The zoonotic pathogen Leptospira interrogans mitigates environmental stress through cyclic-di-GMP-controlled biofilm production

Investigations into the growth and formation of biofilm by Leptospira biflexa at temperatures encountered during infection

The genus Leptospira comprises unique atypical spirochete bacteria that includes the etiological agent of leptospirosis, a globally important zoonosis. Biofilms are microecosystems composed of microorganisms embedded in a self-produced matrix that offers protection against hostile factors. Leptospires form biofilms in vitro, in situ in rice fields and unsanitary urban areas, and in vivo while colonizing rodent kidneys. The complex three-dimensional biofilm matrix includes secreted polymeric substances such as proteins, extracellular DNA (eDNA), and saccharides. The genus Leptospira comprises pathogenic and saprophytic species with the saprophytic L. biflexa being commonly used as a model organism for the genus. In this study, the growth and formation of biofilms by L. biflexa was investigated not just at 29 °C, but at 37 °C/5 % CO2, a temperature similar to that encountered during host infection. Planktonic free-living L. biflexa grow in HAN media at both 29 °C and 37 °C/5 % CO2, but cells grown at 37 °C/5 % CO2 are longer (18.52 μm ± 3.39) compared to those at 29 °C (13.93 μm ± 2.84). Biofilms formed at 37 °C/5 % CO2 had more biomass compared to 29 °C, as determined by crystal violet staining. Confocal microscopy determined that the protein content within the biofilm matrix was more prominent than double-stranded DNA, and featured a distinct layer attached to the solid substrate. Additionally, the model enabled effective protein extraction for proteomic comparison across different biofilm phenotypes. Results highlight an important role for proteins in biofilm matrix structure by leptospires and the identification of their specific protein components holds promise for strategies to mitigate biofilm formation.

Host population dynamics influence Leptospira spp. transmission patterns among Rattus norvegicus in Boston, Massachusetts, US

Leptospirosis (caused by pathogenic bacteria in the genus Leptospira) is prevalent worldwide but more common in tropical and subtropical regions. Transmission can occur following direct exposure to infected urine from reservoir hosts, or a urine-contaminated environment, which then can serve as an infection source for additional rats and other mammals, including humans. The brown rat, Rattus norvegicus, is an important reservoir of Leptospira spp. in urban settings. We investigated the presence of Leptospira spp. among brown rats in Boston, Massachusetts and hypothesized that rat population dynamics in this urban setting influence the transportation, persistence, and diversity of Leptospira spp. We analyzed DNA from 328 rat kidney samples collected from 17 sites in Boston over a seven-year period (2016-2022); 59 rats representing 12 of 17 sites were positive for Leptospira spp. We used 21 neutral microsatellite loci to genotype 311 rats and utilized the resulting data to investigate genetic connectivity among sampling sites. We generated whole genome sequences for 28 Leptospira spp. isolates obtained from frozen and fresh tissue from some of the 59 positive rat kidneys. When isolates were not obtained, we attempted genomic DNA capture and enrichment, which yielded 14 additional Leptospira spp. genomes from rats. We also generated an enriched Leptospira spp. genome from a 2018 human case in Boston. We found evidence of high genetic structure among rat populations that is likely influenced by major roads and/or other dispersal barriers, resulting in distinct rat population groups within the city; at certain sites these groups persisted for multiple years. We identified multiple distinct phylogenetic clades of L. interrogans among rats that were tightly linked to distinct rat populations. This pattern suggests L. interrogans persists in local rat populations and its transportation is influenced by rat population dynamics. Finally, our genomic analyses of the Leptospira spp. detected in the 2018 human leptospirosis case in Boston suggests a link to rats as the source. These findings will be useful for guiding rat control and human leptospirosis mitigation efforts in this and other similar urban settings.

Deciphering intricate associations between vigorous development and novel metabolic preferences of partial denitrification/anammox granular consortia within mainstream municipal wastewater

There is limited understanding of the granular partial denitrification/anammox (PD/A) microbiota and metabolic hierarchy specific to municipal wastewater treatment, particularly concerning the multi-mechanisms of functional differentiation and granulation tendencies under high-loading shocks. Therefore, this study utilized fragmented mature biofilm as the exclusive inoculum to rapidly establish a granular PD/A system. Following long-term feeding with municipal wastewater, PD/A process reached a total nitrogen removal efficiency of 97.7%, with anammox contributing over 93%. The dominant filamentous bacteria that supported the granular structure underwent significant changes throughout the operational period. Notably, the mature granular PD/A process demonstrated a distinct metabolic preference for recalcitrant, labile, and xenobiotic organics found in municipal wastewater. The biosynthesis of quorum sensing signaling molecules and core cofactors further enhanced the re-development and substrate metabolic adaptations of PD/A granules in real wastewater environments. This research illuminates the micro-ecological succession and metabolic heterogeneity of the granular PD/A process under mainstream loading.

Leptospira biofilms: implications for survival, transmission, and disease management

Leptospirosis is a zoonotic disease caused by Leptospira bacteria, affecting humans and a broad range of wild and domestic animals in diverse epidemiological settings (rural, urban, and wild). The disease's pathogenesis and epidemiology are complex networks not fully elucidated. Epidemiology reflects the One Health integrated approach of environment-animal-human interaction, causing severe illness in humans and animals, with consequent public health burdens. Saprophytic and pathogenic leptospires have been shown to form biofilms in vivo, in vitro, and in environmental samples. Biofilms are characterized by a polymeric matrix that confers protection against hostile environments (both inside and outside of the host), favoring bacterial survival and dissemination. Despite its significance, the role of this bacterial growth mode in leptospiral survival, transmission, and decreased antibiotic susceptibility remains poorly understood and underexplored. Even so, the literature indicates that biofilms might be correlated with lower antimicrobial susceptibility and chronicity in leptospirosis. In this minireview, we discuss the aspects of biofilm formation by Leptospira and their significance for epidemiology and therapeutic management. Understanding the current scenario provides insight into the future prospects for biofilm diagnosis, prevention, and treatment of leptospirosis.

Current antibiotics for leptospirosis: Are still effective?

