In vivo 1H MRS can be used to detect and quantify the lactate resonance at 1.3 ppm provided that overlapping lipid resonances are eliminated. A homonuclear spectral editing method was developed to acquire uncontaminated 1H spectra of lactate with adiabatic pulses. An advantage of the adiabatic pulse sequence is the ability to induce uniform flip angles and to maximize sensitivity in applications employing surface coil transmitters which produce highly inhomogeneous B1. Glycolytic activity in an intracerebral C6 glioma in rats was monitored by using adiabatic editing sequences to observe [3-13C]lactate produced from infused [1-13C]glucose. Acute hyperglycemia (serum glucose > 22 mM, n = 10) had no significant effect (P = 0.08) on the total ([12C] + [13C]) tumor lactate signal intensity.

The viability of Giardia muris cysts was studied with the fluorogenic dyes fluorescein diacetate (FDA) and propidium iodide (PI). G. muris cysts were seen to fluoresce intensely green with FDA at an excitation wavelength of 450 to 490 nm. Cysts stained with PI fluoresced bright orange at an excitation wavelength of 450 to 490 nm and bright red at 545 to 546 nm. Examination of isolated G. muris cyst preparations stained with FDA-PI revealed that greater than 85% of the cysts stained green with FDA and less than 15% stained orange-red with PI. Using the mouse model for giardiasis, we inoculated FDAor PI-stained cysts into neonatal mice. Feces were examined at days 3, 5, 8, and 11 postinoculation for the presence of cysts. Using 1,000 FDA-stained cysts as the inoculum, we detected cysts at days 5, 8, and 11 postinoculation in 19 of 19 mice, whereas a 50-fold greater dose of cysts produced infection in 27 of 27 mice at day 3 as well as at days 5, 8, and 11 postinoculation. Inoculation of mice with either 5,000 or 50,000 PI-stained G. muris cysts did not produce infection in any of the animals. Necropsy of mice infected with FDA-stained cysts showed trophozoites within the intestines. No trophozoites were detected within animals inoculated with PI-stained cysts. These results demonstrate that FDA-positive cysts are viable, as determined by infectivity, while PI-positive cysts are nonviable and incapable of producing G. muris infections in vivo. The development of this rapid and inexpensive test should facilitate testing of the effects of various chemical agents and environmental factors on the viability of Giardia cysts.

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Numerous waterborne outbreaks of giardiasis have occurred since 1965, yet little or no information has been reported on the viability of Giardia cysts in different aquatic environments. We have studied the viability of Giardia muris cysts suspended in lake, river, and tap water, while also monitoring water temperature, dissolved oxygen, pH, and other water quality parameters. Fecal pellets containing G. muris cysts were placed in glass vials covered with filter paper and exposed to (i) lake water at 15 ft (ca. 4.6 m) and 30 ft (ca. 9.2 m), (ii) river water, (iii) tap water, and (iv) distilled water stored under laboratory conditions. At 3, 7, 14, 28, 56, and 84 days, two vials from each environment were removed, and cyst viability was determined by (i) fluorogenic dye exclusion, (ii) production of giardiasis in an animal, and (iii) cyst morphology by Nomarski microscopy. In the fall, the cysts suspended at 30 ft in lake water remained viable for up to 56 days whereas cysts stored at 15 ft were nonviable after day 28. The G. muris cysts exposed to river water remained viable up to 28 days as determined by the production of giardiasis in mice. G. muris cysts suspended in tap water showed no signs of viability after 14 days, while cysts serving as controls (exposed to refrigerated distilled water) remained viable for up to 56 days. In the winter, Giardia cysts suspended in either lake or river water were viable for 56 to 84 days whereas cysts exposed to tap water were nonviable by day 14. Comparison of water quality parameters with the results of viability determination revealed that only decreased water temperature (<100C) was consistent with prolonged survival of G. muris in different types of environmental water.

Examination of Giardia muris cysts stained with the fluorogenic dyes, fluorescein diacetate (FDA) or propidium iodide (PI), by either Nomarski differential interference contrast (DIC), phase, or brightfield (BF) microscopy revealed a direct correlation between morphologic appearance and uptake of FDA or PI. Cysts incorporating FDA were all morphologically identical and exhibited (1) a clearly delineated cyst wall, (2) the presence of a distinct space between cyst wall and cytoplasm, and (3) flagella recognizable at one pole of the cyst. FDA-positive cysts also had a hyaline appearance of the cytoplasm (examined at multiple focal planes with DIC) that made it very difficult to detect the presence of nuclei, intracellular axonemes of flagella, or curved elements of the adhesive disc. However, PI-stained cysts possessed a distinct morphology that was clearly different from that of FDA-stained cysts. Examination of PI-stained cysts demonstrated the presence of well-defined nuclei, intracellular axonemes, and curved elements of the adhesive disc. The cytoplasm of PI-stained cysts contained a fine granular texture as opposed to the hyaline appearance of FDA-stained cysts, and no space was observed separating the cyst wall from the underlying cytoplasm in the PI cyst. This light microscopic comparison of viable FDA- and nonviable PI-stained cysts of G. muris demonstrates that 2 types of cysts can be distinguished and implies that structural differences can be used to identify these subpopulations of cysts.(ABSTRACT TRUNCATED AT 250 WORDS)