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Background: Helicobacter pylori has a high infection rate, and it is possible that more than half of the world's population is infected. The route of transmission of H. pylori has not been completely elucidated yet. The coccoid form of H. pylori is generally considered to be in a VBNC (viable but nonculturable) state, and this form in the environment is thought to play an important role in infection and transmission, but its stability and survivability are still unknown. Materials and methods: In order to promote its changing to coccoid form, the spiral form of H. pylori grown in a culture medium was exposed to sterile distilled water, and we investigated the bacterial cell number and the morphological changes by using fluorescence staining methods and electron microscopic observation. We also examined the dynamics of its growth ability by measuring the colony forming unit on an agar‐plate medium. Results: After exposure to sterile distilled water, the H. pylori spiral form rapidly lost its growth ability at 37°C. One day after exposure, approximately 95% of the spiral form disappeared and the proportion of the coccoid form increased. The total number of bacteria also decreased to less than half and continued to decrease over time. Epi‐microscopic and electron microscopic observations revealed that deformation of bacterial cells, collapse, and leaking out of cell contents were promoted in exposure to sterile distilled water. Conclusion: Helicobacter pylori quickly begins to transform into the coccoid form after exposure to sterile distilled water, rapidly loses its growth ability, and then lyses and dies. Water‐exposure is lethal for H. pylori and it is unlikely to survive in the VBNC state in water. [ABSTRACT FROM AUTHOR]

Background: Leptospirosis has been described as a biphasic disease consisting of hematogenous dissemination to major organs in the acute phase and asymptomatic renal colonization in the chronic phase. Several observational studies have suggested an association between leptospirosis and chronic kidney disease (CKD). We investigated the dynamics of leptospires and histopathological changes in the kidney to understand the relationship between them, and also investigated the extent of renal dysfunction in the acute and chronic phases of leptospirosis using a hamster model. Findings: Hamsters (n = 68) were subcutaneously infected with 1 × 104 cells of the Leptospira interrogans serovar Manilae strain UP-MMC-SM. A total of 53 infected hamsters developed fatal acute leptospirosis, and the remaining 15 hamsters recovered from the acute phase, 13 of which showed Leptospira colonization in the kidneys in the chronic phase. Five asymptomatic hamsters also had renal colonization in the chronic phase. Immunofluorescence staining showed that leptospires were locally distributed in the renal interstitium in the early acute phase and then spread continuously into the surrounding interstitium. The kidneys of the surviving hamsters in the chronic phase showed patchy lesions of atrophic tubules, a finding of chronic tubulointerstitial nephritis, which were substantially consistent with the distribution of leptospires in the renal interstitium. The degree of atrophic tubules in kidney sections correlated statistically with the serum creatinine level in the chronic phase (rs = 0.78, p = 0.01). Conclusion: Subcutaneous infection with pathogenic leptospires could cause acute death or chronic leptospirosis in hamsters after surviving the acute phase. We suggest that the renal distribution of leptospires during the acute phase probably affected the extent of tubular atrophy, leading to CKD. Author summary: Leptospirosis is the most widespread zoonotic disease, particularly in tropical and subtropical regions. Leptospires are transmitted to humans via contaminated urine, soil and water from carrier animals such as rodents. Human leptospirosis is mostly asymptomatic or a mild acute febrile illness, but some patients progress to Weil's disease, characterized by kidney failure, jaundice, and pulmonary hemorrhage, and some of them die. To understand pathogen-host interactions in the kidney, a major target of leptospirosis, the authors collected kidneys and blood samples from the acute to chronic phase using a subcutaneously infected hamster model to compare the renal distribution of Leptospira with histopathological findings and renal function. The results demonstrated that the increase in antibody titers in the acute phase affected the outcome in the natural course of acute leptospirosis, and that the distribution of leptospires in the kidney during the acute phase may affect the decline of renal function during the chronic phase. It is possible that leptospirosis is one of the causes of unexplained renal dysfunction in tropical and subtropical regions. [ABSTRACT FROM AUTHOR]