Leptospirosis is a recurring zoonotic disease of global significance. Leptospirosis is curable, and antibiotics are available for its treatment. However, little is known about the effectiveness of the currently used antibiotics against different Leptospira species, serovars, and strains. This review aimed to give insight into the anti-leptospiral activities of the currently available antibiotics towards Leptospira strains and their effectiveness in treating and preventing leptospirosis. Anti-leptospiral activities from natural resources were also reviewed. The literature search was conducted using several databases. The majority of Leptospira strains were sensitive to the current antibiotics. Antibiotics can accelerate the defervescence and reduced the occurrence of leptospirosis cases, nevertheless, there is no affirmative evidence on the beneficial effects of the antibiotics compared to placebo in preventing death. Adverse reactions like Jarisch-Herxheimer reactions (JHR) in patients treated with the current antibiotics were also reported. Plants, marine actinobacteria and propolis are shown as potential sources of new anti-leptospiral compounds. Although leptospirosis can still be adequately treated with current antibiotics, continuous susceptibility testing and the development of novel antibiotics especially from natural resources are highly encouraged.

Insights into host-pathogen interaction based on the comparison of genomes of leptospira interrogans isolated from dogs, humans, and a rodent in the same epidemiological context: A one health approach

Leptospirosis is a zoonotic infectious disease that significantly impacts animal and public health. Comparative genomics can aid in understanding poorly understood aspects of leptospirosis pathogenesis, including infection mechanisms, antimicrobial resistance, and host interactions across different epidemiological scenarios. This study aimed to compare the genomes of Leptospira interrogans serogroup Icterohaemorrhagiae strains isolated from three host species in a single epidemiological scenario. Four strains of L. interrogans serogroup Icterohaemorrhagiae from naturally infected and clinically symptomatic dogs (C20, C29, C51, and C82) were processed for whole genome sequencing (WGS). These results were compared against WGS data from two other rodent and human strains. Phylogenetic and genomic similarity analyses demonstrated high identity and synteny between the strains isolated from humans, canines, and rodents. Small regions of divergence were observed, especially in the genome obtained from a rodent sample. The presence of 23 genes potentially associated with biofilm formation was notable, with the identification of missense mutations in eight genes. Considering the need to better understand the molecular basis involved in biofilm formation, it is of fundamental importance to elucidate the effect of mutations on the expression of the phenotype (biofilm) among different strains. The present findings highlight the necessity of One Health-based collaborative interventions to address the complex dynamics of leptospirosis transmission, involving both common hosts such as rodents and dogs, as well as less-recognized hosts.

Comparative genomics of Leptospira santarosai reveals genomic adaptations in bovine genital strains

Bovine genital leptospirosis (BGL) is a silent and chronic reproductive syndrome associated with reproductive failures that result in animal suffering and substantial financial losses for farmers. Important aspects of the interactions between the host and the pathogen during chronic leptospirosis have been well described in the kidney, but little is known about the genital infection mechanisms. The present study sheds light on the pathophysiology of BGL based on comparative genomic analysis of renal versus genital isolates of Leptospira santarosai genomes, an endemic species on Latin America. A significant number of genes were exclusive of the genital strains, with emphasis on genes associated with cell wall/membrane/envelope biogenesis, mobilome: prophages and transposons, and signal transduction mechanisms. Overall, these gene clusters play crucial roles in bacterial colonization and evasion of the immune response, which can reflect leptospiral tissue tropism to the genital niche. We provide new insights into the pathophysiology of an important and neglected syndrome in bovine, helping to elucidate the evolution of adaptation of leptospires in the genital tract of cows.

Ketone body oxidation and susceptibility to ethyl acetoacetate in a novel hemolytic multidrug-resistant strain Leptospira interrogans KeTo originated from sewage water

Terrestrial and aquatic environments contaminated with animal urine may contribute to the transmission of Leptospira, a causative agent of leptospirosis in humans and wild/domesticated animals. Although enormous amounts of work have been done decoding the ecophysiology, the factors governing the cell growth and virulence in Leptospires derived from environmental samples still remain elusive. Here, we show oxidation of a wide array of organic acids including acetoacetate by a new strain of Leptospira interrogans designated as KeTo, isolated from a sewage sample originating from a wildlife enclosure located at Mangalore, India. We further demonstrate the susceptibility of KeTo to ethyl ester of acetoacetate (ethyl acetoacetate, EA). A 4.7 Mbp genome of KeTo shared the highest relatedness to pathogenic L. interrogans RGAT (99.3%), followed by L. kirschneri 3522CT (91.3%) and other related species of Leptospira (80.8‒74.3%), and harbored genes encoding acetoacetyl-CoA synthetase and acetoacetate decarboxylase respectively involved in the acetoacetate utilization and acetone formation. In line with this, strain KeTo oxidized acetoacetate when supplied as a sole carbon. Aqueous EA suppressed biofilm formation (p < 0.0001) of KeTo in basal Ellinghausen-McCullough-Johnson-Harris (EMJH) medium. Similarly, significant inhibition in the growth/biofilm of Leptospira was recorded in semisolid EMJH with/without blood supplementation when exposed to volatile EA. The extent of ketone body oxidation and susceptibility to EA was found to vary with strain as evident through the analysis of L. interrogans serogroup Australis sv. Australis strain Ballico and L. interrogans serogroup Icterohaemorrhagiae sv. Lai Like strain AF61. In conclusion, our study demonstrated the ketone body metabolic ability and susceptibility to an esterified derivative of a major ketone body in the tested strains of L. interrogans. Molecular aspects governing EA-driven growth inhibition warrant further investigations to develop optimal therapeutics for leptospirosis.

