Trypanosoma cruzi: intracellular stages grown in a cell-free medium at 37 C.

A liquid medium containing a high concentration of water-soluble vitamins and ATP was developed for serial cultivation of Trypanosoma cruzi at 27–37 C; fetal bovine serum and trypticase were the only undefined substances in this medium. At 27 C, Trypanosoma cruzi grows primarily (over 99%) as epimastigotes with a population density reaching 92.7 × 10⁶/ml after 12 days of incubation. During the first subculture at 37 C, many epimastigotes from the original inocula changed into metacyclic trypomastigotes after 48 hr; the trypomastigotes subsequently transformed into amastigotes by 96 hr. In the second passage at 48 hr, 57.8% of the organisms were trypomastigotes which changed into amastigotes by the end of the incubation period. The proportion of amastigotes in the third and subsequent passages increased steadily as the proportion of epimastigotes gradually diminished. Amastigotes thus obtained could be serially subcultured indefinitely, yielding population densities of over 3.0 × 10⁷/ml of medium in 4–5 days at 37 C. Available evidence indicates that these amastigotes are morphologically and physiologically similar to intracellular amastigotes.     

Suppression of mouse lymphocyte responses to mitogens in vitro by Trypanosoma cruzi

Maleckar J. R. and Kierszenbaum F. 1984. Suppression of mouse lymphocyte responses to mitogens in vitro by Trypanosoma cruzi. International Journal for Parasitology14: 45–52. The ability of T. cruzi to inhibit mitogen-induced mouse lymphocyte responses was studied to find out if the organism itself is involved in the production of the immunosuppression that occurs during the acute phase of Chagas' disease. Significant suppression of normal spleen cell responses to concanavalin A (a T cell-specific mitogen) or to bacterial lipopolysaccharide (a B cell-specific mitogen) were seen when the concentration of either trypomastigote or epimastigote forms of the parasite reached or exceeded 2.5 × 10⁶ organisms/ml in the cultures. The inhibitory effect was noted over wide ranges of concentrations of either mitogen. Since spleen cells stimulated with mitogenic solutions that had been absorbed with 1 × 10⁷ parasites/ml produced significant responses, the suppressive effect could not be attributed just to mitogen removal by the parasites. Preparations of T. cruzi disrupted by freezing and thawing also inhibited mitogen-induced responses. This indicated that production of suppression was not a result of parasite competition for essential medium nutrients and that trypanosome viability was not required. Suppression was demonstrable only when the parasites were incorporated into the cultures within 12 h after mitogenic stimulation. These results taken together indicate that T. cruzi has the ability to modulate directly or indirectly lymphocyte function by interfering with the initial stages of commitment to lymphoproliferation.     

Leishmania mexicana: Serial cultivation of intracellular stages in a cell-free medium

A cell-free liquid medium has been devised for serial cultivation of Leishmania mexicana pifanoi amastigotes at 33 and 35 C. It consists of tissue culture Medium 199 fortified primarily with a high concentration of water-soluble vitamins, nucleotides, and inactivated fetal bovine serum. The initial pH of the medium is 7.2. Starting with a population of promastigotes as inoculum and serially cultured at 33 or 35 C at 4- to 10-day intervals, the proportion of amastigotes steadily increased and that of promastigotes gradually decreased during the first subculture. By the end of the incubation period in the second subculture, practically all (99%) of the organisms are amastigotes. The amastigotes thus obtained can be cultured indefinitely by serial transfers. In this medium, amastigotes may reach a density of 8 × 10⁷/ml after 10 days of incubation at 33 C, and 5 × 10⁷/ml at 35 C. The medium was modified to have an initial pH of 8.0 by Hepes [4-(2-hydroxyethyl)-1-piperazineethanesulfonic acid] buffer and higher concentrations of sodium bicarbonate. When amastigotes cultured in the original medium at 33 or 35 C are transferred into the modified medium and incubated at 26 C, the amastigotes entirely transformed into promastigotes after three serial passages. These promastigotes could be serially subcultured indefinitely in the modified medium at 4- to 12-day intervals. The promastigotes cultured at 26 C may reach a population density of 7 × 10⁷/ml after 12 days of incubation.     

