Efficacy of fluoroquinolones against Leptospira interrogans in a hamster model

Double-trouble: A rare case of co-infection with melioidosis and leptospirosis from Sri Lanka

Melioidosis and leptospirosis are two emerging tropical infections that share somewhat similar clinical manifestations but require different methods of management. A 59-year-old farmer presented to a tertiary care hospital with an acute febrile illness associated with arthralgia, myalgia and jaundice, complicated by oliguric acute kidney injury and pulmonary haemorrhage. Treatment was initiated for complicated leptospirosis but with poor response. Blood culture was positive for Burkholderia pseudomallei and microscopic agglutination test (MAT) for leptospirosis was positive at the highest titres of 1:2560, confirming a co-infection of leptospirosis and melioidosis. The patient made a complete recovery with therapeutic plasma exchange (TPE), intermittent haemodialysis and intravenous (IV) antibiotics. Similar environmental conditions harbour melioidosis and leptospirosis, making co-infection a very real possibility. Co-infection should be suspected in patients from endemic areas with water and soil exposure. Using two antibiotics to cover both pathogens effectively is prudent. IV penicillin with IV ceftazidime is one such effective combination.

Treatment of Bovine Leptospirosis with Enrofloxacin HCl 2H2O (Enro-C): A Clinical Trial

Pharmacokinetics/pharmacodynamics ratios of enrofloxacin HCl-2H2O (enro-C) in cows to treat bovine leptospirosis prompted this clinical trial in the highlands (HL) and the tropics (TL) in Mexico. In the HL, 111 Holstein-Friesian cows were included and 38 F1 Zebu–Holstein/Friesians in the TL. Affected cows were randomly divided into two treatment groups, both in the HL and TL. PCR and MAT tests were performed before and after treatment. Treatments in both groups were administered for 5 d with either IM injections of enro-C or streptomycin/penicillin-G. Reproductive performance data were gathered for 90 d. The cows treated with enro-C became PCR negative: 87.5% and 78.94% on day 5, 92.85% and 94.73% on day 28 (in the HL and TL, respectively). For streptomycin/penicillin-G, the same values were 65.45% and 70.90% on day 5, and 73.68% twice on day 28 in the HL and TL, respectively. In both groups and geographical settings, the MAT titers dropped on day 28 but remained above reference values usually considered negative. The gestation rates were: 86.53% and 79.06% and 88.88% and 87.5% for the HL and TL, either with enro-C or streptomycin/penicillin-G, respectively. This is the first report of successful treatment with a fluoroquinolone derivative in treating bovine leptospirosis with a high bacteriological cure rate.

Outpatient Clinical Trial in Dogs With Leptospirosis Treated With Enrofloxacin Hydrochloride-Dihydrate (ENRO-C)

Pharmacokinetics of enrofloxacin HCl-2H2O (enro-C) in dogs and Monte-Carlo simulations against Leptospira spp. prompted a clinical study to treat the clinically apparent phase of this disease. Leptospirosis was diagnosed by real-time PCR from blood, micro-agglutination titers (MAT), clinical signs and blood parameters of the liver and kidney. In order to determine the clinical ability of the participants to diagnose leptospirosis on the first exam and establish an early treatment to avoid excessive organ damage, patients were clinically classified as: high-risk or medium-risk. Forty-five dogs were included in this trial (from 2017 to early 2019). The treatment consisted of IM injections of a 5% aqueous enro-C suspension (10 mg/kg/day) for 10 days, and subsequently enro-C was administered orally for another 7 days in gelatin capsules. Thirty-four high-risk and 11 medium-risk dogs were treated, including 6 puppies (4 high-risk with ages between 6 to 10 months and 2 medium-risk dogs with an average age of 6 and 7 months). Other ages ranged from 1 to 5 years. Fifteen cases had a history of having received prior treatment with other antibiotics, including all puppies. The clinical diagnostic error was 13.5% (7/52 cases), and only one of the misdiagnosed dogs had been classified as a high-risk patient. Three to 5 days after finishing treatment with enro-C, 82.2% of the dogs were negative to real-time PCR from urine samples and 100% negativity was observed on day 30 after treatment, when antibody titrations dropped to 1:100-1:200. Based on the absence of clinical signs, real-time PCR, and MAT titers, all treated dogs were considered as successful treatments. Within 6-24 months of clinical follow-up, no relapses were recorded. Adverse effects were inconsequential. This study represents the first report of a successful treatment of canine leptospirosis using a fluoroquinolone, and due to its efficacy, it is suggested that enro-C be considered as a viable option for the treatment of this disease.

