ELISA absorbance cut-off method affects malaria sporozoite rate determination in wild Afrotropical Anopheles

ABSTRACT. Malaria sporozoite infection rates in a mixed species group of 244 Anopheles gambiae Giles sensu lato and 115 An. funestus Giles wild female mosquitoes were compared using three methods to determine cutoff absorbance values for positivity of a Plasmodium falciparum Welch enzyme-linked immunosorbent assay (ELISA). Positive controls were based on P. falciparum circumsporozoite protein. As negative controls, four wild male Anopheles were included on each microtitre plate; tests were repeated on four consecutive days for each plate.
Infection rates were estimated at 13.1–22.8% using the mean absorbance value of negative controls plus three standard deviations, 11.7–12.8% using double the mean and 12.5–13.6% using the fixed cut-off value of 0.20 (allowing for 20% variation in negative control absorbance values).
Observed agreement for positivity or negativity among samples tested four times was 98.6% for the 2× mean method, 97.2% for the fixed cut-off 0.20 value, but only 82.7% for the mean +3 SD method. It was concluded that the 2× mean cut-off method is most reliable for field studies. P. falciparum sporozoite rates of 12.2% in An. funestus and 11.9% in An. gambiae s. l . were thus determined on the basis of the 2× mean cut-off method.
This comparative evaluation demonstrates that vector infectivity rates can be seriously over-estimated from sporozoite ELISA tests, by as much as 87% in one case considered here, depending on the absorbance cut-off method applied for negative controls.     

A Multi-Unit Sampling System and Its Use in the Characterization of Ultradian and Infradian Growth in Tetrahymena*

SYNOPSIS. A multi-unit automatic sampling device for investigation of microbial growth under a wide variety of conditions is described. The kinetics of asynchronous population growth for batch cultures of Tetrahymena pyriformis (W) at several temperatures show that there are 2 distinct growth phases: an exponential ultradian growth phase that is strongly temperature dependent and a non-stationary growth phase, the infradian phase, that shows little or no temperature dependence over the range from 15–27 C.     

Phylogenetic Position of Amblyospora Hazard & Oldacre (Microspora: Amblyosporidae) Based on Small Subunit rRNA Data and Its Implication for the Evolution of the Microsporidia

ABSTRACT. Sequences of the small subunit rRNA genes of Amblyospora californica and an Amblyospora sp. from Culex salinarius were determined. These sequences were compared phylogenetically with 16 other microsporidia. The results suggest Amblyospora forms a sister taxon to the rest of the microsporidia examined. The basal position of Amblyospora is discussed with respect to the evolution of microsporidian life cycles. These sequences represent the longest microsporidian small subunit rRNA genes sequenced to date, 1,359 and 1,358 bp, respectively. Structural features and GC content (49% for both) are comparable to those of other microsporidia which have been sequenced.     

Control of intracellular glutathione and its effect on ultraviolet radiation-induced K+ efflux in cultured rose cells

Abstract Modification of the ‘intracellular concentration of reduced glutathione’ (IC-GSH) affected the response of cultured rose cells (Rosa damascena) to ultraviolet radiation (UV)-induced leakage of K⁺. High IC-GSH induced by incubation of cells in 10 mol m^?3 GSH (IC-GSH increased linearly with time from 20 to about 600 μmol g^?1 in 61.2 ks) caused cells to become significantly less sensitive to UV. Low IC-GSH induced by treatment with 1 mol m^?3 buthionine sulphoximine (BSO) plus 1 mol m^?3 diethylmaleate (DEM) (IC-GSH decreased from 20 to about 3 μg g^?1 in 61.2 ks) reduced, rather than increased, the UV-sensitivity of the cells. However, treatment with DEM also induced a large transient K⁺ leakage; and treatment with BSO induced a slight leakage. The K⁺ leaked was recovered by 3.24 ks. Following K⁺ recovery, the DEM-treated cells showed almost complete insensitivity to UV, and BSO-treated cells showed a slightly reduced sensitivity to UV. These results are in agreement with our previous findings that other treatments (heat, cycloheximide, UV), which also cause a transient leakage of K⁺, also reduce the induction of K⁺ leakage by a subsequent UV treatment. We conclude that high IC-GSH may play a role in protecting plant cells from UV-induced K⁺ leakage. Increased UV-sensitivity with low ICGSH was not observed, we believe, because of the transient K⁺ leakage, though the mechanism of reduced sensitivity to UV induced by transient leakage of K⁺ is not known at this time. Treatment with UV did not reduce the IC-GSH, showing that this is not the mechanism by which UV induces K⁺ leakage.     

Tropical zooplankton: phenotypic and spatial analyses of polymorphic Ceriodaphnia cornuta (Crustacea: Cladocera)

SUMMARY. 1. The predation-balanced polymorphism of Ceriodaphnia cornuta (a small-eyed horned form and a large-eyed unhorned form) in Lake Gatun, Panama, is re-examined approximately 12 years after the original study (Zaret, 1972a). We consider morphological variability, distribution and fecundity of the population inhabiting Laboratory Bay.
2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.
3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.
4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines.     

Potassium-Ammonium Uptake Interactions in Tobacco Seedlings

Short-term (< 12 h) uptake experiments were conducted with6–7-week-old tobacco (Nicotiana tabacum L. cv. Ky 14)seedlings to determine absorption interactions between K⁺ andNH₄⁺. At equal solution concentrations (0.5 mol m^–3) netK⁺ uptake was inhibited 30–35% by NH₄⁺ and NH₄⁺ uptakewas decreased 9–24%. Removal of NH₄⁺ resulted in completerecovery in K⁺ uptake rate, but NH⁴⁺ uptake rate did not recoverwhen K⁺ was removed. In both cases, inhibition of the uptakerate of one cation saturated as the concentration of the othercation was increased up to 0.5 mol m^–3. The relative effectof K⁺-NH₄⁺ interactions was not altered when Cl- was replacedwith SO₄^2–, but the magnitudes of the uptake rates wereless in the absence of Cl-. The V_max for NH₄⁺ uptake was reducedfrom 128 to 105 µmol g^–1 dry wt. h^–1 in thepresence of 0.5 mol m^–3 K⁺ and the K_m for NH₄⁺ doubledfrom 12 to 27 mmol m^–3 in the presence of K⁺. The resultsof these K⁺-NH₄⁺ experiments are interpreted as mixed-noncompetitiveinteractions. However, an enhanced efflux of K⁺ coupled to NH₄⁺influx via an antiporter cannot be ruled out as contributingto the decrease in net K⁺ uptake. Key words: Nicotiana tabacum, K⁺, NH₄⁺, Uptake interactions