Blocking pathogenic Leptospira invasion with aptamer molecules targeting outer membrane LipL32 protein.

This study aimed to develop aptamers targeting LipL32, a most abundant lipoprotein in pathogenic Leptospira, to hinder bacterial invasion. The objectives were to identify high-affinity aptamers through SELEX and evaluate their specificity and inhibitory effects. SELEX was employed to generate LipL32 aptamers (L32APs) over 15 rounds of selection. L32APs' binding affinity and specificity for pathogenic Leptospira were assessed. Their ability to inhibit LipL32-ECM interaction and Leptospira invasion was investigated. Animal studies were conducted to evaluate the impact of L32AP treatment on survival rates, Leptospira colonization, and kidney damage. Three L32APs with strong binding affinity were identified. They selectively detected pathogenic Leptospira, sparing non-pathogenic strains. L32APs inhibited LipL32-ECM interaction and Leptospira invasion. In animal studies, L32AP administration significantly improved survival rates, reduced Leptospira colonies, and mitigated kidney damage compared to infection alone. This pioneering research developed functional aptamers targeting pathogenic Leptospira. The identified L32APs exhibited high affinity, pathogen selectivity, and inhibition of invasion and ECM interaction. L32AP treatment showed promising results, enhancing survival rates and reducing Leptospira colonization and kidney damage. These findings demonstrate the potential of aptamers to impede pathogenic Leptospira invasion and aid in recovery from Leptospira-induced kidney injury (190 words).

Acyldepsipeptide activated ClpP1P2 macromolecule of Leptospira, an ideal Achilles' heel to hamper the cell survival and deregulate ClpP proteolytic activity.

Antibiotic acyldepsipeptide (ADEP) targets the bacterial ClpP serine protease and can inhibit the growth of numerous bacterial species by activating/dysregulating the protease activity within the cell. The spirochete Leptospira interrogans harbors two ClpP isoforms (LepClpP1 and LepClpP2). Supplementation of ADEP in the Leptospira growth medium resulted in the inhibition of bacterial growth. The ADEP mediated activation of the LepClpP mixture was dependent on the time allowed for the self-assembly of LepClpP1 and LepClpP2. The dynamic light scattering of the LepClpP mixture in the presence of the ADEP indicated a conformational transformation of the LepClpP machinery. Serine 98, a catalytic triad residue of the LepClpP1 in the LepClpP1P2 heterocomplex, was critical for the ADEP mediated activation. The computational prototype of the LepClpP1P2 structure suggested that the hydrophobic pockets wherein the ADEPs or the physiological chaperone ClpX predominantly dock are exclusively present in the LepClpP2 heptamer. Using the ADEP as a tool, this investigation provides an insight into the molecular function of the LepClpP1P2 in a coalition with its ATPase chaperone LepClpX. The shreds of the evidence illustrated in this investigation verify that ADEP1 possesses the ability to control the LepClpP system in an unconventional approach than the other organisms.

The transcriptional response of pathogenic Leptospira to peroxide reveals new defenses against infection-related oxidative stress.

Pathogenic Leptospira spp. are the causative agents of the waterborne zoonotic disease leptospirosis. Leptospira are challenged by numerous adverse conditions, including deadly reactive oxygen species (ROS), when infecting their hosts. Withstanding ROS produced by the host innate immunity is an important strategy evolved by pathogenic Leptospira for persisting in and colonizing hosts. In L. interrogans, genes encoding defenses against ROS are repressed by the peroxide stress regulator, PerR. In this study, RNA sequencing was performed to characterize both the L. interrogans response to low and high concentrations of hydrogen peroxide and the PerR regulon. We showed that Leptospira solicit three main peroxidase machineries (catalase, cytochrome C peroxidase and peroxiredoxin) and heme to detoxify oxidants produced during peroxide stress. In addition, canonical molecular chaperones of the heat shock response and DNA repair proteins from the SOS response were required for Leptospira recovering from oxidative damage. Identification of the PerR regulon upon exposure to H2O2 allowed to define the contribution of this regulator in the oxidative stress response. This study has revealed a PerR-independent regulatory network involving other transcriptional regulators, two-component systems and sigma factors as well as non-coding RNAs that putatively orchestrate, in concert with PerR, the oxidative stress response. We have shown that PerR-regulated genes encoding a TonB-dependent transporter and a two-component system (VicKR) are involved in Leptospira tolerance to superoxide. This could represent the first defense mechanism against superoxide in L. interrogans, a bacterium lacking canonical superoxide dismutase. Our findings provide an insight into the mechanisms required by pathogenic Leptospira to overcome oxidative damage during infection-related conditions. This will participate in framing future hypothesis-driven studies to identify and decipher novel virulence mechanisms in this life-threatening pathogen.

