Parasitological and molecular search for Leishmania natural infection in phlebotomine sand flies in peri-urban and rural sites of an Argentinean area endemic for tegumentary leishmaniasis

Leishmaniases are neglected tropical diseases caused by Leishmania spp. parasites transmitted by the bite of phlebotomine sand flies. In Argentina, the most endemic area of American tegumentary leishmaniasis (ATL) has been Orán department, Province of Salta, where Leishmania (Viannia) braziliensis prevails and Nyssomyia neivai is considered as its vector, although there is no accurate and sufficient information in this regard. The aim of this work was to search for natural infection by Leishmania spp. in sand flies from peri-urban and rural sites with ATL background in Orán department. For this, sand flies were caught at five sites; female sand flies captured with Shannon trap were dissected to microscopically examine their gut contents, while females captured with CDC traps were molecularly analyzed by duplex PCR with two primer pairs to simultaneously amplify kinetoplast DNA (kDNA) and mammalian actin. A total of 1921 females were captured, with Ny. neivai being the most abundant species (89%), followed by Migonemyia migonei (6%) and cortelezzii complex (3%). No natural infection was found in any of them neither by dissection nor by PCR, although the detection limit of kDNA PCR was up to 25 promastigotes. The absence of infected females in peri-urban sites suggest that the transmission did not take place in those environments during the study period. Future searches for natural infection should focus on rural settings to deepen knowledge and elucidate the role of the circulating sand fly species as all have been linked to ATL transmission at other sites.

Development of a Fluorescent Assay to Search New Drugs Using Stable tdTomato-Leishmania, and the Selection of Galangin as a Candidate With Anti-Leishmanial Activity

Antimonials continue to be considered the first-line treatment for leishmaniases, but its use entails a wide range of side effects and serious reactions. The search of new drugs requires the development of methods more sensitive and faster than the conventional ones. We developed and validated a fluorescence assay based in the expression of tdTomato protein by Leishmania, and we applied this method to evaluate the activity in vitro of flavonoids and reference drugs. The pIR1SAT/tdTomato was constructed and integrated into the genome of Leishmania (Leishmania) amazonensis. Parasites were selected with nourseothricin (NTC). The relation of L. amaz/tc3 fluorescence and the number of parasites was determined; then the growth in vitro and infectivity in BALB/c mice was characterized. To validate the fluorescence assay, the efficacy of miltefosine and meglumine antimoniate was compared with the conventional methods. After that, the method was used to assess in vitro the activity of flavonoids; and the mechanism of action of the most active compound was evaluated by transmission electron microscopy and ELISA. A linear correlation was observed between the emission of fluorescence of L. amaz/tc3 and the number of parasites (r2 = 0.98), and the fluorescence was stable in the absence of NTC. No differences were observed in terms of infectivity between L. amaz/tc3 and wild strain. The efficacy of miltefosine and meglumine antimoniate determined by the fluorescence assay and the microscopic test showed no differences, however, in vivo the fluorescence assay was more sensitive than limiting dilution assay. Screening assay revealed that the flavonoid galangin (GAL) was the most active compound with IC50 values of 53.09 µM and 20.59 µM in promastigotes and intracellular amastigotes, respectively. Furthermore, GAL induced mitochondrial swelling, lipid inclusion bodies and vacuolization in promastigotes; and up-modulated the production of IL-12 p70 in infected macrophages. The fluorescence assay is a useful tool to assess the anti-leishmanial activity of new compounds. However, the assay has some limitations in the macrophage-amastigote model that might be related with an interfere of flavanol aglycones with the fluorescence readout of tdTomato. Finally, GAL is a promising candidate for the development of new treatment against the leishmaniasis.