Cultivation of Trypanosoma theileri at 37 C in Partially Defined Media*

SYNOPSIS. Trypanosoma theileri has become the 1st mammalian trypanosome to be serially cultivated in a blood- and cell-free medium at 37 C. This was accomplished by progressive simplification of an initial culture medium containing whole bovine blood. Fifty-one subcultures in 4- to 5-ml quantities of monophasic liquid media were made over a period of 1 year. The final medium contained hemin and a defined modification of McCoy 5a tissueculture medium, supplemented with a peptone solution. Hemin was essential and T. theileri grew best with ～1 mg/100 ml. Counts reached 8 × 10⁶ organisms/ml in 3–4 days. Seventy-ml volumes of medium supported growth of T. theileri to 3-4 × 10⁶ organisms/ml. Early in the study trypomastigotes were the predominant nondividing form, but they were absent when the medium was being rapidly modified. Trypomastigotes reappeared when the medium was stabilized at the end of the study. Elimination of serum antigens from the medium should greatly facilitate antigenic analysis of T. theileri.     

Cultivation and Morphogenesis of Trypanosoma cruzi in Improved Liquid Media1

SYNOPSIS. Two liquid media (F-29 and F-32) have been developed for the serial cultivation of T. cruzi amastigotes. F-29 consists of synthetic tissue culture fluid 199, trypticase, hemin and bovine fetal serum; F-32 is F-29 plus chicken plasma. The inocula for serial cultivation in both media contained over 99% epimastigotes. The proportion of structural types in the original inocula did not change significantly during 10 serial passages in F-29 medium at 29.5 C. However, in the 2nd passage in F-29 medium at 35.5 C most of the organisms becme amastigotes, and after several more subcultures over 92% were amastigotes. During the original passage in F-32 medium at 35.5 C. over 90% of the organisms were trypomastigotes with terminal kinetoplasts. After several more passages, and regardless of incubation temperature (29.5–35.5C), over 94% became amastigotes. In either F-29 or F-32 a 7-fold increase of amastigotes may be obtained after 4-day incubation at 35.5 C.     

Trypanosoma cruzi: defined medium for continuous cultivation of virulent parasites.

A liquid medium was developed for the continuous cultivation of Trypanosoma cruzi. Among the several highly purified macromolecules tested only bovine liver catalase, horseradish peroxidase, lactoperoxidase, and bovine hemoglobin supported the continuous growth, at high yield, of mice-virulent Trypanosoma cruzi; other hemoproteins were inactive. Bovine liver catalase showed optimal Trypanosoma cruzi growth-promoting activity, parasites reaching 20 × 10⁶ parasites/ml (95% epimastigotes) at about 10 days in most of the 45 subpassages to date. Furthermore, this protein in the incubation medium provided all the amino acid requirements of actively growing parasites, thus eliminating the need for exogeneous free amino acids. Additional experiments revealed that the hemoprotein's growth-promoting activity was independent of any enzymatic activity and that reconstituting the exact protein composition by means of exogeneous amino acids did not support parasite multiplication, suggesting the importance of the primary structure of the active proteins for growth-promoting activity. These active macromolecules supported the multiplication of five different strains of Trypanosoma cruzi, but did not support Leishmania brasiliensis or Leishmania mexicana proliferation, suggesting species specificity.     

Immunization of mice with irradiated Trypanosoma cruzi grown in cell culture: Relation of numbers of parasites,immunizing injections,and route of immunization to resistance

Mice were given 5 or 8 weekly injectins of either 2·0 × 10⁶ or 20·0 × 10⁶ irradiated T. cruzi from cell culture (ratio of trypomastigotes to amastigotes, 1 : 1) via the intraperitoneal route or via the subcutaneous route and challenged via the subcutaneous route one week after the last injection with 5·0 × 10⁴T. cruzi in mouse blood. The irradiated parasites used were not capable of producing infections in either Vero cell cultures or C₃H mice. Mice receiving irradiated parasites were significantly protected against the challenge infection as evidenced by significantly lower mean parasitemia, lessened signs of acute disease, and reduced mortality than that observed in untreated controls. Mice receiving 5 weekly immunizing injections of irradiated parasites were more resistant to challenge than those receiving 3 in previous work. Mice receiving 8 weekly immunizing injections were not significantly more protected against challenge than those receiving 5. Mice given 5 weekly injections of 20·0 × 10⁶ irradiated parasites were significantly more resistant to challenge than those receiving 2·0 × 10⁶ irradiated parasites on the same schedule. Mice given 5 weekly intraperitoneal injections of 20·0 × 10⁶ irradiated parasites were significantly more resistant to challenge than those receiving an equivalent number of immunizing injections via the subcutaneous route.     