The Effect of Environmental Stresses on lipL32 Gene Expression in Pathogenic Leptospira spp. through Real-Time PCR.

Leptospirosis is a worldwide infectious and zoonotic disease. The incidence of this disease is high in temperate regions, especially in northern Iran. The aim of this study was to investigate the effects of temperature, pH, and Phyllanthus amarus plant extract on the lipL32 gene expression in pathogenic Leptospira spp. Fifty water samples were collected. Culture and PCR technique were used to isolate and identify the bacterium and the presence of the lipL32 gene. The samples were exposed to different temperatures and pH levels for one day and the Ph. amarus plant extract at different concentrations for one and seven days. RNA was extracted, and cDNA synthesis was performed for all the samples. All cDNAs were evaluated by the real-time PCR (SYBR green) technique. Out of the 50 samples, ten samples (20%), using PCR were determined to contain the pathogenic Leptospira. Fold change of the expression of the lipL32 gene associated with stresses was as follows: temperature stress of 40°C, 35°C, and 25°C reduced the lipL32 gene expression in all three isolates, especially in the isolates type 1. The pH stress, i.e., pH values equal to 8 or 9 reduced the gene expression in three types of isolates, and pH = 6 stress increases the lipL32 gene expression in the isolates of type 1. Ph. amarus plant extract stress reduced the mentioned gene expression only in isolates of type 2. Temperature and pH stresses could lead to differences in the expression level and cause the lipL32 gene expression decrease in three pathogenic isolates. The MIC results showed anti-leptospiral effect of Ph. amarus plant extract.

Comparison of Leptospira species isolated from environmental water and soil in Japan.

Leptospira was isolated from environmental water in central Japan using selective medium comprising five antibiotics, namely sulfamethoxazole, trimethoprim, amphotericin B, fosfomycin, and 5-fluorouracil. Of 100 water samples 57 (57%) were culture-positive and 50 pure cultures were isolated. Of the 50 cultures isolated from water 48 were classified into a saprophytic clade on the basis of 16S ribosomal RNA gene sequences. However, it was previously reported that isolates from soil in Japan belonged to pathogenic, intermediate, and saprophytic clades, the current findings suggest less diversity of Leptospira species in environmental water than that in soil in Japan.

Antimicrobial Susceptibility Testing of Leptospira spp. in the Lao People's Democratic Republic Using Disk Diffusion.

Leptospirosis is a global zoonotic disease caused by pathogenic bacteria of the Leptospira genus, which are fastidious, slow-growing organisms. Antimicrobial susceptibility data are limited; traditionally, the organisms have not been culturable on solid media. The recent development of Leptospira Vanaporn Wuthiekanun (LVW) agar, which facilitates rapid growth of Leptospira spp., provides the opportunity for antimicrobial susceptibility testing. Eighty-three Leptospira spp. clinical isolates originating from patients in Laos between 2006 and 2016 were tested against six antimicrobials (azithromycin, ceftriaxone, ciprofloxacin, doxycycline, gentamicin, and penicillin G) using disk diffusion on LVW agar. Quality control was undertaken using American Type Culture Collection (ATCC) reference strains with known susceptibilities on both standard media and LVW agar. All Leptospira spp. isolates produced large zones of inhibition around each of the six antimicrobials. All zones were greater than 25 mm: gentamicin produced the smallest zones (median 35 mm; interquartile range 30 mm-37 mm) and azithromycin produced the largest zones (median 85 mm; interquartile range 85 mm-85 mm). Zones produced by non-leptospiral ATCC reference strains on LVW agar were within 2 mm of accepted strain-specific quality control range on standard media. Antimicrobial activity on LVW agar appears to be similar to that on standard media. As there are no published susceptibility guidelines for the Leptospira genus, zone interpretation was subjective. Leptospira Vanaporn Wuthiekanun agar enabled antimicrobial susceptibility testing of multiple Leptospira isolates on solid media; the large zone sizes observed suggest that resistance has not emerged to these six antimicrobials in Lao Leptospira spp.

