Leishmania donovani in hamsters: Stimulation of non-specific resistance by novel lipopeptides and their effect in antileishmanial therapy

Several novel type of lipopeptides were synthesized and evaluated for their ability to stimulate non-specific resistance againstLeishmania donovani infection. Peritoneal macrophages isolated from young male hamsters treated with muramyl dipeptide (MDP) and various synthetic lipopeptides (6 mg/kg i.p.) 7 days earlier, were cultured in vitro and challenged 24 h later withL. donovani promastigotes. One lipopeptide, Central Drug Research Institute (CDRI) compound 86/450, exhibited significantly higher immunostimulatory activity than MDP. Its prophylactic activity was further confirmed in hamsters by giving 2 split doses of 3 mg/kg of the compound spaced at 2 weeks, i.e. on day –7 and +7 of challenge withL. donovani amastigotes. The prophylactic effect lasted for 7 days following the last treatment with compound 86/450. The antileishmanial action of sodium stibogluconate (SAG) was also found to be enhanced by 16% in hamsters primed with compound 86/450.CDRI Communication No. 5034.     

Leishmania donovani in hamsters: stimulation of non-specific resistance by some novel glycopeptides and impact on therapeutic efficacy

Several glycopeptides structurally related to muramyl dipeptide (MDP) have been synthesized and evaluated for their ability to stimulate the non-specific resistance of hamsters against L. donovani infection. These compounds have been named CDRI compounds. The synthetic procedure used for compounds 86/448 and 84/212 is described. MDP and its synthetic congeners were administered as immunostimulants at a prophylactic dose of 3 mg/kg at two weeks interval. The challenge infection (1 x 10(7) amastigotes i.c./hamster) was given in between two doses of the compounds. One of the glycopeptides, CDRI comp. 86/448, has been found to be significantly more potent than MDP, effecting 92% inhibition of the challenge dose, whereas MDP produced only 26.5% inhibition. The effect of comp. 86/448 lasted until day 7 of challenge. The efficacy of sodium stibogluconate was appreciably improved in hamsters treated with comp. 86/448.     

Genetics of toxin production and resistance in phytopathogenic bacteria

Genes for phytotoxin production have been identified and cloned from several phytopathogenic pseudomonads. These genes comprise physically linked clusters that have been located both on the chromosome and on endogenous plasmids. Contained within these genetic regions are resistance genes specific to those toxins that have a bactericidal component to their activity. DNA sequences required for toxin production are often conserved among bacteria with divergent host specificities, suggesting the ability of toxin genes to be transferred between bacteria. Toxins are usually modulators of plant pathogenicity, their production causing a significant increase in disease severity. In one case, however, toxin production appears to be a major contributor to the basic pathogenicity of a plant pathogenic bacterium.     

Antimalarial drugs: recent advances in molecular determinants of resistance and their clinical significance

Molecular determinants of antimalarial drug resistance are useful and informative tools that complement phenotypic assays for drug resistance. They also guide the design of strategies to circumvent such resistance once it has reached levels of clinical significance. Established resistance to arylaminoalcohols such as mefloquine and lumefantrine in SE Asia is mediated primarily by gene amplification of the P. falciparum drug transporter, pfmdr1. Single nucleotide polymorphisms in pfmdr1, whether assessed in field isolates or transfection experiments, are associated with changes in IC₅₀ values (to arylaminoalcohols and chloroquine), but not of such magnitude as to influence clinical treatment outcomes. Recently described emerging in vitro resistance to artemisinins in certain areas correlates with mutations in the SERCA-like sequence PfATP6 and supports PfATP6 as a key target for artemisinins. Received 13 February 2006; revised after revision 7 March 2006; accepted 29 March 2006     

Effects of diapause and host species on some morphometric characters inTrichogramma (Hym.: Trichogrammatidae)

Adult morphology ofTrichogramma is modified by environmental conditions during the preimaginal development. For instance, the low temperatures inducing diapause cause a decrease of the ratio length of longest seta on male flagellum/width of flagellum inT. evanescens. The species of the host also influences numerous body ratios. So, in females, the development of tibiae with regard to wings is more important withScotia ipsilon than withGalleria mellonella. These results confirm the necessity of performing comparative morphological studies on individuals reared in the same conditions.     

Extra-nuclear inheritance in a sexually produced aphid: the ability to overcome host plant resistance by biotype hybrids of the greenbug,Schizaphis graminum

Summary Greenbugs of biotype E that grow and reproduce well on a biotype C-resistant sorghum (IS 809) were crossed with biotype C greenbugs. The resulting hybrids were tested on IS 809 to study how the ability to overcome the cultivar's resistance is inherited. Only those hybrids stemming from biotype E mothers were able to overcome the resistance of IS 809 plants, indicating that this trait is inherited by the sexually-produced fundatrices in an extra-nuclear manner from the mother. A plausible explanation for this phenomenon is presented.     

Induction of cyst formation by low temperature in the dinoflagellateGonyaulax polyedra Stein: Dependence on circadian phase and requirement of light

Encystment, which at a temperature of 15°C is photoperiodically controlled inGonyaulax polyedra, can also be induced by a decrease of temperature, from 20 to 10 or 8°C in the absence of photoperiodic signals. The cyst-inducing capacity of the decrease in temperature depends on the circadian phase: in constant light, the maximum of sensitivity was found at the beginning of subjective night. In a light/dark cycle, however, cyst formation was reduced during dark phase, indicating that light is required for the process of encystment. A similar light dependence was seen in the effect of the physiologically occurring cyst inducer 5-methoxytryptamine, but not in the encystment response to the protonophores monensin and nigericin.     

A simple method for in vivo testing of glandular enzymatic activity on potential precursors of larval defensive compounds inPhratora species (Coleoptera: Chrysomelinae)

The presence of glandular -glucosidase and oxidase-specific activities, and the possible role of phenolglucosides and related compounds as precursors for larval defensive compounds, were directly demonstrated by introducing salicin, saligenin and helicin into the defensive glands ofPhratora species.Ph. tibialis andPh. laticollis that normally secrete endogenously-produced iridoid monoterpenes and do not use phenolglucosides from their food sources as precursors, were able to produce salicyladehyde from helicin when the latter was introduced into the defensive glands.