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 (C_max /MIC₉₀ ) and area under the serum vs. time concentration of enrofloxacin/MIC (AUC_0-24 /MIC₉₀ ). Monte Carlo simulations targeted C_max /MIC = 10 and AUC_0-24 /MIC = 125. Mean C_max 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. C_max /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 C_max /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.

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 (AUC_0–24) were 8.02 µg/mL/h and 36.2 µg/mL/h for Enro-R_oral and Enro-C_oral, 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.

Persistent Leptospiruria in Five Dogs Despite Antimicrobial Treatment (2000-2017)

In dogs with leptospirosis, doxycycline therapy is recommended as the preferred therapy for its ability to eliminate the organism from all tissues, including the renal tubules. Elimination of organisms from the renal tubules terminates leptospiruria and prevents transmission of the organism. This report describes the discovery of persistent leptospiruria in the face of therapy with doxycycline in four dogs and enrofloxacin in one dog. Leptospiruria was confirmed by polymerase chain reaction testing for pathogenic leptospires in all five dogs. In two dogs, leptospiruria resolved after a change in therapy to enrofloxacin. In three dogs, doxycycline and/or enrofloxacin were ineffective at eliminating leptospiruria, which then resolved after therapy with clarithromycin. Pet owners could be at risk as persistent leptospiruria poses a potential zoonotic risk. The potential reasons for persistent leptospiruria as demonstrated by polymerase chain reaction testing are discussed.

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.

Efficacy of a New Recrystallized Enrofloxacin Hydrochloride-Dihydrate against Leptospirosis in a Hamster Model

A trial on Syrian hamsters (Mesocricetus auratus) infected with Leptospira interrogans serovar Canicola was established to compare treatment efficacies of daily intramuscular (i.m.) injections of either 10 mg/kg of 5% enrofloxacin (Baytril [BE]; Bayer Animal Health, Mexico) or the same dose of enrofloxacin hydrochloride-dihydrate (enro-C). Hamsters were experimentally infected via the oral submucosa with 400 microorganisms/animal, in a sequential time schedule aligned to the initial treatment day, and were treated in groups as follows: a group treated with 5% enrofloxacin daily for 7 days after 24 h of infection (group BE₂₄); a group treated as described for group BE₂₄ but with enro-C (enro-C₂₄); a group also treated with 5% enrofloxacin but starting at 72 h after infection (BE₇₄); a group treated as described for group BE₇₄ but with injection of enro-C (enro-C₇₄). An untreated-uninfected control group (group CG^-) and an infected-untreated control group (group CG⁺) were assembled (n = 18 in all groups). Weights and temperatures of the hamsters were monitored daily for 28 days. After hamsters were euthanatized or following death, necropsy, histopathology, macroscopic agglutination tests (MAT), bacterial culture, and PCR were performed. The mortality rates were 38.8% in group BE₂₄ and 100% in group BE₇₄ No mortality was observed in group enro-C₂₄, and 11.1% mortality was recorded in group enro-C₇₄ The mortality rates in groups CG⁺ and CG^- were 100% and zero, respectively. Combined necropsy and histopathologic findings revealed signs of septicemia and organ damage in groups BE₂₄, BE₇₂, and CG⁺ Groups enro-C₂₄ and CG^- showed no lesions. Moderated lesions were registered in 3 hamsters in group enro-C₇₂ MAT results were positive in 83.3% of BE₂₄ hamsters (83.3%) and 100% of BE₇₂ and CG⁺ hamsters; MAT results were positive in 16.7% in group Enro-C₂₄ and 38.9% in group enro-C₇₂ Only 4/18 were PCR positive in group enro-C₇₂ and only 1 in group enro-C₂₄ (P < 0.05). It can be concluded that enro-C may be a viable option to treat leptospirosis in hamsters and that this may be the case in other species.

Doxycycline Attenuates Leptospira-Induced IL-1β by Suppressing NLRP3 Inflammasome Priming