Pharmacokinetics of enrofloxacin HCl-2H2 O (ENRO-C), PK/PD, and Monte Carlo modeling vs. Leptospira spp. in cows.

The pharmacokinetics, PK/PD ratios, and Monte Carlo modeling of enrofloxacin HCl-2H2 O (Enro-C) and its reference preparation (Enro-R) were determined in cows. Fifty-four Jersey cows were randomly assigned to six groups receiving a single IM dose of 10, 15, or 20 mg/kg of Enro-C (Enro-C10 , Enro-C15 , Enro-C20 ) or Enro-R. Serial serum samples were collected and enrofloxacin concentrations quantified. A composite set of minimum inhibitory concentrations (MIC) of Leptospira spp. was utilized to calculate PK/PD ratios: maximum serum concentration/MIC (Cmax /MIC90 ) and area under the serum vs. time concentration of enrofloxacin/MIC (AUC0-24 /MIC90 ). Monte Carlo simulations targeted Cmax /MIC = 10 and AUC0-24 /MIC = 125. Mean Cmax obtained were 6.17 and 2.46 µg/ml; 8.75 and 3.54 µg/ml; and 13.89 and 4.25 µg/ml, respectively for Enro-C and Enro-R. Cmax /MIC90 ratios were 6.17 and 2.46, 8.75 and 3.54, and 13.89 and 4.25 for Enro-C and Enro-R, respectively. Monte Carlo simulations based on Cmax /MIC90  = 10 indicate that only Enro-C15 and Enro-C20 may be useful to treat leptospirosis in cows, predicting a success rate ≥95% when MIC50  = 0.5 µg/ml, and ≥80% when MIC90  = 1.0 µg/ml. Although Enro-C15 and Enro-C20 may be useful to treat leptospirosis in cattle, clinical trials are necessary to confirm this proposal.

Antimicrobial Resistance in Leptospira, Brucella, and Other Rarely Investigated Veterinary and Zoonotic Pathogens.

Leptospira, Brucella, and Borrelia are major agents of zoonotic disease, causing high morbidity and, in some cases, significant mortality in humans. For all three genera, prompt diagnosis and appropriate antimicrobial therapy are required to prevent the development of chronic, debilitating illness. Leptospira spp. are intrinsically resistant to several antimicrobial classes; however, there is little evidence in the literature for development of acquired resistance to antimicrobial agents used for clinical treatment of acute leptospirosis. For Brucella infections, there are numerous reports of relapses following therapy, but it is unclear whether this is due to sequestration within infected sites (e.g., bone) or the development of acquired resistance. Brucella have maintained their susceptibility to doxycycline and rifampicin, which in combination remain the most common treatments of brucellosis in humans. In vitro induced point mutations are described as imparting resistance to rifampicin (rpoB) and fluoroquinolones (gyrA). The clinical significance of these mutations is unclear. For Borrelia burgdorferi, although acquired resistance to some antimicrobial agents has been described, resistance due to bacterial persister cells surviving in the presence of antimicrobial, with no apparent increase in the MIC of the organism, have been recently described. Of the remaining veterinary fastidious pathogens, Lawsonia intracellularis is the most interesting from an antimicrobial resistance perspective because it can only be grown in cell culture, making in vitro susceptibility testing challenging. MIC testing has been undertaken on a small number of isolates, and some differences in susceptibility to macrolides have been demonstrated between isolates obtained from different regions.

Advances & challenges in leptospiral vaccine development.