Leptospira interrogans biofilm transcriptome highlights adaption to starvation and general stress while maintaining virulence

Life-threatening Leptospira interrogans navigate a dual existence: surviving in the environment and infecting mammalian hosts. Biofilm formation is presumably an important survival strategy to achieve this process. Understanding the relation between biofilm and virulence might improve our comprehension of leptospirosis epidemiology. Our study focused on elucidating Leptospira's adaptations and regulations involved in such complex microenvironments. To determine the transcriptional profile of Leptospira in biofilm, we compared the transcriptomes in late biofilms and in exponential planktonic cultures. While genes for motility, energy production, and metabolism were downregulated, those governing general stress response, defense against metal stress, and redox homeostasis showed a significant upsurge, hinting at a tailored defensive strategy against stress. Further, despite a reduced metabolic state, biofilm disruption swiftly restored metabolic activity. Crucially, bacteria in late biofilms or resulting from biofilm disruption retained virulence in an animal model. In summary, our study highlights Leptospira's adaptive equilibrium in biofilms: minimizing energy expenditure, potentially aiding in withstanding stresses while maintaining pathogenicity. These insights are important for explaining the survival strategies of Leptospira, revealing that a biofilm lifestyle may confer an advantage in maintaining virulence, an understanding essential for managing leptospirosis across both environmental and mammalian reservoirs.

Host population structure and rare dispersal events drive leptospirosis transmission patterns among Rattus norvegicus in Boston, Massachusetts, US

Leptospirosis (caused by pathogenic bacteria in the genus Leptospira ) is prevalent worldwide but more common in tropical and subtropical regions. Transmission can occur following direct exposure to infected urine from reservoir hosts, such as rats, or a urine-contaminated environment, which then can serve as an infection source for additional rats and other mammals, including humans. The brown rat, Rattus norvegicus , is an important reservoir of leptospirosis in urban settings. We investigated leptospirosis among brown rats in Boston, Massachusetts and hypothesized that rat dispersal in this urban setting influences the movement, persistence, and diversity of Leptospira . We analyzed DNA from 328 rat kidney samples collected from 17 sites in Boston over a seven-year period (2016-2022); 59 rats representing 12 of 17 sites were positive for Leptospira . We used 21 neutral microsatellite loci to genotype 311 rats and utilized the resulting data to investigate genetic connectivity among sampling sites. We generated whole genome sequences for 28 Leptospira isolates obtained from frozen and fresh tissue from some of the 59 Leptospira -positive rat kidneys. When isolates were not obtained, we attempted Leptospira genomic DNA capture and enrichment, which yielded 14 additional Leptospira genomes from rats. We also generated an enriched Leptospira genome from a 2018 human case in Boston. We found evidence of high genetic structure and limited dispersal among rat populations that is likely influenced by major roads and/or other unknown dispersal barriers, resulting in distinct rat population groups within the city; at certain sites these groups persisted for multiple years. We identified multiple distinct phylogenetic clades of L. interrogans among rats, with specific clades tightly linked to distinct rat populations. This pattern suggests L. interrogans persists in local rat populations and movement of leptospirosis in this urban rat community is driven by rat dispersal. Finally, our genomic analyses of the 2018 human leptospirosis case in Boston suggests a link to rats as the source. These findings will be useful for guiding rat control and human leptospirosis mitigation efforts in this and other urban settings.

Rainfall-driven resuspension of pathogenic Leptospira in a leptospirosis hotspot

Leptospirosis is a zoonosis caused by Leptospira bacteria present in the urine of mammals. Leptospira is able to survive in soils and can be resuspended during rain events. Here, we analyzed the pathogenic Leptospira concentration as a function of hydrological variables in a leptospirosis hot spot. A total of 226 samples were collected at the outlet of a 3 km2 watershed degraded by ungulate mammals (deer and feral pigs) and rats which are reservoirs for leptospirosis. Water samples collected at the beginning of a rain event following a dry period contained high concentrations of pathogenic Leptospira. The concentration was generally correlated with the water level and the suspended matter concentration (SMC) during the main flood event. A secondary peak of pathogenic Leptospira was sometimes detected after the main flood and in slightly turbid waters. Lastly, the pathogenic Leptospira concentration was extremely high at the end of a wet season. The pathogenic Leptospira concentrations could not be explained by a linear combination of hydrological variables (e.g. the rainfall, water level, SMC and soil moisture). However, nonlinear machine learning models of rainfall data only provided a fair fit to the observations and explained 75 % of the variance in the log10-transformed pathogenic Leptospira concentration. A comparison of identical machine learning models for the water level, SMC and pathogenic Leptospira concentration showed that the residual error in the Leptospira concentration was due to not only the small dataset but also the intrinsic characteristics of the signal. Our results support the hypothesis whereby pathogenic Leptospira survive at different depths in soils and superficial river sediments (depending on their water saturation) and are transferred to surface water during erosion. These results might help to refine leptospirosis warnings given to the local population. Future research should be focused on larger watersheds in more densely populated areas.

c-di-GMP and AHL signals-triggered chemical communication under electrical signaling disruption restores Geobacter sulfurreducens biofilm formation

Electrogenic biofilms, which have attracted considerable attention in simultaneous wastewater treatment and energy recovery in bioelectrochemical systems, are regulated by chemical communication and potassium channel-mediated electrical signaling. However, how these two communication pathways interact with each other has not been thoroughly investigated. This study first explored the roles of chemical communication, including intracellular bis-(3'-5')-cyclic dimeric guanosine monophosphate (c-di-GMP) and extracellular N-acyl-homoserine lactone (AHL)-mediated quorum sensing, in electrogenic biofilm formation through an integrated analysis of transcriptomics and metabolomics. Electrical signaling disruption inhibited the formation and electroactivity of Geobacter sulfurreducens biofilm, which was mainly ascribed to the reduction in biofilm viability and extracellular protein/polysaccharide ratio. The upregulation of expression levels of genes encoding c-di-GMP and AHL synthesis by transcriptomic analysis, and the increased secretion of N-butanoyl-L-homoserine lactone by metabolomic analysis confirmed the enhancement of chemical communication under electrical signaling disruption, thus indicating a compensatory mechanism among different signaling pathways. Furthermore, protein-protein interaction network showed the convergence of different signaling pathways, with c-di-GMP-related genes acting as central bridges. This study highlights the interaction of different signaling pathways, especially the resilience of c-di-GMP signaling to adverse external stresses, thereby laying the foundation for facilitating electrogenic biofilm formation under adverse conditions in practical applications.