Doxycycline (Dox), a semisynthetic antibiotic, has been reported to exert multiple immunomodulatory effects. Treatment with Dox has a satisfactory curative effect against leptospirosis. In addition to its antibacterial action, we supposed that Dox also modulated immune response in controlling leptospira infection. Using J774A.1 mouse macrophages, the effects of Dox on protein and mRNA levels of IL-1β and TNF-α were investigated after infection with live or sonicated Leptospira interrogans serovar Lai strain Lai (56601). Specifically, the level of IL-1β but not TNF-α was sharply decreased when treated with Dox in leptospira-infected macrophages. Western blot analysis showed that Dox suppressed the activation of leptospira-induced MAPK and NF-κB signaling pathways. Using NLRP3-deficient and NLRC4-deficient mice, the data showed that the expression of leptospira-induced IL-1β was mainly dependent on the presence of NLRP3 inflammasome in macrophages. Meanwhile, Dox suppressed leptospira-induced NLRP3 inflammasome priming with the upregulation of the Na/K-ATPase Pump β1 subunit. The inhibition effect of Dox on IL-1β was also conspicuous in cells with lipopolysaccharide and ATP stimulation. These results were confirmed in vivo, as peritoneal fluids of mice and organs of hamsters expressed less IL-1β after treatment of leptospiral infection with Dox. Our results indicated that Dox also modulated immune response to attenuate leptospira-induced IL-1β by suppressing p38, JNK, p65, and NLRP3 inflammasome priming.

[Leptospirosis in French Guiana and the Guiana shield: Current knowledge in 2016]

Leptospirosis is a cosmopolitan zoonosis caused by bacteria of the genus Leptospira. Whether the distribution is worldwide, the hot and humid climate of the tropics is particularly conducive to its expansion. In most French overseas departments and territories, leptospirosis is considered as a public health problem. In French Guiana, a French department located in the northeastern part of the Amazon rainforest, it is supposed to be rare. The objective of this review was to make an inventory of the knowledge on human and animal leptospirosis in French Guiana and neighboring countries. A comprehensive search was conducted through the indexed and informal medical literature in English, French, Spanish and Portuguese. Thus, respectively ten and four publications were identified on human and animal leptospirosis in French Guiana, published between 1940 and 1995 in the form of case reports or case series. The publications concerning this disease in the other countries of the Guiana Shield, eastern Venezuela, Guyana, Suriname, and Brazilian state of Amapá, also scarce or nonexistent. However recent data from the French National Centre of leptospirosis showed a recent and sudden increase in the number of cases in the department, probably partly due to the development of diagnostic tools such as Elisa IgM serology. It is likely that leptospirosis is a neglected disease in the region, due to the lack of diagnostic tools readily available, the lack of knowledge of the local clinicians on this disease and the existence of many other pathogens with similar clinical presentation such as malaria, arboviruses and Q fever and Amazonian toxoplasmosis. The establishment of more large-scale studies on animal and human leptospirosis is necessary and urgent to know the true burden of this disease in our region.

Low-dose norfloxacin and ciprofloxacin therapy worsen leptospirosis in hamster

Antibiotics play an important role in the treatment of leptospirosis. Many antibiotics at appropriate concentrations improved the survival rate and alleviated tissue injury, while, when dosing strategies fall below subtherapeutic levels, worse therapeutic effects are seen. In the present study, we investigated the efficacy of low-dose norfloxacin (10, 20 and 30 mg/kg) and ciprofloxacin (1, 2 and 5 mg/kg) against leptospirosis in a hamster model using Leptospira interrogans serovar Icterohaemorrhagiae. The histopathology and bacterial loads of target organs (liver, kidney and lung) were also studied by treatment with norfloxacin at the dose of 10 mg/kg in this model. Using RT-PCR, the expression of inflammatory factor IL-1β and TNF-α was analyzed by comparing the norfloxacin and untreated group. All untreated animals, serving as a negative control, displayed 50% survival rate, while hamsters treated with norfloxacin at the dose of 10 and 20 mg/kg and ciprofloxacin at the dose of 1 and 2 mg/kg showed a lower survival rate than the untreated group. Furthermore, norfloxacin at the dose of 10 mg/kg increased bacterial loads and aggravated tissue injury of target organs. The delayed induction of IL-1β and TNF-α was found in tissues of norfloxacin group. Our study indicates an increased risk associated with low-dose norfloxacin and ciprofloxacin in leptospirosis.

Comparative analyses of transport proteins encoded within the genomes of Leptospira species

Select species of the bacterial genus Leptospira are causative agents of leptospirosis, an emerging global zoonosis affecting nearly one million people worldwide annually. We examined two Leptospira pathogens, Leptospira interrogans serovar Lai str. 56601 and Leptospira borgpetersenii serovar Hardjo-bovis str. L550, as well as the free-living leptospiral saprophyte, Leptospira biflexa serovar Patoc str. 'Patoc 1 (Ames)'. The transport proteins of these leptospires were identified and compared using bioinformatics to gain an appreciation for which proteins may be related to pathogenesis and saprophytism. L. biflexa possesses a disproportionately high number of secondary carriers for metabolite uptake and environmental adaptability as well as an increased number of inorganic cation transporters providing ionic homeostasis and effective osmoregulation in a rapidly changing environment. L. interrogans and L. borgpetersenii possess far fewer transporters, but those that they all have are remarkably similar, with near-equivalent representation in most transporter families. These two Leptospira pathogens also possess intact sphingomyelinases, holins, and virulence-related outer membrane porins. These virulence-related factors, in conjunction with decreased transporter substrate versatility, indicate that pathogenicity arose in Leptospira correlating to progressively narrowing ecological niches and the emergence of a limited set of proteins responsible for host invasion. The variability of host tropism and mortality rates by infectious leptospires suggests that small differences in individual sets of proteins play important physiological and pathological roles.