Considerable progress has been made in the field of leptospiral vaccines development since its first use as a killed vaccine in guinea pigs. Despite the fact that the immunity conferred is restricted to serovars with closely related lipopolysaccharide antigen, certain vaccines have remained useful, especially in endemic regions, for the protection of high-risk individuals. Other conventional vaccines such as the live-attenuated vaccine and lipopolysaccharide (LPS) vaccine have not gained popularity due to the reactive response that follows their administration and the lack of understanding of the pathogenesis of leptospirosis. With the recent breakthrough and availability of complete genome sequences of Leptospira, development of novel vaccine including recombinant protein vaccine using reverse vaccinology approaches has yielded encouraging results. However, factors hindering the development of effective leptospiral vaccines include variation in serovar distribution from region to region, establishment of renal carrier status following vaccination and determination of the dose and endpoint titres acceptable as definitive indicators of protective immunity. In this review, advancements and progress made in LPS-based vaccines, killed- and live-attenuated vaccines, recombinant peptide vaccines and DNA vaccines against leptospirosis are highlighted.

Leptospirosis among Returned Travelers: A GeoSentinel Site Survey and Multicenter Analysis-1997-2016.

Leptospirosis is a potentially fatal emerging zoonosis with worldwide distribution and a broad range of clinical presentations and exposure risks. It typically affects vulnerable populations in (sub)tropical countries but is increasingly reported in travelers as well. Diagnostic methods are cumbersome and require further improvement. Here, we describe leptospirosis among travelers presenting to the GeoSentinel Global Surveillance Network. We performed a descriptive analysis of leptospirosis cases reported in GeoSentinel from January 1997 through December 2016. We included 180 travelers with leptospirosis (mostly male; 74%; mostly tourists; 81%). The most frequent region of infection was Southeast Asia (52%); the most common source countries were Thailand (N = 52), Costa Rica (N = 13), Indonesia, and Laos (N = 11 each). Fifty-nine percent were hospitalized; one fatality was reported. We also distributed a supplemental survey to GeoSentinel sites to assess clinical and diagnostic practices. Of 56 GeoSentinel sites, three-quarters responded to the survey. Leptospirosis was reported to have been most frequently considered in febrile travelers with hepatic and renal abnormalities and a history of freshwater exposure. Serology was the most commonly used diagnostic method, although convalescent samples were reported to have been collected infrequently. Within GeoSentinel, leptospirosis was diagnosed mostly among international tourists and caused serious illness. Clinical suspicion and diagnostic workup among surveyed GeoSentinel clinicians were mainly triggered by a classical presentation and exposure history, possibly resulting in underdiagnosis. Suboptimal usage of available diagnostic methods may have resulted in additional missed, or misdiagnosed, cases.

Leptospirosis: An important zoonosis acquired through work, play and travel

BACKGROUND: Leptospirosis is one of the most common zoonotic diseases worldwide. Infection occurs through contact with infected animals, or soil or water that has been contaminated by the urine of infected animals. Risk factors include occupational and recreational exposures, contact with floodwaters, and travel to areas with a high risk of leptospirosis, particularly tropical, developing countries. With climate change, flood-related outbreaks are becoming more common. OBJECTIVE: This article aims to improve awareness of leptospirosis, and provide an update for general practitioners on its epidemiology, risk factors, clinical presentation, laboratory diagnosis, management and prevention. DISCUSSION: Leptospirosis is sometimes misdiagnosed because clinical presentation can be non-specific and overlap with many other causes of acute febrile illnesses. In patients with risk factors for leptospirosis, a high index of clinical suspicion is important to ensure early diagnosis and treatment. Delays in treatment could increase the risk of severe complications, including pulmonary haemorrhage, acute renal failure and acute liver failure.

Low-dose Norfloxacin-treated leptospires induce less IL-1ß release in J774A.1 cells following discrepant leptospiral gene expression.