Induction of apogamy inEquisetum arvense

InEquisetum arvense, apogamous sporophytes were produced on medium containing 5×10^?6–5×10^?8 g/ml kinetin. NAA, IAA, GA₃, glucose and saccharose were ineffective for the induction of apogamy. On medium containing 5×10^?7–5×10^?8 g/ml kinetin, the gametophytes passed into sporophytic structures directly. On medium containing 5×10^?6 g/ml kinetin, some gametophytes passed into sporophytic structures directly, and others became a callus-like cell mass from which an apogamoun shoot arose. The results of the morphological observations on them were reported and compared with the sexually produced sporophyes. The apogamous sporophytes induced by 5×10^?7 g/ml kinetin were haploid in their nuclear phase and some of those induced by 5×10^?6 g/ml kinetin had a tendency to become diploid.     

Trypanosoma cruzi: effects of anti-thymocyte serum in mice and neonatal thymectomy in rats

CF₁ mice were given eight injections of normal rabbit serum (NRS), Hanks' balanced salt solution (HBSS), or rabbit anti-mouse thymocyte serum (ATS) beginning 3 days prior to and at 3-day intervals subsequent to intraperitoneal (ip) inoculation with 5 × 10⁴ trypomastigotes of a Brazil strain of Trypanosoma cruzi. Markedly enhanced parasitemia, increased numbers of tissue stages (amastigotes), and higher mortality occurred in ATS-treated mice as compared to NRS- or HBSS-treated controls. Administration of three injections of ATS at 3-day intervals during the latter stages of acute Chagas' disease, i.e., when numbers of parasites were declining, resulted in a transitory relapse (increase in numbers) of blood and tissue parasites. No relapse occurred in mice when ATS was administered at 3-day intervals over a period of 15 days during the subacute stage of the disease, i.e., after parasites had disappeared from the blood.Parasitemia and mortality were enhanced in neonatally thymectomized rats when compared to that observed in sham-operated and unoperated control rats following ip injection of 2 × 10⁵ trypomastigotes of T. cruzi. Serum obtained from thymectomized and control rats 5 weeks after inoculation with T. cruzi at a time when the blood of all animals had become microscopically negative for parasites were equally protective in passive transfer experiments, while serum from uninfected controls gave no protection.Gamma globulin levels significantly increased in thymectomized as well as intact rats by the third to fourth week of infection with T. cruzi, reached maximum concentrations in 5–6 wk, and remained elevated significantly at the twelfth week post infection as compared with uninfected controls. No significant changes occurred in total serum proteins or α and β fractions of any group, infected or uninfected.Total circulating leukocytes, especially lymphocytes, were diminished in mice and rats subjected to treatment with ATS or neonatal thymectomy.These data clearly indicate that neonatal thymectomy of rats and ATS treatment of mice suppress the acquired immune response to T. cruzi. Further, passive transfer experiments in rats confirm the protective role of circulating antibody in acquired immunity to Chagas' disease.     

Growth and Immunologic Studies on the Culture Forms of Trypanosoma lewisi*

SYNOPSIS. Culture forms of Trypanosoma lewisi grown at 27 C in a diphasic blood agar medium resemble in structure the stage found in the invertebrate host. Cultures inoculated with approximately 1 × 10⁶ trypanosomes/ml attain maximum populations of 2–7 × 10⁷ organisms/ml after 5–6 days of incubation. The stationary phase persists 6–15 days. The decline of the population is of relatively long duration with approximately 1 × 10⁶ viable organisms/ml present after 90 days. Variations in growth were attributed to the preparation of defibrinated heated rabbit blood incorporated into the culture medium. With inocula of 3.0 × 10⁵ trypanosomes/ml there was a lag in growth not observed with larger inocula. Trypanosomes incubated at elevated temperatures had altered growth curves compared to organisms at 27 C. Agitation of cultures did not affect the growth or stationary phases, but hastened the population decline. Heated and unheated 5% (v/v) normal rat serum incorporated in the liquid phase of the medium altered the growth of the organisms. Heated serum caused a decrease in the population and an extended lag phase. The effects on growth were more marked with unheated serum suggesting that both heat-stable and labile components affect growth. Antisera from rats injected with live culture forms included in the liquid phase inhibited, while antisera from rats 24 days after infection with the blood stream forms had no effect on the growth of the culture forms. Antisera from rabbits immunized with sonicates of culture forms also altered the growth of the organisms in culture. Rabbit antisera prepared by immunization with sonicates of dividing and non-dividing blood stream forms had no effect on the in vitro growth. Antisera from animals immunized with rat blood and culture medium were also without effect. The immunologic implications of the data are considered and discussed.     

