Isolation and characterization of saprophytic and pathogenic strains of Leptospira from water sources in the Midwestern United States

Authors: HAMOND, CAMILA - US Department Of Agriculture (USDA); LECOUNT, KAREN - US Department Of Agriculture (USDA); ANDERSON, TAMMY - US Department Of Agriculture (USDA); Putz, Ellie; STUBER, TOD - US Department Of Agriculture (USDA); HICKS, JESSICA - US Department Of Agriculture (USDA); CAMP, PATRICK - US Department Of Agriculture (USDA); VAN DER LINDEN, HANS - University Of Amsterdam; Bayles, Darrell; SCHLATER, LINDA - US Department Of Agriculture (USDA); Nally, Jarlath

Submitted to: Frontiers in Water
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2024
Publication Date: 2/13/2024
Citation: Hamond, C., LeCount, K., Anderson, T., Putz, E.J., Stuber, T., Hicks, J., Camp, P., Van Der Linden, H., Bayles, D.O., Schlater, L.K., Nally, J.E. 2024. Isolation and characterization of saprophytic and pathogenic strains of Leptospira from water sources in the Midwestern United States. Frontiers in Water. 6. https://doi.org/10.3389/frwa.2024.1278088.
DOI: https://doi.org/10.3389/frwa.2024.1278088

Interpretive Summary: Animal and human leptospirosis, a global zoonotic disease, is caused by an unusual and atypical bacterium in the genus Leptospira. Domestic and wild animals can act as reservoir hosts of infection and excrete Leptospira from kidneys via urine into the environment where they can survive in suitable moist conditions. Transmission of disease to animals and humans is facilitated by direct contact with urine from infected hosts or with contaminated environmental sources. In this study, we screened 105 water samples collected from water sources in Iowa for the presence of Leptospira by culture and molecular diagnostic assays. Genome sequencing of cultures from water samples identified ten different species of saprophytes as well as three novel saprophytic species. Genome sequencing also identified two novel pathogenic species. Cumulatively, 11.4% (12/105) of water samples were positive for pathogenic Leptospira. This work emphasizes the diversity of Leptospira species present in water sources in the Midwestern United States and provides unique opportunities to explore the geographic diversity and evolution of this genus. The identification of known and novel pathogenic species circulating in local water sources highlights their consideration as diagnostic antigens, as well as the role of water sources in transmission of infection to human and animal populations.

Technical Abstract: The genus Leptospira is a diverse and unique group of bacteria comprising multiple saprophytic and pathogenic species, which survive and persist in suitable moist environments. Pathogenic species cause human and animal leptospirosis, a global and neglected zoonotic disease. Disease transmission occurs by exposure to contaminated water and moist soil environments, or by contact with domestic animals and wildlife acting as reservoir hosts that shed Leptospira directly via urine. In this study, we describe the diversity of saprophytic and pathogenic species of Leptospira circulating in water sources in the Midwestern United States. Samples were collected by volunteers in eleven counties in Iowa from water sources including puddles, sewage, creeks, ponds, lakes, and rivers during the summer of 2021. One hundred and five water samples were tested by culture for the presence of saprophytic and pathogenic species, and by lipL32 qPCR specific for the detection of pathogenic species; 82 (78.1%) were culture positive and five (4.8%) were positive by lipL32 qPCR. Genome sequencing of cultures from water samples identified ten different species of saprophytes including L. montravelensis, L. kemamanensis, L. bandrabouensis, L. bourretii, L. bouyouniensis, L. chreensis, L. ellinghausenii, L. terpstrae, L. yanagawae, and L. abararensis, as well as three novel saprophytic species. Genome sequencing also identified two novel pathogenic species. The remaining cultures comprised mixed populations of saprophytic species, as well as 6 cultures comprised of a mixture of saprophytic and pathogenic species. One of these mixed cultures was enriched to select for a clonal isolate of pathogenic Leptospira, strain WS101.C1, which was classified as L. interrogans serogroup Djasiman serovar Djasiman. Cumulatively, 11.4% (12/105) of water samples were positive for pathogenic Leptospira. This work emphasizes the diversity of Leptospira species present in water sources in the midwestern U.S. and provides unique opportunities to explore the geographic diversity and evolution of this genus. The identification of known and novel pathogenic species circulating in local water sources highlights their consideration as diagnostic antigens, as well as the role of water sources in transmission of infection to human and animal populations. Integrating knowledge on human, animal, and environmental health is essential to control and predict risk for zoonotic diseases.