Semiconductor quantized voltage source.

We realize and investigate an all-semiconductor quantized voltage source which generates quantized output voltages V(out) = f(h/e) linked only to two fundamental constants, the electron's charge e and Planck's constant h, and to an applied excitation frequency f. The device is based on an integrated quantized circuit of a single-electron pump operated at pumping frequency f and a quantum Hall device monolithically integrated in series. Robust output voltages up to several µV are generated, which are expected to be scalable by orders of magnitude using present technology. The device might open a new route towards the closure of the quantum metrology triangle.

An improved method for the prolonged maintenance of Pneumocystis carinii in vitro.

A culture system for rat-derived Pneumocystis carinii was developed that allows the long-term maintenance of viable organisms in vitro. Organisms were derived from the lungs of immunosuppressed rats infected with P. carinii. P. carinii was maintained in culture with human embryonal lung (HEL) fibroblasts and Eagle MEM for up to 42 days. Passage of organisms was done by reinoculation of infected HEL cells with attached P. carinii onto a fresh monolayer of confluent cells. Rats pretreated with trimethoprim-sulfamethoxazole and inoculated with cultured organisms (up to day 42) developed P. carinii pneumonia by 6 weeks while control animals remained uninfected. P. carinii was able to be harvested from these lungs and reintroduced into tissue culture. Cultures have been maintained for up to 6 weeks without a substantial loss of P. carinii viability. In combination with intratracheal inoculation, this system raises the possibility of maintaining stable laboratory strains of P. carinii.

Cloning of a fresh isolate of Plasmodium falciparum and drug sensitivity of the clones.

A freshly isolated strain of Plasmodium falciparum was cloned by limited dilution using a co-culture of infected erythrocytes on monolayers of functionally active rodent hepatocytes. 15 clones were isolated, and the anti-malarial activity of chloroquine, quinine, mefloquine and halofantrine against the clones, the original isolate, and a culture-adapted isolate was determined using a 48 h radioisotope microdilution method. The multiplication rates of all clones and the culture-adapted isolate were estimated by counting the number of parasitized cells on Giemsa-stained thin smears. Variations found in drug sensitivity and multiplication rate of different clones provided strong evidence of heterogeneity of a single strain parasite population. No morphological variation was detected by light microscopy. The use of a hepatocyte feeder layer improved the adaptation of cloned parasites to continuous culture conditions and thus enabled us to clone directly a fresh isolate, without losing clones during the culture-adaptation process.

Continuous culture of Plasmodium falciparum asexual stages in "normal" air atmosphere.

The growth of six strains of Plasmodium falciparum in 5% CO2, 5% O2, 90% N2 and normal air atmosphere was determined daily by microscopical examination of blood films. All strains were able to grow in flasks without additional gas mixture but significantly lower parasitaemia was observed within the first five days of cultivation. Attempt at cultivating in petri dishes without candle jar technique failed but parasites survived in plasticine sealed dishes. The cultivation in air cannot be recommended for cultures initiated from cryopreserved material or low parasitaemia (0.1-0.3%) cultures.

Serological diagnostics of imported malaria in Czechoslovakia.

Two serologic techniques for malaria detection were compared in this study; the indirect fluorescent antibody (IFA) test used in 214 persons (38 Czechoslovak citizens returning from visits to tropical countries and 176 foreign visitors arriving to Czechoslovakia from areas endemic for malaria) and the indirect hemagglutination (IHA) test employed in 125 persons (29 Czechoslovak citizens and 96 foreigners). Comparisons revealed poor correlation between the IFA test and IHA test data. Of the two tests the IFA test appeared to be distinctly more reliable, more sensitive and more specific, the IHA test turned out to yield both false positive and false negative results. The antigen from Plasmodium gallinaceum gave lower IFA titres than P. falciparum antigen, but reacted with antibodies to all species of human plasmodia, and gave reliable test results. Positive serologic responses were appreciably more frequent in foreigners (46.0%) than Czechoslovak citizens (23.7%). The maximum percent positivity for malarial antibody was among individuals from tropical countries of Africa (74.6%), seropositivity in people from malaria endemic areas in Asia and Latin America was far less frequent (28.4% and 44.4%, respectively).

Preparation of purified toxoplasma gondii suspensions.

Simple methods for the preparation of purified suspensions of T. gondii zoites from mouse peritoneal exudate and HeLa tissue cultures are described. The suspensions from the mouse peritoneal exudate were prepared by mechanical disintegration of host cells and tryptic digestion. The average yield of purified Toxoplasma was 78%, with average purity of 99.96%. The suspensions from the tissue cultures were prepared by differential centrifugation and tryptic digestion. The average yield of Toxoplasma was 67% with average purity of 99.67%. An advantage of these procedures is their feasibility.