could be a suitable condition for growing leptospires. To verify this hypothesis, pathogenic and saprophytic leptospires were seeded in the bottles containing 2.5 times as much water as soil, and bacterial counts in the bottles were measured over time. Pathogenic and saprophytic leptospires were found to increase their number in waterlogged soil but not in water or soil alone. In addition, leptospires were reisolated from soil in closed tubes for as long as 379 days. These results indicate that leptospires are in a resting state in the soil and are able to proliferate with increased water content in the environment. This notion is strongly supported by observations that the case number of leptospirosis is significantly higher in rainy seasons and increased after flood. Therefore, we reached the following conclusion: environmental soil is a potential reservoir of leptospires. IMPORTANCE Since research on Leptospira has focused on pathogenic leptospires, which are supposed to multiply only in animal hosts, the life cycle of saprophytic leptospires has long been a mystery. This study demonstrates that both pathogenic and saprophytic leptospires multiply in the waterlogged soil, which mimics the postflooding environment. The present results potentially explain why leptospirosis frequently occurs after floods. Therefore, environmental soil is a potential reservoir of leptospires and leptospirosis is considered an environment-borne as well as a zoonotic disease. This is a significant report to reveal that leptospires multiply under environmental conditions, and this finding leads us to reconsider the ecology of leptospires.
Type: article
Appears in Collections:人獣共通感染症国際共同研究所 (International Institute for Zoonosis Control) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

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