Inhibiting scrapie neuroinvasion by polyene antibiotic treatment of SCID mice.
(41/2502)
The polyene antibiotic MS-8209 is currently one of the most effective drugs in the treatment of experimental scrapie. However, its mechanism of action and its site of intervention in the pathogenetical process of scrapie infection are largely unknown. It has been shown previously that the infection of immunodeficient SCID mice by the peripheral route provides a reliable model for direct scrapie neuroinvasion, bypassing the lymphoreticular system. Indeed, a proportion of SCID mice develop scrapie after a similar time to immunocompetent mice, despite their severe immune impairment. This model is now used to clarify the targets of MS-8209. In SCID mice, MS-8209 treatment protected against infection but did not prolong survival time. In SCID mice immunologically reconstituted prior to inoculation, the drug delayed the disease without an effect on the attack rate. These findings strongly suggest that MS-8209 acts by hampering the first step of the neuroinvasion process, i.e. the uptake of the infectious agent by peripheral nerve endings. The mechanism leading to the inhibition of agent propagation to nervous cells is discussed with regard to the properties of polyene antibiotics. (+info)
Nystatin effects on vacuolar function in Saccharomyces cerevisiae.
(42/2502)
The effects of nystatin, a polyene antibiotic, was studied in Saccharomyces cerevisiae by isolating and characterizing nystatin-sensitive mutants. We isolated a number of nystatin-sensitive mutants by ethylmethane sulfonate mutagenesis. One of these mutants, the nss1 mutant, was characterized in detail. The mutant was sensitive to stresses such as high temperature or high concentrations of monovalent and divalent cations. The nss1 mutants showed severe vacuolar protein sorting and vacuolar morphology defects. The nss1 mutant was demonstrated to have a mutational lesion in the known VPS16 gene, which is essential for vacuolar protein sorting in S. cerevisiae. All of the vacuolar deficient mutants (vps11, vps16, vps18, and vps33) were sensitive to nystatin. Nystatin was found to cause extensive enlargement of the vacuole in wild-type S. cerevisiae cells. These results are discussed with special reference to the vacuolar function of S. cerevisiae. (+info)
Heteroresistance to fluconazole and voriconazole in Cryptococcus neoformans.
(43/2502)
Cryptococcus neoformans isolates that exhibited unusual patterns of resistance to fluconazole and voriconazole were isolated from seven isolates from two different geographical regions: one isolate from an Israeli non-AIDS patient and six serial isolates from an Italian AIDS patient who had suffered six recurrent episodes of cryptococcal meningitis. Each isolate produced cultures with heterogeneous compositions in which most of the cells were susceptible, but cells highly resistant to fluconazole (MICs, >/=64 microg/ml) were recovered at a variable frequency (7 x 10(-3) to 4.6 x 10(-2)). Evidence showed that this type of resistance is innate and is unrelated to drug exposure since the Israeli patient had never been treated with azoles or any other antimycotic agents. Analysis of clonal subpopulations of these two strains showed that they exhibited heterogeneous patterns of resistance. The number of subpopulations which grew on fluconazole or voriconazole agar declined progressively with increasing azole concentration without a sharp cutoff point. For the Italian serial isolates, the number of clonal populations resistant to fluconazole (64 microg/ml) and voriconazole (1 microg/ml) increased steadily, yielding the highest number for the isolate from the last episode. Attempts to purify a sensitive subpopulation failed, but clones highly resistant to fluconazole (100 microg/ml) and moderately resistant to voriconazole (1 microg/ml) always produced a homogeneous population of resistant cells. Upon maintenance on drug-free medium, however, the majority of the homogeneously resistant cells of these subclones lost their resistance and returned to the stable initial heteroresistant phenotype. The pattern of heteroresistance was not affected by the pH or osmolarity of the medium but was influenced by temperature. The resistance appeared to be suppressed at 35 degrees C and was completely abolished at 40 degrees C. Although heterogeneity in azole resistance among subpopulations of single isolates has been reported for Candida species, the transient changes in expression of resistance under different growth conditions reported here have not been observed in fungal pathogens. (+info)
A novel injectable water-soluble amphotericin B-arabinogalactan conjugate.