Currently, accumulating evidence is challenging subtherapeutic therapy. Low-dose Norfloxacin (Nor) has been reported to suppress the immune response and worsen leptospirosis. In this study, we investigated the influence of low-dose Nor (0.03 µg/ml, 0.06 µg/ml, 0.125 µg/ml) on leptospiral gene expression and analyzed the immunomodulatory effects of low-dose Nor-treated leptospires in J774A.1 cells. To study the expression profiles of low-dose Nor-treated leptospires, we chose LipL71/LipL21 as reference genes determined by the geNorm applet in this experiment. The results showed that low-dose Nor up-regulated the expression of FlaB and inhibited the expression of 16S rRNA, LipL32, LipL41, Loa22, KdpA, and KdpB compared with the untreated leptospires. These results indicated that low-dose Nor could regulate leptospiral gene expression. Using RT-PCR, the gene expression of IL-1ß and TNF-α in J774A.1 cells was detected. Nor-treated leptospires induced higher expression levels of both IL-1ß and TNF-α. However, when analyzed by ELISA, the release of mature IL-1ß was reduced compared with that observed in cells induced with no Nor-treated leptospires, although the TNF-α protein level showed no significant change. Our study indicated that the gene expression of leptospires could be modulated by low-dose Nor, which induced less IL-1ß release in J774A.1 cells.

Pharmacokinetics of enrofloxacin HCl-2H2O (Enro-C) in dogs and pharmacokinetic/pharmacodynamic Monte Carlo simulations against Leptospira spp.

Pharmacokinetic/pharmacodynamic (PK/PD) ratios of reference enrofloxacin (Enro-R) and enrofloxacin as HCl-2H2O (Enro-C), as well as Monte Carlo simulations based on composite MIC50 and MIC90 (MIC, minimum inhibitory concentration) vs. Leptospira spp., were carried out in dogs after their intramuscular (IM) or oral administration (10 mg/kg). Plasma determination of enrofloxacin was achieved by means of high-performance liquid chromatography. Maximum plasma concentration values after oral administration were 1.47 ± 0.19 µg/mL and 5.3 ± 0.84 µg/mL for Enro-R and Enro-C, respectively, and 1.6 ± 0.12 µg/mL and 7.6 ± 0.93 µg/mL, respectively, after IM administration. Areas under the plasma vs. time concentration curve in 24 h (AUC0-24) were 8.02 µg/mL/h and 36.2 µg/mL/h for Enro-Roral and Enro-Coral, respectively, and 8.55 ± 0.85 µg/mL/h and 56.4 ± 6.21 µg/mL/h after IM administration of Enro-R and Enro-C, respectively. The PK/PD ratios and Monte Carlo simulations obtained with Enro-C, not Enro-R, indicated that its IM administration to dogs will result in therapeutic concentrations appropriate for treating leptospirosis. This is the first time enrofloxacin has been recommended to treat this disease in dogs.

Can Subminimal Inhibitory Concentrations of Antibiotics Induce the Formation of Biofilm in Leptospira?

Antibiotics at subminimal inhibitory concentrations (sub-MICs) are known to induce biofilm formation in numerous bacteria in vitro. In this report, the effect of sub-MIC levels of antibiotics (doxycycline and tetracycline) on biofilm formation by leptospiral reference strains and isolates was investigated. The sub-MIC levels of both tetracycline and doxycycline were able to induce biofilm in some of the leptospiral strains. This is the first report demonstrating the effect of sub-MIC level of antibiotics in inducing biofilm formation in Leptospira. The induction of biofilm may solely be a response to the amount of threshold stress enforced by low levels of antibiotics. The mechanism of biofilm induction by subinhibitory antibiotic concentrations needs to be explored further. Studies are required to understand the clinical relevance of the phenomenon and its contribution to biofilm formation in the host, resulting in the failure of antimicrobial therapy during the treatment of chronic leptospirosis.

Evaluation of inhibitors for development of a selective medium for isolation of Leptospira spp. from clinical samples.