Comparative genomic analyses of transport proteins encoded within the genomes of Leptospira species

Select species of the bacterial genus Leptospira are causative agents of leptospirosis, an emerging global zoonosis affecting nearly one million people worldwide annually. We examined two Leptospira pathogens, Leptospira interrogans serovar Lai str. 56601 and Leptospira borgpetersenii serovar Hardjo-bovis str. L550, as well as the free-living leptospiral saprophyte, Leptospira biflexa serovar Patoc str. 'Patoc 1 (Ames)'. The transport proteins of these leptospires were identified and compared using bioinformatics to gain an appreciation for which proteins may be related to pathogenesis and saprophytism. L. biflexa possesses a disproportionately high number of secondary carriers for metabolite uptake and environmental adaptability as well as an increased number of inorganic cation transporters providing ionic homeostasis and effective osmoregulation in a rapidly changing environment. L. interrogans and L. borgpetersenii possess far fewer transporters, but those that they have are remarkably similar, with near-equivalent representation in most transporter families. These two Leptospira pathogens also possess intact sphingomyelinases, holins, and virulence-related outer membrane porins. These virulence-related factors, in conjunction with decreased transporter substrate versatility, indicate that pathogenicity was accompanied by progressively narrowing ecological niches and the emergence of a limited set of proteins responsible for host invasion. The variability of host tropism and mortality rates by infectious leptospires suggests that small differences in individual sets of proteins play important physiological and pathological roles.

In vitro and in vivo activity of first generation cephalosporins against Leptospira

Third generation cephalosporins are commonly used in the treatment of leptospirosis. The efficacy of first generation cephalosporins has been less well-studied. Susceptibility testing of 13 Leptospira strains (11 serovars) to cefazolin and cephalexin was conducted using broth microdilution. Median minimal inhibitory concentration (MIC) for cefazolin and cephalexin ranged from < 0.016 to 2 μg/mL (MIC(90) = 0.5 μg/mL) and from 1 to 8 μg/mL (MIC(90) = 8 μg/mL), respectively. Efficacy of cefazolin and cephalexin in an acute lethal hamster model of leptospirosis was studied. Survival rates for cefazolin were 80%, 100%, and 100%, and survival rates for cephalexin were 50%, 80%, and 100% (treated with 5, 25, and 50 mg/kg per day for 5 days, respectively). Each treatment group showed improved survival compared with no treatment (P < 0.01), and none of the therapies, regardless of dose, was statistically significantly different than doxycycline. These results support a potential role for first generation cephalosporins as alternative therapies for leptospirosis.

2010 ACVIM small animal consensus statement on leptospirosis: diagnosis, epidemiology, treatment, and prevention

This report offers a consensus opinion on the diagnosis, epidemiology, treatment, and prevention of leptospirosis in dogs, an important zoonosis. Clinical signs of leptospirosis in dogs relate to development of renal disease, hepatic disease, uveitis, and pulmonary hemorrhage. Disease may follow periods of high rainfall, and can occur in dogs roaming in proximity to water sources, farm animals, or wildlife, or dogs residing in suburban environments. Diagnosis is based on acute and convalescent phase antibody titers by the microscopic agglutination test (MAT), with or without use of polymerase chain reaction assays. There is considerable interlaboratory variation in MAT results, and the MAT does not accurately predict the infecting serogroup. The recommended treatment for optimal clearance of the organism from renal tubules is doxycycline, 5 mg/kg PO q12h, for 14 days. Annual vaccination can prevent leptospirosis caused by serovars included in the vaccine and is recommended for dogs at risk of infection.

In vitro sensitivity and resistance of 46 Leptospira strains isolated from rats in the Philippines to 14 antimicrobial agents

The in vitro susceptibilities of 46 Leptospira isolates from rats to 14 antimicrobial agents were tested. All of the strains were found to be sensitive to ampicillin, cefotaxime, ciprofloxacin, norfloxacin, doxycycline, erythromycin, and streptomycin. In contrast, the tested isolates showed resistance to amphotericin B, 5-fluorouracil, fosfomycin, trimethoprim, sulfamethoxazole, neomycin, and vancomycin. These findings will help in selecting effective and ineffective antimicrobials for treatment of leptospirosis and for the development of new selective media, respectively.