Sand fly typing: a simple and morphologically-supported method based on polymorphism of 18S rRNA gene in a Leishmaniasis endemic area of Argentina

Leishmaniases are vector-borne diseases that in the Americas are distributed from southern United States to northern Argentina. The vectors for this disease are small dipterans known as sand flies that are usually identified morphologically by observing structures with taxonomic value; but it is time-consuming, laborious, and requires entomological expertise. Then, this work was aimed at identifying sand flies with molecular techniques, using the morphological identification as a reference technique, in an endemic area of American Tegumentary Leishmaniasis (ATL) located in northern Argentina. For this, sand flies were caught at two patches of vegetation adjacent to rural areas in Orán department, Salta Province. Females were dissected with sterile needles; the head and last abdominal segments were analyzed for morphological identification. The remaining thorax and abdominal segments were used to extract DNA, which was amplified by PCR of the small subunit (SSU), 18S rRNA gene. PCR products were digested with CviQI and DdeI enzymes to identify sand fly species by Restriction Fragment Length Polymorphism (RFLP) analysis. Thus, the restriction pattern of each caught species was defined according to morphological identification. A total of 1501 females, belonging to four sand fly species, were captured. Nyssomyia neivai (1347/1501) was the most abundant species, followed by Migonemyia migonei (90/1501). From the total, 801 females were morphologically and molecularly identified, while 700 females were characterized only molecularly. For those females analyzed by both methods, there was total coincidence in the achieved result. Besides, the 5% (38/801) of females that could not be determined morphologically due to inadequate mounting were molecularly identified. All the females characterized just by PCR-RFLP, were successfully identified. Our results indicate that the explored method is capable of identifying the sand fly species that circulate in an ATL endemic area. Since this method is based on the analysis of markedly different patterns, the identification process might be more easily reproduced, as the bias introduced by the technician's lack of experience is removed.

Development of a Multilocus sequence typing (MLST) scheme for Pan-Leishmania

Since the description of the Leishmania genus, its identification and organization have been a challenge. A high number of molecular markers have been developed to resolve phylogenetic differences at the species level and for addressing key epidemiological and population genetics questions. Based on Multilocus enzyme electrophoresis (MLEE), Multilocus sequence typing (MLST) schemes have been developed using different gene candidates. From 38 original gene targets proposed by other authors, 27 of them were chosen. In silico selection was made by analyzing free access genomic sequence data of 33 Leishmania species, one Paraleishmania representative, and one outgroup, in order to select the best 15 loci. De novo amplifications and primers redesign of these 15 genes were analyzed over a panel of 20 reference strains and isolates. Phylogenetic analysis was made at every step. Two MLST schemes were selected. The first one was based on the analysis of three-gene fragments, and it is suitable for species assignment as well as basic phylogenetic studies. By the addition of seven-genes, an approach based on the analysis of ten-gene fragments was also proposed. This is the first work that two optimized MLST schemes have been suggested, validated against a phylogenetically diverse panel of Leishmania isolates. MLST is potentially a powerful phylogenetic approach, and most probably the new gold standard for Leishmania spp. characterization.

Lutzomyia longipalpis (Diptera: Psychodidae) Argentina-Bolivia border: new report and genetic diversity

American visceral leishmaniasis (AVL) has two main scenarios of transmission as follows: scattered cases in rural areas and urban outbreaks. Urban AVL is in active dispersion from the northeastern border of Argentina-Paraguay-Brazil to the South. The presence of Lutzomyia longipalpis was initially reported in urban environments in the northwestern border of the country. The presence of Lu. longipalpis, environmental variables associated with its distribution, and its genetic diversity were assessed in Salvador Mazza, Argentina, on the border with Bolivia. The genetic analysis showed high haplotype diversity, low nucleotide diversity, and low nucleotide polymorphism index. We discuss the hypothesis of an expanding urban population with introgressive hybridisation of older haplogroups found in their path in natural forest or rural environments, acquiring a new adaptability to urban environments, and the possibility of changes in vector capacity.

Molecular Identification of Leishmania spp. DNA from Archived Giemsa-Stained Slides of Patients from Salta, Argentina