Environmental Biofilms from an Urban Community in Salvador, Brazil, Shelter Previously Uncharacterized Saprophytic Leptospira

Biofilms are complex microecosystems with valuable ecological roles that can shelter a variety of microorganisms. Spirochetes from the genus Leptospira have been observed to form biofilms in vitro, in rural environments, and in the kidneys of reservoir rats. The genus Leptospira is composed of pathogenic and non-pathogenic species, and the description of new species is ongoing due to the advent of whole genome sequencing. Leptospires have increasingly been isolated from water and soil samples. To investigate the presence of Leptospira in environmental biofilms, we collected three distinct samples of biofilms formed in an urban setting with poor sanitation: Pau da Lima, in Salvador, Bahia, Brazil. All biofilm samples were negative for the presence of pathogenic leptospires via conventional PCR, but cultures containing saprophytic Leptospira were identified. Whole genomes were generated and analyzed for twenty isolates obtained from these biofilms. For species identification, we used digital DNA-DNA hybridization (dDDH) and average nucleotide identity (ANI) analysis. The obtained isolates were classified into seven presumptive species from the saprophytic S1 clade. ANI and dDDH analysis suggest that three of those seven species were new. Classical phenotypic tests confirmed the novel isolated bacteria as saprophytic Leptospira. The isolates presented typical morphology and ultrastructure according to scanning electron microscopy and formed biofilms under in vitro conditions. Our data indicate that a diversity of saprophytic Leptospira species survive in the Brazilian poorly sanitized urban environment, in a biofilm lifestyle. We believe our results contribute to a better understanding of Leptospira biology and ecology, considering biofilms as natural environmental reservoirs for leptospires.

Leptospirosis and the Environment: A Review and Future Directions

Leptospirosis is a zoonotic disease of global importance with significant morbidity and mortality. However, the disease is frequently overlooked and underdiagnosed, leading to uncertainty of the true scale and severity of the disease. A neglected tropical disease, leptospirosis disproportionately impacts disadvantaged socioeconomic communities most vulnerable to outbreaks of zoonotic disease, due to contact with infectious animals and contaminated soils and waters. With growing evidence that Leptospira survives, persists, and reproduces in the environment, this paper reviews the current understanding of the pathogen in the environment and highlights the unknowns that are most important for future study. Through a systematic Boolean review of the literature, our study finds that detailed field-based study of Leptospira prevalence, survival, and transmission in natural waters and soils is lacking from the current literature. This review identified a strong need for assessment of physical characteristics and biogeochemical processes that support long-term viability of Leptospira in the environment followed by epidemiological assessment of the transmission and movement of the same strains of Leptospira in the present wildlife and livestock as the first steps in improving our understanding of the environmental stage of the leptospirosis transmission cycle.

Genomic insights into the c-di-GMP signaling and biofilm development in the saprophytic spirochete Leptospira biflexa

C-di-GMP is a bacterial second messenger with central role in biofilm formation. Spirochete bacteria from Leptospira genus present a wide diversity, with species of medical importance and environmental species, named as saprophytic. Leptospira form biofilms in the rat's reservoir kidneys and in the environment. Here, we performed genomic analyses to identify enzymatic and effector c-di-GMP proteins in the saprophytic biofilm-forming species Leptospira biflexa serovar Patoc. We identified 40 proteins through local alignments. Amongst them, 16 proteins are potentially functional diguanylate cyclases, phosphodiesterases, or hybrid proteins. We also identified nine effectors, including PilZ proteins. Enrichment analyses suggested that c-di-GMP interacts with cAMP signaling system, CsrA system, and flagella assembly regulation during biofilm development of L. biflexa. Finally, we identified eight proteins in the pathogen Leptospira interrogans serovar Copenhageni that share high similarity with L. biflexa c-di-GMP-related proteins. This work revealed proteins related to c-di-GMP turnover and cellular response in Leptospira and their potential roles during biofilm development.

Diving into the complexity of the spirochetal endoflagellum

Spirochaetes, a phylum that includes medically important pathogens such as the causative agents of Lyme disease, syphilis, and leptospirosis, are in many ways highly unique bacteria. Their cell morphology, subcellular organization, and metabolism reveal atypical features. Spirochetal motility is also singular, dependent on the presence of periplasmic flagella or endoflagella, inserted subterminally at cell poles and not penetrating the outer membrane and elongating outside the cell as in enterobacteria. In this review we present a comprehensive comparative genomics analysis of endoflagellar systems in spirochetes, highlighting recent findings on the flagellar basal body and filament. Continued progress in understanding the function and architecture of spirochetal flagella is uncovering paradigm-shifting mechanisms of bacterial motility.

Biofilm formation in vitro by Leptospira interrogans strains isolated from naturally infected dogs and their role in antimicrobial resistance

Leptospira interrogans is a biofilm-forming pathogen, however, there are few data involving Brazilian strains isolated from dogs and their antimicrobial sensitivity in planktonic and biofilm forms. The potential for biofilm formation and antimicrobial resistance in naturally infected dogs is a fundamental approach towards disease epidemiology and the establishment of consistent prophylaxis and control measures. The objective of this study was to evaluate in vitro biofilm formation of a reference strain (L. interrogans, sv. Copenhageni L1 130 - L20) and of L. interrogans isolated from dogs (C20, C29, C51, C82), with subsequent evaluation of antimicrobial susceptibility in planktonic and biofilm forms. The semi quantification of biofilm production revealed a dynamic process of development over time, with mature biofilm formation early on the seventh day of incubation. All strains were efficient for in vitro biofilm formation and, in this form, they were considerably more resistant compared to their planktonic form, with MIC₉₀ of 1600 μg/mL for amoxicillin, 800 μg/mL for ampicillin, and >1600 μg/mL for doxycycline and ciprofloxacin. The strains studies were isolated on naturally infected dogs that might act as reservoirs and sentinels for human infections. The potential to antimicrobial resistance together with the close relation between dogs and humans indicates the need for greater actions on disease control and surveillance. Moreover, biofilm formation may contribute to the persistence of Leptospira interrogans in the host and these animals can act as chronic carriers, disseminating the agent in the environment.