(44/2502)
New, stable, highly water-soluble, nontoxic polysaccharide conjugates of amphotericin B (AmB) are described. AmB was conjugated by a Schiff-base reaction with oxidized arabinogalactan (AG). AG is a highly branched natural polysaccharide with unusual water solubility (70% in water). A high yield of active AmB was obtained with the conjugates which were similarly highly water soluble and which could be appropriately formulated for injection. They showed comparable MICs for Candida albicans and Cryptococcus neoformans (MICs, 0.1 to 0.2 microg/ml). The reduced AmB conjugate, which was synthesized at pH 11 for 48 h at 37 degrees C, was nonhemolytic and was much safer than conventional micellar AmB-deoxycholate. It was the least toxic AmB-AG conjugate among those tested with mice (maximal tolerated dose, 50 mg/kg of body weight), and histopathology indicated no damage to the liver or kidneys. This conjugate, similarly to the liposomal formulation (AmBisome), was more effective than AmB-deoxycholate in prolonging survival. It was more effective than both the liposomal and the deoxycholate formulations in eradicating yeast cells from target organs. The overall results suggest that after further development of the AmB-AG conjugate, it may be a potent agent in the treatment of fungal infections. (+info)
Diagnostic PCR with Leishmania donovani specificity using sequences from the variable region of kinetoplast minicircle DNA.
(45/2502)
Kala azar or visceral leishmaniasis, a parasitic disease caused by Leishmania donovani, is presently causing an epidemic in the eastern region of India. Diagnosis of kala azar is often complicated. We developed a pair of oligonucleotides suitable as primers from the variable region of a predominant sequence class of minicircles of L. donovani. These primers were used in a nonisotopic polymerase chain reaction and found to be highly specific for the parasites of L. donovani complex. Using these primers, amplification of L. donovani kinetoplast DNA minicircle from the peripheral blood of kala azar patients results in a product of 204 bp. The patient group was comprised of individuals from a highly endemic region of India. We feel that PCR could assess the efficacy of new leishmanicidal drugs under investigation in these patients. PCR could also predict response to therapy which would be useful for both clinical and research applications. (+info)
Optimizing voriconazole susceptibility testing of Candida: effects of incubation time, endpoint rule, species of Candida, and level of fluconazole susceptibility.
(46/2502)
Voriconazole is a new triazole antifungal agent that has potent activity against many isolates of Candida, including Candida krusei and Candida glabrata. In this work, we studied the impact of glucose supplementation, incubation time, agitation of the plates prior to reading, endpoint determination rule, visual versus spectrophotometric reading, Candida species, and fluconazole MIC on the MIC of voriconazole for Candida isolates tested by using the microdilution format assay of the National Committee for Clinical Laboratory Standards (NCCLS) M27-A antifungal susceptibility testing methodology. For both voriconazole and fluconazole, a spectrophotometric endpoint of 50% reduction in turbidity relative to the growth control correlated most closely with the NCCLS-defined visual endpoint of "prominent decrease in turbidity." Correlation was generally better after 24 h of incubation than after 48 h. Supplementation of the medium to contain 20 g of glucose/liter did not alter the MIC significantly but did enhance growth and simplify visual readings. All Candida species appeared potentially susceptible to voriconazole, including isolates of C. krusei. For some isolates for which fluconazole MICs were markedly elevated voriconazole MICs were also elevated, but the clinical significance of these observations remains to be determined. (+info)
Visceral leishmaniasis in renal transplant recipients: successful treatment with liposomal amphotericin B (AmBisome).
(47/2502)
Visceral leishmaniasis (VL) is a rare disease in renal transplant recipients. Liposomal amphotericin B (AmBisome) is known to be effective against VL. However, previously there has been no experience with administration of such treatment to renal transplant recipients. We report herein four patients with VL complicating renal transplantation who were treated successfully with liposomal amphotericin B (total dose, 23-40 mg/kg). Neither adverse reactions nor clinical relapses of VL were observed. (+info)
Flow cytometric assessment of amphotericin B susceptibility in Leishmania infantum isolates from patients with visceral leishmaniasis.
(48/2502)
Amphotericin B susceptibility was measured by a flow cytometric membrane potential assay in Leishmania infantum promastigotes isolated from 11 immunocompetent children treated with liposomal amphotericin B and 19 HIV-infected young adults treated with intralipid amphotericin B. Susceptibility levels were measured by the 90% inhibitory concentrations (IC90) representing the concentrations of drug that induced a 90% decrease in membrane potential compared with the control culture. In immunocompetent children, treatment was fully effective whatever the susceptibility of isolates to amphotericin B. In immunocompromised adults, on the contrary, unresponsiveness and relapses could be observed in all cases and IC90 increased in the course of successive treatments: a decrease of amphotericin B susceptibility in both promastigote and amastigote forms could be observed in a patient who had six relapses. These results suggest that the success of amphotericin B treatment depends greatly on patient immunity status, and indicate that successive relapses could enhance emergence of amphotericin B resistant isolates. The results demonstrate that the flow cytometric membrane potential assay can be used as an easy and reliable tool for studying the evolution of interactions between amphotericin B and the parasite membrane during long-term treatments. (+info)