The serum growth and survival requirements of SV40-transformed 3T3 cells

Summary Simian virus 40-transformed 3T3 cells are dependent on serum for survival and growth. This growth activity can be separated on a pH 2 Sephadex G100 column into two fractions: a high molecular weight activity and a low molecular weight substance that has recently been characterized as containing as its major agent, biotin. To replace the remainder of the serum requirement, hormones and other growth factors were tested. Both insulin at high, nonphysiological concentrations (200 to 500 ng/ml) and transferrin (5×10⁻⁸ M) stimulate the growth rate in low serum medium (0.3% v/v bovine calf serum DME) individually and, when added together, are nearly as growth enhancing as 10% serum. The need for the residual serum in this medium can be eliminated by the use of crystalline trypsin during trypsinization. Under these serum-free conditions, biotin and transferrin supplementation provide for moderately good growth (20 to 30 hr population doubling time, 1×10⁶ cells/3.2-cm dish final cell density). Insulin addition further stimulates the growth rate (16 to 20 hr) and the final density (1.5×10⁶ cells). Although the protein growth factors, EGF (0.5 to 1.0 ng/ml) and FGF (4 to 10 ng/ml), also appear to enhance growth individually and additively, their effects are slight and very variable. Nevertheless, the complete serum-free medium (DME supplemented with biotin, transferrin, insulin, EGF and FGF) yields growth comparable but still inferior to 10% serum supplementation (14-versus 12-hr population doubling time, 1 to 2×10⁶ versus 2 to 3×10⁶ cells final cell density). This work was supported by NIH Grant CA 20040.     

Use of cadmium hydroxide gel for isolation of extracellular catalases from Penicillium piceum and characterization of purified enzymes

We optimized the conditions for isolation of extracellular catalases from Penicillium piceum F-648 and P. piceum A3 by means of volume chromatography with cadmium hydroxide gel. Our study showed that 55–57 mg wet gel are sufficient for the maximum sorption of catalase from 1 ml of culture fluid. This gel was formed in 1 ml 70 mM Cd(NO₃)₂ after addition of NaOH (Cd(NO₃)₂/NaOH molar ratio 1: 2.2). The eluting solution contained 50 mM NaH₂PO₄(pH 7.0), 5.0 mM dithiothreitol, and 0.3% sodium cholate and was potent in desorbing catalase from the gel. Subsequent ultrafiltration of the eluate on the membrane with a retention limit of 50 kDa allowed us to concentrate and purify the sample from low-molecular-weight protein impurities. NH₄Cl (1.0 M) containing 0.3% sodium cholate was used to wash the sample from low-molecular-weight aromatic metabolites. Purified catalases included 33–34% antiparallel β-structures and 9%-spirals. Under optimal conditions in the medium of 10 mM phosphate buffered saline (pH 7.0) at 30°C, catalases from P. piceum F-648 were characterized by the following parameters: K _M, 158.8 mM; catalytic constant, 2.83 × 10⁶ s^?1; enzyme inactivation rate constant in H₂O₂ decomposition, 3.5 × 10^?2 s^?1; and constant of the interaction between catalase complex I and second molecule of H₂O₂, 1.8 × 10⁷M^?1 s^?1.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.     

New Culture Medium for Maintenance of Tsetse Tissues and Growth of Trypanosomatids*

SYNOPSIS. A new culture medium (SM), based on the amino-acid composition of tsetse hemolymph and containing fetal bovine serum, was designed for the maintenance of tsetse organs and the cultivation of various trypanosomatids. For optimum growth 20% (v/v) serum was required. The medium supported prolonged peristalsis of the alimentary tract and salivary glands of pre-emerged Glossina morsitans morsitans. In established cultures, derived from bloodstream forms of pleomorphic Trypanosoma brucei brucei and Trypanosoma brucei rhodesiense strains, inocula of ～ 10⁶ procyclics/ml yielded 4–5 × 10⁷ organisms/ml after 4 or 5 days of incubation at 28 C. Bloodstream forms of a cloned monomorphic T. b. brucei strain were also able to transform into procyclics, which, however, multiplied at a lower rate, with maximum yields of ～ 2 × 10⁷ after 5 days. Cultures of Trypanosoma congolense and of a nearly monomorphic Trypanosoma brucei gambiense strains could be established in SM medium only in the presence of tsetse alimentary tract. The procyclic trypomastigotes of these species, adapted to SM medium and able to grow in it without Glossina organs, gave maximum populations of ～ 4.5 × 10⁷ cells/ml. Promastigotes of Leishmania donovani, cultivated routinely in a diphasic Table's medium, multiplied actively upon being transferred into SM medium, producing yields of ～ 4 × 10⁷ cells/ml.     

