Two new viruses, goldfish virus-1 (GFV-1) and goldfish virus-2 (GFV-2), were isolated from swimbladder cultures prepared from healthy Carassius auratus (L.). The isolates were sensitive to pH, heat, and chloroform but stable to freezing and thawing. Treatment with IUDR, Feulgen staining and acridine orange staining indicated that the viruses contain double-stranded DNA. Electron microscopy revealed enveloped virions of 180 nm enclosing icosahedral capsids of 120 nm. Viral growth was studied by light and electron microscopy and infectivity assays. Virions were assembled in cytoplasmic inclusion bodies and apparently released through cell degeneration. Infectious virus was first produced at 24 h post-infection. Progressive cytopathology was observed leading to cell ghosts by 96 h post-infection. The results suggest tentative placement of the viruses in the family Iridoviridae.
The cytotoxic effect of staphylococcal enterotoxin B upon human embryonic intestine cell cultures is characterized by retraction of cells from the monolayer. This is followed by clumping of the retracted cells to form clear areas in the monolayer and finally by sloughing of the clumps from the glass surface. The 50% effective dose of the toxin, determined by protein analysis of the cultures used in titration studies, was found to be between 40 and 60 pg/ml. The cytotoxic property of the enterotoxin was completely neutralized by 3.9 x 10-6 ml of specific antitoxin per ,ug of toxin. The cytotoxicity was found to be slightly enhanced by 2.2 g of bicarbonate per liter of Eagle's basal medium (Earle's salt solution level), the absence of serum, the absence of penicillin and streptomycin, and the presence of 2.8 mmoles of calcium in the medium. The cytotoxicity was profoundly influenced by the age of the culture. No cytotoxicity was evident until after 2 days of growth had taken place, when the cell number was approximately 4.0 X 105 cells per culture.
Studies on the biological action of diphtheria toxin on tissue and cell cultures have been reviewed by Solotorovsky and Gabliks (1) and by Pappenheimer, Jr., et al. (2). Numerous investigations on differences in cell susceptibility have shown that cell cultures derived from diphtheria toxin-sensitive animals (guinea pig, rabbit, dog, monkey, and man) and those derived from resistant animals (rat and mouse) reflect the characteristic susceptibility or resistance of the donor animal. The previous report by Gabliks and Solotorovsky 0 ) shows that the cultures derived from diphtheria toxin-resistant animals, the rat and mouse, tolerate about 100,000 times more toxin than the cultures derived from sensitive animals, such as the guinea pig, rabbit, and man. Explanation for these significant differences in cell susceptibility to diphtheria toxin is unknown; certain possibilities are explored in the present study which describes some of the initial effects of toxin on susceptible cells and indicates an alteration of the toxin during exposure to susceptible cell culture. Metkods and MaterialsCd/ C~dt~re~.--Three human cell lines were used as diphtheria toxin-susceptible cells: Chang liver, derived from normal liver tissue; HeLa, derived from cervical carcinoma; and KB, derived from laryngeal cardnoma. The human cultures were grown in Eagle's basal medium (4) supplemented with 10% calf serum. The toxin-resistant mouse lines, liver NCTC 1469, derived from normal liver, and L-929, derived from subcutaneous tissue, were grown in medium 199 (5) supplemented with I0 to 20% horse serum. All listed stock cultures were obtained from Microbiological Associates, Inc., Bethesda, Maryland.For experimental work, cells were suspended in the appropriate growth medium containing 100 units per ml penicillin and 100 pg per ml streptomycin. 1 ml volumes of cell suspensions at a concentration of 7 X 104 cells per ml were planted in screw-capped culture tubes. The cultures were incubated in a stationary position at 37°C for 2 days to develop cell monolayers.DiphlJ~ia Toxin and Ant//o:6n.--Most experiments were conducted with a crude diphtheria toxin preparation to assess the effects of all components which might be associated with *
Aflatoxin B1, a metabolite of the mold Aspergillus flavus, is toxic to cell cultures. The toxic effect is evidenced by an inhibition of growth followed by progressive granulation, rounding, and finally sloughing of the cells from the glass. In studies with embryonated eggs, duck embryos were found to be four to five times more susceptible than chick embryos. In studies on Chang liver cultures, there were decreases in cell number, protein, ribonucleic acid (RNA), and deoxyribonucleic acid (DNA) per culture with increasing aflatoxin B1 concentrations. Since the cell number decreased and the protein, RNA, and DNA content per cell increased with increasing concentrations of aflatoxin, enlarged cells were suggested. These data are consistent with in vivo data of other workers who have found hypertrophic cells with enlarged nuclei in histological studies on the tissues of rats and ducklings fed toxic peanut meal.
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