This study was conducted to develop a selective medium for the detection of Leptospira spp. in clinical samples. Serovars of Leptospira spp., environmental bacteria and the fungus from contaminated cultures of patients with suspected leptospirosis were inoculated into EMJH medium containing amphotericin B, 5-fluorouracil (5-FU), furazolidone and neomycin used singly or combined. Medium with 5-FU at the concentration of 200 µg ml-1 did not show any inhibitory effect against the fungus, Gram-negative bacilli and any of the leptospira strains except serovar Pyrogenes. The highest concentration of neomycin and furazolidone that did not inhibit the growth of leptospires was 4 µg ml-1 . All strains of Leptospira spp. grew on 5-FU (100 µg ml-1 ) in combination with neomycin (4 µg ml-1 ) and on 5-FU (100 µg ml-1 ) in combination with furazolidone (4 µg ml-1 ). The highest concentration of amphotericin B (500 µg ml-1 ) that inhibited the growth of the fungus also inhibited the bacteria and most of serovars of Leptospira spp. The most effective antibiotic combinations that inhibited the majority of environmental bacteria growth without affecting leptospiral growth were EMJH with 5-FU (100 µg ml-1 ) in combination with neomycin (4 µg ml-1 ). In conclusion, these findings will help the development of new selective media to isolate leptospires. SIGNIFICANCE AND IMPACT OF THE STUDY: Leptospirosis is one of the most widespread zoonotic diseases in the world. Since certain serovars are often associated with the symptoms and severity of the disease, the isolation and identification of the leptospires usually permits the prediction of sources of infection. Attempts to isolate Leptospira spp. from clinical specimens are often frustrated by overgrowth of the slow-growing bacteria by more rapidly growing contaminants. In this study, we evaluated selective agents to develop a new selective medium to isolate leptospires. The results demonstrated that the association of drugs in concentrations that allowed the growth of leptospires is to be more effective in inhibiting bacterial contaminants.

Antibiotic susceptibilities of livestock isolates of leptospira.

Leptospirosis is the most common zoonotic disease and is endemic worldwide. The antibiotic susceptibilities of Leptospira strains isolated from both humans and animals are poorly documented. This issue is particularly important for isolates from food-producing animals which are regularly exposed to antibiotic treatments. This study assessed the susceptibility of 35 leptospira strains isolated from food-producing animals of diverse geographical origins between 1936 and 2016 to the antimicrobial agents used most commonly in animals. A broth microdilution method was used to determine the susceptibilities of Leptospira strains isolated from livestock to 11 antibiotics. All isolates were susceptible to penicillin, amoxicillin, clavulanate, cephalexin, ceftriaxone, doxycycline, tetracycline, streptomycin, enrofloxacin and spectinomycin, but not polymyxin [minimum inhibitory concentration (MIC) ≥ 4 µg/L]. For tetracycline and doxycycline, the MIC was significantly higher for the recent isolates from Sardinia, Italy than for the other isolates. Antimicrobial susceptibilities were also determined with 10- and 100-fold higher inocula. High inocula significantly diminished the antibacterial effect by at least 10-fold for enrofloxacin (MIC ≥256 µg/L), streptomycin (MIC ≥16 µg/L) and tetracycline (MIC ≥32 µg/L), suggesting selection of resistant strains for high inocula. These findings contribute to the assessment of whether certain antibiotics are potentially useful for the treatment of leptospirosis, and point out the risk of failure for some antibiotics during infection with a high inoculum in both animals and humans. This study strengthens the need to detect and prevent the emergence of antimicrobial resistance of this major emerging zoonotic pathogen.

Characterization of Leptospira species isolated from soil collected in Japan.

Leptospira were isolated from soil obtained from Hokkaido, the northernmost island, to Okinawa, the southernmost island, of Japan using sulfamethoxazole, trimethoprim, amphotericin B, fosfomycin, and 5- fluorouracil. Fifty of 132 soil samples (37.9%) were culture-positive. On the basis of 16S-rDNA sequences, 12 of the isolated Leptospira were classified into a pathogenic species clade that is closely associated with L. alstonii and L. kmetyi. Nine isolates were classified as intermediate species and were found to be similar to L. licerasiae. Twenty-seven isolates were classified as non-pathogenic species, of which 23 were found to be related to L. wolbachii. Non-pathogenic Leptospira are commonly distributed in environmental soil.

Potential anti-leptospiral compound, leptomycin B from marine Streptomyces indiaensis MSU5: taxonomy, fermentation, compound isolation, in vitro and in vivo efficacy.