Bacterial second messenger c-di-GMP: Emerging functions in stress resistance

In natural environments, bacteria constantly encounter various stressful conditions, including nutrient starvation, toxic chemicals, and oxidative stress. The ability to adapt to these adverse conditions is crucial for bacterial survival. Frequently, bacteria utilize nucleotide signaling molecules such as cyclic diguanylate (c-di-GMP) to regulate their behaviors when encounter stress conditions. c-di-GMP is a ubiquitous bacterial second messenger regulating the transition between the planktonic state and biofilm state. An essential feature of biofilms is the production of extracellular matrix that covers bacterial cells and offers a physical barrier protecting the cells from environmental assaults. Beyond that, accumulating evidences have demonstrated that changes in the environment, including stress stimuli, cause the alteration of intracellular levels of c-di-GMP in bacterial cells, which is immediately sensed by a variety of downstream effectors that induce an appropriate stress response. In this review, we summarize recent research on the role of c-di-GMP signaling in bacterial responses to diverse stress conditions.

Analysis of 1840 Equine Intraocular Fluid Samples for the Presence of Anti-Leptospira Antibodies and Leptospiral DNA and the Correlation to Ophthalmologic Findings in Terms of Equine Recurrent Uveitis (ERU)—A Retrospective Study

Simple Summary

In horses, the chronic intraocular leptospiral infection has been shown to cause equine recurrent uveitis (ERU). This inflammatory ophthalmic disease recurs for years and usually leads to blindness. Only recently it was found that biofilm formation of the leptospires in the vitreous cavity leads to uveitis recurrences and prevents effective elimination of the infection by antibiotics or by the immune system. The most effective treatment is vitrectomy (lavage of the vitreous cavity), which mechanically removes the biofilm infection. This surgery has been performed in horses for more than 30 years, and thousands of intraocular specimens have been analyzed for antibodies directed against leptospires and by PCR for leptospiral DNA. For the present study, medical records were retrospectively analyzed. Complete medical and laboratory records were available for 1800 intraocular specimens from horses treated from 2002 to 2017 (1387 specimens from ERU-eyes, 237 specimens from eyes affected with another type of uveitis, and 216 specimens from healthy eyes). In 83% of intraocular samples from ERU eyes, antibodies were detectable, and especially the detection of immunoglobulin A (IgA) seems to play an important role. In 72% of the intraocular specimens, leptospiral DNA was detectable by PCR. No antibodies were detectable in the samples from eyes with another type of uveitis or in the samples from healthy eyes. A PCR was positive in only one sample from a healthy eye. These results with a very high number of intraocular specimens demonstrate the great importance of an intraocular leptospiral infection for ERU. It can be concluded that for a reliable diagnosis of intraocular leptospiral infection or to reliably exclude an infection, multiple tests should be applied.

Abstract

In the equine clinic of the LMU in Munich, therapeutic vitrectomies have been routinely performed in horses for three decades. The vitreous samples obtained during vitrectomies were usually tested for anti-Leptospira antibodies and for more than 20 years also by PCR for leptospiral DNA. If the indication for surgery was ophthalmologically inconclusive, an aqueous humor was collected preoperatively and examined for evidence of leptospiral infection. In this study, medical records from 2002 to 2017 were analyzed. Records for 1387 eyes affected by equine recurrent uveitis (ERU) and 237 eyes affected by another type of uveitis met the inclusion criteria. A total of 216 samples from healthy eyes were used as controls. In 83% of intraocular samples from ERU eyes, antibody titers of 1:100 or higher were detectable by microscopic agglutination test (MAT). Similarly, 83% of intraocular samples had anti-Leptospira antibodies detected by ELISA. In 72% of the intraocular specimens, leptospiral DNA was detectable by PCR. No antibodies were detectable in the samples from eyes with another type of uveitis or in the samples from healthy eyes. A PCR was positive in only one sample from a healthy eye. These results with a very high number of intraocular specimens demonstrate the great importance of an intraocular leptospiral infection for ERU. It can be concluded that for a reliable diagnosis of intraocular leptospiral infection or to reliably exclude an infection multiple tests should be applied.

Biofilm formation and social interaction of Leptospira in natural and artificial environments

In the recent decades, there has been increased interest in the study on social interactions of pathogenic bacteria and biofilm-forming microbes. Leptospira is a zoonotic pathogen that causes human leptospirosis. Biofilm formation by pathogenic and saprophytic Leptospira has been documented in various biotic and abiotic environments. Biofilm supports cell growth and protects them from a variety of environmental stress. Pathogenic bacterial biofilm might increase the virulence and pathogenesis. However, research on the social behaviour and biofilm production by Leptospira is limited. This review discusses the interplay between the different species in the biofilm formation of saprophytic and pathogenic Leptospira and potential future applications.

Influence of Temperature on Biofilm Formation Mechanisms Using a Gravity-Driven Membrane (GDM) System: Insights from Microbial Community Structures and Metabolomics

A biofilm has a significant effect on water treatment processes. Currently, there is a lack of knowledge about the effect of temperature on the biofilm structure in water treatment processes. In this study, a gravity-driven membrane ultrafiltration system was operated with river feedwater at two temperatures ("low", 4 °C; "high", 25 °C) to explore the biofilm structure and transformation mechanism. The results showed that the difference in dissolved oxygen concentration might be one of the main factors regulating the structural components of the biofilm. A denser biofilm formation and reduced flux were observed at the lower temperature. The linoleic acid metabolism was significantly inhibited at low temperature, resulting in enhanced pyrimidine metabolism by Na⁺ accumulation. In addition, the biofilm at low temperature had a higher proportion of the metabolites of lipids and lipid-like molecules (11.25%), organic acids and derivatives (10.83%), nucleosides, nucleotides, and analogues (7.083%), and organoheterocyclic compounds (6.66%). These small molecules secrete more polysaccharides having C═O and O═C-O functional groups, which intensified the resistance of the biofilm. Furthermore, the upregulation pathway of pyrimidine metabolism also increased the risk of urea accumulation at low temperature. Limnohabitans, Deinococcus, Diaphorobacter, Flavobacterium, and Pseudomonas were identified as the principal microorganisms involved in this metabolic transformation.

Diverse lineages of pathogenic Leptospira species are widespread in the environment in Puerto Rico, USA

Background

Leptospirosis, caused by Leptospira bacteria, is a common zoonosis worldwide, especially in the tropics. Reservoir species and risk factors have been identified but surveys for environmental sources are rare. Furthermore, understanding of environmental Leptospira containing virulence associated genes and possibly capable of causing disease is incomplete, which may convolute leptospirosis diagnosis, prevention, and epidemiology.

