Antagonistic Effect of Bacteria Isolated from the Digestive Tract of Lutzomyia evansi against Promastigotes of Leishmania infantum, Antimicrobial Activities and Susceptibility to Antibiotics

Lutzomyia evansi is a phlebotomine insect endemic to Colombia’s Caribbean coast and is considered the main vector of visceral and cutaneous leishmaniasis in the region. Specific studies of the direct effects generated by bacteria in the digestive tract of the insect vectors, under Leishmania infantum using in vitro models, represent a novel alternative as a control strategy for the transmission of leishmaniasis and also provide the opportunity to detect natural products or antimicrobial peptides with different biological activities. In this study, we evaluate the leishmanicidal and antimicrobial activities of Pantoea ananatis, Ochrobactrum anthropi and Enterobacter cloacae, isolated from the digestive tract of Lutzomyia evansi and the susceptibility of these bacteria to commonly used antibiotics. The antagonistic effect of Pantoea ananatis, Ochrobactrum anthropi and Enterobacter cloacae was evaluated against six species of human pathogenic bacteria and against stationary (Metacyclic-like) and exponential promastigotes (Procyclic-like) of Leishmania infantum (BCN-GFP strain) by co-culture assays for 24 hours. The activity of the bacterial isolates on Leishmania infantum promastigotes was quantified by flow cytometry. The susceptibility of the bacterial strains to clinically used antibiotics was analyzed by antibiogram. The highest percentage of inhibition was observed against exponential promastigotes with bacterial concentrations of 108 CFU/ml of Enterobacter cloacae (77.29% ± 0.6%) and Pantoea ananatis (70.17% ± 1.1%). The extracts produced by three bacterial isolates showed similar biological activity (13 mm - 22 mm inhibition halos) against all tested bacteria;however, significant differences were observed with respect to gram-positive bacteria (P < 0.003557). The most active antibacterial activity was displayed against the pathogenic bacteria Bacillus cereus. Ochrobactrum anthropi was the isolate with the highest number of antibiotic resistance patterns while Pantoea ananatis and Enterobacter cloacae showed greater susceptibility to the evaluated antibiotics. The growth inhibitory activity of exponential Leishmania infantum promastigotes shown by extracts of Enterobacter cloacae and Pantoea ananantis suggests that the presence of these bacteria in the vector intestine may affect the parasite development to metacyclic stages, infective to human hosts. This in turn confers said bacteria, a potential in controlling the transmission of Leishmania spp. that deserves to be studied in depth.

In vitro antileishmanial effects of Physalis angulata root extract on Leishmania infantum

Objective： In the present study, we evaluated the effects of the aqueous extract of Physalis angulata root （AEPa） on Leishmania infanturn proliferation, morphology, and the driving mechanism in leishmanicidal activity and modulatory action on macrophages. Methods： I., infantum promastigotes were treated with 50 and 100 μg/mL AEPa for 72 h and then antipro- mastigote assay was performed by counts in a Newbauer chamber, morphological changes were analyzed by transmission electron microscopy and the mechanism of the leishmanicidal activity was detected. In addition, macrophages were infected with L. infantum and were used to evaluate anti-amastigote activity of AEPa and effects of AEPa on cytokine secretion after 72-hour treatment. Results： Treatment with AEPa reduced the numbers ofL infantum promastigotes （50% inhibitory concen- tration （ICso） = 65.9μg/mL; selectivity index （SI）= 22.1） and amastigotes （ICso = 37.9 μg/mL; SI = 38.5） compared with the untreated control. Amphotericin B reduced 100% of the promastigote numbers after 72 h of treatment （IC50 = 0.2μg/mL）. AEPa induced several morphological changes and increased the production of reactive oxygen species and apoptotic death in promastigotes after treating for 72 h. AEPa （100 μg/mL） promoted tumor necrosis factor-α secretion in macrophages infected with L. infantum after 72 h of treatment, but did not induce an increase in this cytokine in noninfected macrophages. In addition, AEPa showed no cytotoxic effect on J774-A1 cells （50% cytotoxic concentration 〉1000μg/mL）. Conclusion： AEPa presented antileishmanial activity against the promastigotes and amastigotes of I.. infantum without macrophage cytotoxicity; these results show that natural products such as P. angulata have leishmanicidal potential and in the future may be an alternative treatment for leishmaniasis.