Leptospirosis is a worldwide reemerging tropical zoonotic disease with symptoms of mild febrile illness to more severe multiple organ failure caused by pathogenic leptospiral strains. There was no effective antibiotic for treating leptospirosis. Here, the anti-leptospiral potential of marine actinobacterial compound from Streptomyces indiaensis MSU5 isolated from Manakudy marine sediment, Tamil Nadu, India was evaluated. The potential actinobacterial strain was identified by phenotypic, cell wall, 16S rRNA gene sequence and phylogenetic analysis. In vitro anti-leptospiral activity of the actinobacterial compound was determined using broth microdilution test against various serovars of Leptospira with different concentration ranging from 15.625 to 500 µg/ml. Mass production of anti-leptospiral compound was carried out in agar surface fermentation with optimized condition and purified by preparative TLC. The purified fraction of anti-leptospiral compound named as MSU5-1, and it was confirmed by microdilution test. Remarkably, the compound MSU5-1 showed minimum inhibitory concentration of 62.5 µg/ml and minimum bactericidal concentration of 125 µg/ml against human pathogenic leptospiral isolate strain N2. The structural elucidation of purified compound was carried out using UV, FT-IR, NMR and LC-MS analysis. The compound MSU5-1 was tentatively identified as leptomycin B (C33H48O6) with molecular weight 541.1 g/mol. Anti-leptospiral activity of compound MSU5-1 exhibited 80% of survival rate in mice model, further it was confirmed by Quantitative Real-Time Polymerase Chain Reaction (qRT-PCR) analysis. From the available literature, this is the first report on the marine actinobacterial compound for evaluating both in vitro and in vivo leptospiricidal activity.

Antimicrobial susceptibility of Leptospira spp. isolated from environmental, human and animal sources in Malaysia.

Leptospirosis is a zoonosis with worldwide distribution caused by pathogenic spirochetes of the genus Leptospira. The aim of this study was to evaluate the susceptibility of isolates obtained from different hosts. A total of 65 Leptospira isolates from humans (n = 1), zoonoses (rat, n = 60; dog, n = 1; swine, n = 1) and environment (n = 2) were tested against six antibiotics. All the isolates were resistant to trimethoprim and sulphamethoxazole and had high MIC toward chloramphenicol (MIC90: 6.25 µg/ml). All except one environment isolate were sensitive to ampicillin, doxycycline and penicillin G.

Discovery of 6,7-dihydro-3H-pyrano[4,3-c]isoxazol-3-ones as a new class of pathogen specific anti-leptospiral agents.

A simple and efficient method for the synthesis of a series of 6,7-dihydro-3H-pyrano[4,3-c]isoxazol-3-one derivatives starting from 5-carboalkoxy-2,3-dihydropyranone (5-CDHPs) has been developed. Pyranoisoxazolones 10a-j, dihydronaphthopyran-4-one (DHNPs) class of natural product 12b and 12c and its analogues 12a and 13a-c were preliminarily screened against pathogenic leptospiral serovar Autumnalis strain N2 at various concentrations. Six pyranoisoxazolones, 10b, 10d, 10f, 10g, 10i and 10j which displayed very good anti-leptospiral activity was taken for secondary screening against twelve strains of pathogenic and one non-pathogenic leptospiral serovars. While all the compounds displayed significant anti-leptospiral activity against the pathogenic serovars at MIC of 62.5-500 µg/mL. Compounds 10d, 10g and 10j did not show any significant effect on non-pathogenic serovar. Inhibition of leptospires at a significant level by pyranoisoxazolone 10g was confirmed using RT-qPCR assay. In vivo treatment of BALB/c mice with compound 10g revealed that, it has 95% survivability against the pathogenic strain Canicola and also showed inhibition of renal colonization of leptospires. Compound 10g was found to show cytotoxicity against THP-1 cells only at higher concentration (≥75 µg/mL). Effective binding of compound 10g with leptospiral outer membrane protein LipL32 observed via in silico molecular docking provided a suitable explanation for pathogen specificity of compound 10g. Antibiotics acting against leptospirosis in human are very few. The results obtained from in vitro, in vivo and in silico study reveals that 6,7-dihydro-3H-pyrano[4,3-c]isoxazol-3-ones class of compounds are lead molecules for further development as pathogen specific anti-leptospiral agents.