Cutaneous leishmaniasis is endemic in Salta province, which belongs to the northwest of Argentina. Leishmania spp. DNA from Giemsa-stained slides of up to 12 years in storage of patients from Salta was characterized through polymerase chain reaction (PCR) restriction fragment length polymorphism (RFLP). One hundred smears positive for microscopy, classified in a semiquantitative scale for amastigote density, were analyzed. Also, Leishmanin skin test (LST) results were included. DNA extraction was carried out applying lysis buffer with proteinase K, and then DNA was amplified with ribosomal internal transcribed spacer 1 primers. PCR products were digested with HaeIII enzyme. All PCR-positive smears (74/100) belonged to Viannia subgenus. A statistically significant, directly proportional relationship between semiquantitative microscopy and PCR results was detected. All patients had LST-positive results (induration ≥ 5 mm), and the smears of those with smaller induration (LST < 19 mm) gave a higher proportion of positive PCR results. This study determined that smear age did not affect PCR positivity, which allows retrospective analyzes and suggests smears might be useful for molecular complementary diagnosis. Because Leishmania (Viannia) braziliensis is the main circulating species in the study area, determining Viannia subgenus in all analyzed samples confirms previous findings. PCR positivity showed statistically significant differences according to semiquantitative microscopy, highlighting the importance of parasite burden in the diagnostic sensitivity of the method. Considering that smears of patients with smaller LST induration were more positive in PCR, a negative smear from patients with positive LST response, but < 19 mm, could actually represent a false-negative result.

Characterization and genetic diversity of pepper (Capsicum spp) parents and interspecific hybrids

Pepper species exhibit broad genetic diversity, which enables their use in breeding programs. The objective of this study was to characterize the diversity between the parents of different species and their interspecific hybrids using morphological and molecular markers. The parents of Capsicum annuum (UFPB-01 and -137), C. baccatum (UFPB-72), and C. chinense (UFPB-128) and their interspecific hybrids (01x128, 72x128, and 137x128) were used for morphological and molecular characterization. Fruit length and seed yield per fruit (SYF) traits showed the highest variability, and three groups were formed based on these data. CVg/CVe ratio values (>1.0) were calculated for leaf length (1.67) and SYF (5.34). The trait that most contributed to divergence was the largest fruit diameter (26.42%), and the trait that least contributed was pericarp thickness (0.33%), which was subject to being discarded. The 17 primers produced 58 polymorphic bands that enabled the estimation of genetic diversity between parents and hybrids, and these results confirmed the results of the morphological data analyses. The principal component analysis results also corroborated the morphological and random-amplified polymorphic DNA data, and three groups that contained the same individuals were identified. These results confirmed reports in the literature regarding the phylogenetic relationships of the species used as parents, which demonstrated that C. annuum was closer to C. chinense as compared to C. baccatum.

Embryogenesis in the anthers of different ornamental pepper (Capsicum annuum L.) genotypes

The aim of this study was to relate flower bud size with microspore developmental stages and the induction of embryos in the anthers of different ornamental pepper (Capsicum annuum L.) genotypes. Flower buds were randomly collected and visually divided into three classes based on both petal and sepal size. The length and diameter of the bud as well as the length of the petal, sepal, and anther were then measured. The microspore stage was also determined for each anther of the bud where it was found. The data were subjected to analysis of variance (P ≤ 0.01), and the means were separated by Tukey's test (P ≤ 0.01). The broad sense heritability, the CVg/CVe relation, and the Pearson correlation between characters were also determined. Anthers from 10 C. annuum genotypes were cultivated in four culture media types for the induction of embryos. The data were transformed by Arcsin (x) and subjected to analysis of variance (P ≤ 0.01), and the means were separated by Tukey's test (P ≤ 0.01). The majority of anthers in the second class had uninucleate microspores. No correlation was observed between bud size and the number of uninucleate microspores. Genotype 9 specimens grown in M2 medium induced the highest number of embryos (16) compared to the other treatments, which indicates a significant interaction effect between culture media and genotypes.

The identification of sandfly species, from an area of Argentina with endemic leishmaniasis, by the PCR-based analysis of the gene coding for 18S ribosomal RNA