Functional characterization of GDP-mannose pyrophosphorylase from Leptospira interrogans serovar Copenhageni

Leptospira interrogans synthesizes a range of mannose-containing glycoconjugates relevant for its virulence. A prerequisite in the synthesis is the availability of the GDP-mannose, produced from mannose-1-phosphate and GTP in a reaction catalyzed by GDP-mannose pyrophosphorylase. The gene coding for a putative enzyme in L. interrogans was expressed in Escherichia coli BL21(DE3). The identity of this enzyme was confirmed by electrospray-mass spectroscopy, Edman sequencing and immunological assays. Gel filtration chromatography showed that the dimeric form of the enzyme is catalytically active and stable. The recombinant protein was characterized as a mannose-1-phosphate guanylyltransferase. S (0.5) for the substrates were determined both in GDP-mannose pyrophosphorolysis: 0.20 mM (GDP-mannose), 0.089 mM (PPi), and 0.47 mM; and in GDP-mannose synthesis: 0.24 mM (GTP), 0.063 mM (mannose-1-phosphate), and 0.45 mM (Mg(2+)). The enzyme was able to produce GDP-mannose, IDP-mannose, UDP-mannose and ADP-glucose. We obtained a structural model of the enzyme using as a template the crystal structure of mannose-1-phosphate guanylyltransferase from Thermus thermophilus HB8. Binding of substrates and cofactor in the model agree with the pyrophosphorylases reaction mechanism. Our studies provide insights into the structure of a novel molecular target, which could be useful for detection of leptospirosis and for the development of anti-leptospiral drugs.

Protein typing of major outer membrane lipoproteins from Chinese pathogenic Leptospira spp. and characterization of their immunogenicity

Leptospirosis, caused by different Leptospira species, is one of the most widespread zoonotic infections worldwide. Here we expressed three major leptospiral lipoproteins and examined their immunogenicity. All the pathogenic Leptospira strains tested possess the lipL21, lipL32 and lipL41 genes, but the latter two can be further divided into different gene types (lipL32-1, lipL32-2, lipL41-1, lipL41-2). Microscopic agglutination test revealed that rLipLs antisera had extensive cross-immunoagglutination among the 178 leptospiral strains in which rLipL32-1 contributed the highest agglutination titer. The rLipLs-based ELISAs established in this study demonstrated that in the sera of 385 leptospirosis patients infected with different serovars of Leptospira interrogans, rLipL32-1 had the highest positive rates for IgG and IgM (89.4-98.7%), followed by the IgG/IgM positive rates of rLipL21 (87.0-96.1%) and rLipL32-2 (86.5-96.9%), while the two rLipL41s presented the lowest IgG/IgM positive rates (69.9-83.9%). The immunoprotective levels in guinea pigs of rLipL32-1 (58.3% and 66.7%) were the highest, compared to those of the other rLipLs (25.0-58.3%). Multiple different rLipLs would increase immunoprotective levels (from 58.3% and 66.7% to 83.3% and 91.7%). The data suggest that all the rLipLs are the genus-specific superficial antigens of pathogenic Leptospira species and should be considered in designing universal vaccines against leptospirosis.

Antimicrobial susceptibilities of geographically diverse clinical human isolates of Leptospira

Although antimicrobial therapy of leptospirosis has been studied in a few randomized controlled clinical studies, those studies were limited to specific regions of the world and few have characterized infecting strains. A broth microdilution technique for the assessment of antibiotic susceptibility has been developed at Brooke Army Medical Center. In the present study, we assessed the susceptibilities of 13 Leptospira isolates (including recent clinical isolates) from Egypt, Thailand, Nicaragua, and Hawaii to 13 antimicrobial agents. Ampicillin, cefepime, azithromycin, and clarithromycin were found to have MICs below the lower limit of detection (0.016 microg/ml). Cefotaxime, ceftriaxone, imipenem-cilastatin, penicillin G, moxifloxacin, ciprofloxacin, and levofloxacin had MIC(90)s between 0.030 and 0.125 microg/ml. Doxycycline and tetracycline had the highest MIC(90)s: 2 and 4 microg/ml, respectively. Doxycycline and tetracycline were noted to have slightly higher MICs against isolates from Egypt than against strains from Thailand or Hawaii; otherwise, the susceptibility patterns were similar. There appears to be possible variability in susceptibility to some antimicrobial agents among strains, suggesting that more extensive testing to look for geographic variability should be pursued.