Methodology/Principal findings

We collected environmental samples from 22 sites in Puerto Rico during three sampling periods over 14-months (Dec 2018-Feb 2020); 10 water and 10 soil samples were collected at each site. Samples were screened for DNA from potentially pathogenic Leptospira using the lipL32 PCR assay and positive samples were sequenced to assess genetic diversity. One urban site in San Juan was sampled three times over 14 months to assess persistence in soil; live leptospires were obtained during the last sampling period. Isolates were whole genome sequenced and LipL32 expression was assessed in vitro.

We detected pathogenic Leptospira DNA at 15/22 sites; both soil and water were positive at 5/15 sites. We recovered lipL32 sequences from 83/86 positive samples (15/15 positive sites) and secY sequences from 32/86 (10/15 sites); multiple genotypes were identified at 12 sites. These sequences revealed significant diversity across samples, including four novel lipL32 phylogenetic clades within the pathogenic P1 group. Most samples from the serially sampled site were lipL32 positive at each time point. We sequenced the genomes of six saprophytic and two pathogenic Leptospira isolates; the latter represent a novel pathogenic Leptospira species likely belonging to a new serogroup.

Conclusions/Significance

Diverse and novel pathogenic Leptospira are widespread in the environment in Puerto Rico. The disease potential of these lineages is unknown but several were consistently detected for >1 year in soil, which could contaminate water. This work increases understanding of environmental Leptospira diversity and should improve leptospirosis surveillance and diagnostics.

Formation of Biofilm by Tetragenococcus halophilus Benefited Stress Tolerance and Anti-biofilm Activity Against S. aureus and S. Typhimurium

Tetragenococcus halophilus, a halophilic lactic acid bacterium (LAB), plays an important role in the production of high-salt fermented foods. Generally, formation of biofilm benefits the fitness of cells when faced with competitive and increasingly hostile fermented environments. In this work, the biofilm-forming capacity of T. halophilus was investigated. The results showed that the optimal conditions for biofilm formation by T. halophilus were at 3–9% salt content, 0–6% ethanol content, pH 7.0, 30°C, and on the surface of stainless steel. Confocal laser scanning microscopy (CLSM) analysis presented a dense and flat biofilm with a thickness of about 24 μm, and higher amounts of live cells were located near the surface of biofilm and more dead cells located at the bottom. Proteins, polysaccharides, extracellular-DNA (eDNA), and humic-like substances were all proved to take part in biofilm formation. Higher basic surface charge, greater hydrophilicity, and lower intracellular lactate dehydrogenase (LDH) activities were detected in T. halophilus grown in biofilms. Atomic force microscopy (AFM) imaging revealed that biofilm cultures of T. halophilus had stronger surface adhesion forces than planktonic cells. Cells in biofilm exhibited higher cell viability under acid stress, ethanol stress, heat stress, and oxidative stress. In addition, T. halophilus biofilms exhibited aggregation activity and anti-biofilm activity against Staphylococcus aureus and Salmonella Typhimurium. Results presented in the study may contribute to enhancing stress tolerance of T. halophilus and utilize their antagonistic activities against foodborne pathogens during the production of fermented foods.

Infectious Uveitis in Horses and New Insights in Its Leptospiral Biofilm-Related Pathogenesis

Uveitis is a sight-threatening eye disease in equids known worldwide that leads to considerable pain and suffering. By far the most common type of uveitis in Germany and neighboring countries is classical equine recurrent uveitis (ERU), which is caused by chronic intraocular leptospiral infection and is the main cause of infectious uveitis in horses. Other infectious causes are extremely rare and are usually clinically distinguishable from ERU. ERU can be treated very effectively by vitreous cavity lavage (vitrectomy). For proper indications of this demanding surgery, it is necessary to differentiate ERU from other types of uveitis in which vitrectomy is not helpful. This can be conducted on the basis of anamnesis in combination with ophthalmologic findings and by aqueous humor examination. During vitrectomy, vitreous material is obtained. These vitreous samples have historically been used for numerous etiologic studies. In this way, a chronic intraocular leptospiral infection has been shown to be the cause of typical ERU and, among other findings, ERU has also been recognized as a biofilm infection, providing new insights into the pathogenesis of ERU and explaining some thus far unexplainable phenomena of ERU. ERU may not only have transmissible aspects to some types of uveitis in humans but may also serve as a model for a spontaneously occurring biofilm infection. Vitreous material obtained during therapeutically indicated vitrectomy can be used for further studies on in vivo biofilm formation, biofilm composition and possible therapeutic approaches.

Investigating the role of the carbon storage regulator A (CsrA) in Leptospira spp

Carbon Storage Regulator A (CsrA) is a well-characterized post-transcriptional global regulator that plays a critical role in response to environmental changes in many bacteria. CsrA has been reported to regulate several metabolic pathways, motility, biofilm formation, and virulence-associated genes. The role of csrA in Leptospira spp., which are able to survive in different environmental niches and infect a wide variety of reservoir hosts, has not been characterized. To investigate the role of csrA as a gene regulator in Leptospira, we generated a L. biflexa csrA deletion mutant (ΔcsrA) and csrA overexpressing Leptospira strains. The ΔcsrA L. biflexa displayed poor growth under starvation conditions. RNA sequencing revealed that in rich medium only a few genes, including the gene encoding the flagellar filament protein FlaB3, were differentially expressed in the ΔcsrA mutant. In contrast, 575 transcripts were differentially expressed when csrA was overexpressed in L. biflexa. Electrophoretic mobility shift assay (EMSA) confirmed the RNA-seq data in the ΔcsrA mutant, showing direct binding of recombinant CsrA to flaB3 mRNA. In the pathogen L. interrogans, we were not able to generate a csrA mutant. We therefore decided to overexpress csrA in L. interrogans. In contrast to the overexpressing strain of L. biflexa, the overexpressing L. interrogans strain had poor motility on soft agar. The overexpressing strain of L. interrogans also showed significant upregulation of the flagellin flaB1, flaB2, and flaB4. The interaction of L. interrogans rCsrA and flaB4 was confirmed by EMSA. Our results demonstrated that CsrA may function as a global regulator in Leptospira spp. under certain conditions that cause csrA overexpression. Interestingly, the mechanisms of action and gene targets of CsrA may be different between non-pathogenic and pathogenic Leptospira strains.