The area around Río Blanco, in the Orán department in the north of the Argentinian province of Salta, is endemic for American tegumentary leishmaniasis. In an attempt to facilitate the identification of the Lutzomyia species in this area, sequences of the gene coding for the 18S ribosomal RNA (rRNA) of sandflies caught in a Shannon trap were explored, by a combination of PCR and analysis of restriction-fragment-length polymorphism (RFLP). The products from the PCR, which employed two primers developed specifically for this study (Lu.18S 1S and Lu.18S AR), were cloned into a commercial vector (pGEM-T Easy) so that their nucleotide sequences could be investigated. In the RFLP analysis, the products of single and double digestion with the AfaI and HapII restriction enzymes were separated by electrophoresis in 3% or 4% agarose. Taken together with the results of a morphological investigation of the flies, the resultant DNA fragment patterns were sufficient to identify most of the sandflies caught as Lu. neivai. Although two other species, Lu. cortelezzii and Lu. sallesi, were collected, they were relatively rare and only identified morphologically. A single digestion of the 18S-rRNA gene sequences with AfaI or HapII appeared sufficient and useful for the identification of Lu. neivai from the north of Salta province, and for several other Lutzomyia species.

A trial of immunotherapy against Leishmania amazonensis infection in vitro and in vivo with Z-100, a polysaccharide obtained from Mycobacterium tuberculosis, alone or combined with meglumine antimoniate

OBJECTIVES

To determine the efficacy and the immunomodulatory function of Z-100 alone or combined with meglumine antimoniate on Leishmania amazonensis infection.

METHODS

The effect of the compounds was evaluated by microscopic counting of intracellular amastigotes in macrophages stained with Giemsa, or axenic promastigotes, and IC(50) was determined by linear regression. The antileishmanial effect of the compounds was assessed in infected BALB/c mice by a limiting dilution analysis and the production of gamma interferon (IFN-gamma), interleukin 10 (IL-10), IL-4, IgG1 and IgG2a was measured by ELISA.

RESULTS

In vitro, Z-100 showed antileishmanial activity against intracellular amastigotes of L. amazonensis with an IC(50) of 13 mg/L. Moreover, infected macrophages treated with Z-100 (12 mg/L) showed smaller parasitophorous vacuoles with fewer parasites than the control. In addition, the efficacy of Z-100 plus meglumine antimoniate [14 mg/L pentavalent antimony (Sb(v))] was higher (46% inhibition) than either Z-100 or meglumine antimoniate alone. Nevertheless, no effect of Z-100 on axenic promastigotes was observed. Infected BALB/c mice treated with Z-100 (100 microg/kg) alone did not show any antileishmanial effects in comparison with the control group, and IFN-gamma, as well as IL-10 and IL-4, was up-regulated by the treatment. In addition, both IgG1 and IgG2a were also increased by the Z-100 treatment. Although Z-100 plus meglumine antimoniate (14 or 28 mg/kg Sb(v)) controlled both the parasite load and the footpad swelling in comparison with control mice, no significant differences were found with meglumine antimoniate alone.

CONCLUSIONS

In vitro, Z-100 alone or combined with meglumine antimoniate showed an antileishmanial effect on L. amazonensis. However, no effect was observed in infected BALB/c mice treated with Z-100, suggesting that the up-regulation of IL-10 and IL-4 production by the treatment could be interfering with the development of a protective Th1-type response. For further understanding of the effects of Z-100 in vivo, another strain of mice such as C57BL/6 should be tested in future.

Variability and interactions between endophytic bacteria and fungi isolated from leaf tissues of citrus rootstocks

Fungi and bacteria were isolated from surface disinfected leaf tissues of several citrus rootstocks. The principal bacterial species isolated were Alcaligenes sp., Bacillus spp. (including B. cereus, B. lentus, B. megaterium, B. pumilus, and B. subtilis), Burkholderia cepacia, Curtobacterium flaccumfaciens, Enterobacter cloacae, Methylobacterium extorquens, and Pantoea agglomerans, with P. agglomerans and B. pumilus being the most frequently isolated species. The most abundant fungal species were Colletotrichum gloeosporioides, Guignardia citricarpa, and Cladosporium sp. Genetic variability between 36 endophytic bacterial isolates was analysed by the random amplified polymorphic DNA (RAPD) technique, which indicated that B. pumilus isolates were more diverse than P. agglomerans isolates, although genetic diversity was not related to the host plants. In vitro interaction studies between G. citricarpa isolates and the most frequently isolated endophytic bacteria showed that metabolites secreted by G. citricarpa have an inhibitory growth effect on some Bacillus species, and a stimulatory growth effect on P. agglomerans.