Huete S, Vincent AT, Sismeiro O, Legendre R, Varet H, Bussotti G, Lorioux C, Lechat P, Coppée JY, Veyrier FJ, Picardeau M, Benaroudj N. The oxidative stress response of pathogenic Leptospira is controlled by two peroxide stress regulators which putatively cooperate in controlling virulence

Pathogenic Leptospira are the causative agents of leptospirosis, the most widespread zoonotic infectious disease. Leptospirosis is a potentially severe and life-threatening emerging disease with highest burden in sub-tropical areas and impoverished populations. Mechanisms allowing pathogenic Leptospira to survive inside a host and induce acute leptospirosis are not fully understood. The ability to resist deadly oxidants produced by the host during infection is pivotal for Leptospira virulence. We have previously shown that genes encoding defenses against oxidants in L. interrogans are repressed by PerRA (encoded by LIMLP_10155), a peroxide stress regulator of the Fur family. In this study, we describe the identification and characterization of another putative PerR-like regulator (LIMLP_05620) in L. interrogans. Protein sequence and phylogenetic analyses indicated that LIMLP_05620 displayed all the canonical PerR amino acid residues and is restricted to pathogenic Leptospira clades. We therefore named this PerR-like regulator PerRB. In L. interrogans, the PerRB regulon is distinct from that of PerRA. While a perRA mutant had a greater tolerance to peroxide, inactivating perRB led to a higher tolerance to superoxide, suggesting that these two regulators have a distinct function in the adaptation of L. interrogans to oxidative stress. The concomitant inactivation of perRA and perRB resulted in a higher tolerance to both peroxide and superoxide and, unlike the single mutants, a double perRAperRB mutant was avirulent. Interestingly, this correlated with major changes in gene and non-coding RNA expression. Notably, several virulence-associated genes (clpB, ligA/B, and lvrAB) were repressed. By obtaining a double mutant in a pathogenic Leptospira strain, our study has uncovered an interplay of two PerRs in the adaptation of Leptospira to oxidative stress with a putative role in virulence and pathogenicity, most likely through the transcriptional control of a complex regulatory network.

Biomacromolecules of chitosan - Bacopa saponin based LipL32 gene delivery system for leptospirosis therapy

Leptospirosis is a severe bacterial infectious disease caused by the organisms belonging to the genus of Leptospira. The chitosan/Bacopa saponin/tripolyphosphate (CS/BS/TPP) nanoparticles conjugated with recombinant DNA vaccines were designed against Leptospirosis. Chitosan, a polysaccharide is suitable for delivery of drug, and gene due to its bio-compatible and biodegradable properties. Bacopa saponins are used for the induction of the immune response against microbial infections. The recombinant DNA vaccine construct was composed of the leptospiral outer membrane LipL32 gene tagged with EGFP and hGMCSF adjuvant in the pVAX1 mammalian expression vector along with the Cytomegalovirus (CMV) promoter. These recombinant DNA vaccine constructs was termed as pVAX1-EGFP-LipL32 and pVAX1-EGFP-hGMCSF-LipL32, and these constructs were conjugated with CS/BS/TPP nanoparticles by using the ionic gelation technique. Thus, CS/BS/TPP conjugated nanoparticle DNA vaccine was confirmed by functionality (FT-IR), crystalline nature (XRD) and surface charge (Zeta potential). The 90% encapsulation efficiency was observed in the conjugated nanoparticle DNA vaccine. In contrast, cell viability analysis validated that the synthesized DNA conjugated CS/BS/TPP nanoparticles showed low cytotoxicity up to 10 mg/mL. The results showed here are the initial establishment of DNA vaccine conjugated nanoparticles, which can be used as a potential anti-leptospiral vaccine.

Leptospira interrogans biofilm formation in Rattus norvegicus (Norway rats) natural reservoirs

Rattus norvegicus (Norway rat) is the main reservoir host of pathogenic Leptospira, the causative agent of leptospirosis, in urban environments. Pathogenic Leptospira forms biofilms in the environment, possibly contributing for bacterial survival and maintenance. Nonetheless, biofilms have not yet been studied in natural animal reservoirs presenting leptospiral renal carriage. Here, we described biofilm formation by pathogenic Leptospira inside the renal tubules of R. norvegicus naturally infected and captured in an urban slum endemic for leptospirosis. From the 65 rats carrying Leptospira in their kidneys, 24 (37%) presented biofilms inside the renal tubules. The intensity of leptospiral colonization in the renal tubules (OR: 1.00; 95% CI 1.05–1.1) and the type of occlusion pattern of the colonized renal tubules (OR: 3.46; 95% CI 1.20–9.98) were independently associated with the presence of Leptospira biofilm. Our data showed that Leptospira interrogans produce biofilms during renal chronic colonization in rat reservoirs, suggesting a possible role for leptospiral biofilms in the pathogenesis of leptospirosis and bacterial carriage in host reservoirs.

Leptospirosis is an infectious disease caused by pathogenic Leptospira bacteria. The main reservoir hosts of Leptospira are the brown rats (Rattus norvegicus), which are chronically colonized in the kidneys. Leptospires form biofilms, which are communities of microorganisms embedded in an extracellular polysaccharidic matrix. Leptospira pathogenesis in reservoir hosts is poorly understood. We captured 87 brown rats from an impoverished urban community that is endemic for leptospirosis. To investigate the biofilm in the rats’ kidneys, we co-localized leptospires and saccharides of the biofilm extracellular matrix in the renal tubules, using immunohistochemistry anti-Leptospira and carbohydrate staining, respectively. We quantified Leptospira using molecular tools and characterized the biofilm using electron microscopy. We analysed demographic data to identify variables correlated with renal carriage. We found that Leptospira infected 78 rats. From those, 65 were positive for immunohistochemistry in the kidneys and 24 (37%) were biofilm-positive. We found significant positive correlation between the intensity of colonization and the presence of biofilm in the kidneys. The intensity of colonization was also associated with the rats’ gender and age. Biofilm formation by Leptospira in the kidneys of natural reservoir rats fills a gap into the knowledge of leptospirosis pathogenesis.

In Vivo Biofilm Formation of Pathogenic Leptospira spp. in the Vitreous Humor of Horses with Recurrent Uveitis

Equine recurrent uveitis (ERU) causes painful inflammatory attacks and oftentimes blindness in the affected eyes. The disease is considered a late sequela of systemic leptospirosis. The most effective therapy is the surgical removal of the vitreous (vitrectomy), which is not only therapeutic, but provides vitreous material that can be assessed diagnostically. For example, the lipL32 gene, culturable Leptospira spp., and anti-Leptospira antibodies have all been detected in vitreous samples obtained from eyes with chronic ERU. Despite this clear evidence of leptospiral involvement, the systemic administration of antibiotics in infected horses is ineffective at resolving ERU. This syndrome of chronic recurrent inflammation, which is unresponsive to antibiotic therapy, combined with apparent bacteria evading the immune response, is consistent with a biofilm-associated infection. The purpose of this study, therefore, was to detect the in vivo biofilm formation of Leptospira spp. in vitreous samples collected during vitrectomy and examined using a Warthin-Starry silver stain and immunohistochemistry. All known steps of biofilm formation were visualized in these samples, including individual Leptospira spp., leptospiral microcolonies and dense roundish accumulations of Leptospira spp. In many instances spirochetes were surrounded by an extracellular substance. Taken together, data from the present study show that ERU is a biofilm-associated intraocular leptospiral infection, which best explains the typical clinical course.

Leptospirosis and Coinfection: Should We Be Concerned?

Pathogenic Leptospira is the causative agent of leptospirosis, an emerging zoonotic disease affecting animals and humans worldwide. The risk of host infection following interaction with environmental sources depends on the ability of Leptospira to persist, survive, and infect the new host to continue the transmission chain. Leptospira may coexist with other pathogens, thus providing a suitable condition for the development of other pathogens, resulting in multi-pathogen infection in humans. Therefore, it is important to better understand the dynamics of transmission by these pathogens. We conducted Boolean searches of several databases, including Google Scholar, PubMed, SciELO, and ScienceDirect, to identify relevant published data on Leptospira and coinfection with other pathogenic bacteria. We review the role of the host-microbiota in determining the synanthropic interaction of Leptospira sp. with other bacteria, thus creating a suitable condition for the leptospira to survive and persist successfully. We also discuss the biotic and abiotic factors that amplify the viability of Leptospira in the environment. The coinfection of leptospira with pathogenic bacteria has rarely been reported, potentially contributing to a lack of awareness. Therefore, the occurrence of leptospirosis coinfection may complicate diagnosis, long-lasting examination, and mistreatment that could lead to mortality. Identifying the presence of leptospirosis with other bacteria through metagenomic analysis could reveal possible coinfection. In conclusion, the occurrence of leptospirosis with other diseases should be of concern and may depend on the success of the transmission and severity of individual infections. Medical practitioners may misdiagnose the presence of multiple infections and should be made aware of and receive adequate training on appropriate treatment for leptospirosis patients. Physicians could undertake a more targeted approach for leptospirosis diagnosis by considering other symptoms caused by the coinfected bacteria; thus, more specific treatment could be given.

Molecular and Serological Prevalence of Leptospira spp. in Feral Pigs (Sus scrofa) and their Habitats in Alabama, USA

Leptospirosis is a widespread zoonosis and has been recognized as a re-emerging infectious disease in humans and a variety of wild and domestic animal species. In order to understand the prevalence and diversity of Leptospira spp. in feral pig populations of Alabama, we trapped 315 feral pigs in Bullock County east-central Alabama, and collected 97 environmental samples from riparian areas in Bullock County and Macon County east-central Alabama. Two previously published PCRs followed by DNA sequencing and BLASTn were performed to identify pathogenic Leptospira species in the kidney of feral pigs (3.2%, 10/315) as well as environmental samples collected from the habitats of feral pigs (2.1%, 2/97), but not in the whole blood samples (n = 276) or spleen (n = 51). An ELISA determined that 44.2% of serum samples (122/276) were antibody-positive for Leptospira. The identification of two pathogenic Leptospira species from environmental samples and the high sero-positivity in feral pigs suggests potential pathogen shedding from feral pigs to environments, and to humans and domestic animals. In order to better understand the risk to human health associated with feral swine presence, further studies are warranted to explore the interrelationship between Leptospira spp. shedding in the urine of feral pigs and bacterial culture to explore pathogenicity. Multi-locus sequencing typing (MLST) and microscopic agglutination tests (MAT) should be performed in future studies to make a definite determination of pathogenic Leptospira in feral pigs in Alabama.

Leptospira interrogans Retains Direct Virulence After Long Starvation in Water

Mostly studied as a zoonosis, leptospirosis is also an environment-borne infection and most human cases originate from soil or water contaminations. Yet, only few studies have been interested in the survival of pathogenic Leptospira in freshwater. In this study, water microcosms were designed to evaluate the survival and virulence of Leptospira spp. for 2 years. Four commercial bottled drinking waters and a non-ionized water, all previously filter-sterilized, were studied. Either one of two Leptospira interrogans strains, one Leptospira borgpetersenii strain, or a saprophytic Leptospira biflexa was inoculated in these waters under nutrient-deprived conditions. Molecular, microscopic and cultural approaches were used to study Leptospira survival. Direct virulence of the pathogens was assessed using animal challenge without re-culturing. Our results confirmed the capacity of pathogenic Leptospira to survive for more than a year in water. In addition, we showed the ability of L. interrogans in nutrient-deprived conditions to directly cause systemic infection in susceptible animals. To our knowledge, this is the first report of direct infection of a susceptible host with Leptospira following a long starvation and survival period in nutrient-deprived water. Our results also suggest that Leptospira turned into a physiological "survival" state in harsh freshwater conditions. These data are of prime importance considering that freshwater is a major source of Leptospira infections. Environmental survival and virulence of pathogenic Leptospira spp. are becoming a crucial challenge to determine the environmental risk and adopt relevant prevention and control strategies.