Tolerance induction to a thymus-dependent antigen in vitro: treatment of nonadherent cells with tolerogen biologically filtered in vitro

Highly tolerogenic bovine gamma globulin (BGG), a thymus-dependent antigen, was prepared by biologic filtraration in vitro. It readily induced tolerance in vivo in BALB/c mice and also rendered their nonadherent lymph node cells tolerant after in vitro incubation. Biologic filtration in vitro was carried out by incubating 2.5 × 10⁷ lymph node cells with 10 mg of nontolerogenic BGG in 10 ml of Eagle's medium containing 2% normal mouse serum at 37 °C for 6 hr. The BGG-containing medium was clarified by centrifugation and was used without further dilution.For tolerance induction in vitro, lymph node cells were separated into adherent and nonadherent populations on Falcon plastic. These cells were incubated for 0–18 hr at 37 °C with biologically filtered BGG (bBGG). After incubation, the cells were washed three times and (2–2.5) × 10⁷ nonadherent or 4 × 10⁶ adherent cells were injected iv with their untreated counterpart into lethally irradiated mice which had received 10⁶ bone marrow cells. The recipients were then challenged with 300 μg of aggregated BGG, and tolerance was assayed by the elimination of labeled BGG, rosette formation, and passive hemagglutination. Spleen cells were similarly treated for comparison. Our findings show that tolerance was not induced in vitro in adherent lymph node cells. However, in the nonadherent populations, those from the lymph node but not the spleen were rendered tolerant. The acquisition of tolerance in vitro was gradual. It was dependent upon the length of exposure to bBGG and required at least 6 hr.     

Serological and vaccination studies with bloodstream and culture forms of Trypanosoma musculi

Khazindar S. H. and Dusanic D. G. 1982. Serological and vaccination studies with blood-stream and culture forms for Trypanosoma musculi. International Journal for Parasitology12: 257–264. Trypanosoma musculi bloodstream forms (BSF) were collected from immunosuppressed infected mice and extracted with phosphate buffered saline (PBS). ML-15, O'Daly's and LMC media, each containing 5% fetal calf serum (FCS) and a dialysate medium were investigated to identify the medium providing the optimal growth of T. musculi culture forms (CF). Because of the ease of preparation, ML-15 containing 5% FCS was selected and the culture forms were harvested when the parasites attained concentrations of at least 1 × 10⁷ trypanosomes/ml. Cellular antigens present in PBS extracts of the BSF and CF parasites were analyzed with rabbit antisera by crossed immunoelectrophoresis and tandem crossed immuno-electrophoresis. Absorptions of rabbit antisera with CF, BSF, media and normal mouse blood extracts were performed on immunoabsorbent affinity columns prior to crossed immunoelectrophoresis to further study the unique and shared antigens of the parasites. A minimum of 13 antigens were shared by these trypanosomes. Four antigens appeared to be unique to BSF and a single antigen to CF. In immunization studies, two groups of C3H/Anf mice were immunized with the equivalent of 1 × 10⁸ frozen-thawed BSF or CF/injection. Two groups of five animals injected with PBS or uninoculated medium and one untreated group served as controls. Animals in each group received 6 injections administered at 3-day intervals. Three days following the last injection, all animals were challenged with 1 × 10⁴ BSF. Hemacytometer counts were performed every 4 days until no parasites were seen in wet blood preparations of the untreated group. None of the animals inoculated with BSF homogenate displayed parasitemias, while animals inoculated with CF homogenate were found to be infected. Parasitemias in mice immunized with CF were lower than those of the control mice.     

Developement of serum-free media in CHO-DG44 cells using a central composite statistical design

A serum free medium was developed for the production of recombinant antibody against Botulinum A (BoNTA) using dihydrofolate reductase deficient Chinese Hamster Ovary Cells (CHO-DG44) in suspension culture. An initial control basal medium was prepared, which was similar in composition to HAM’s F12: IMDM (1:1) supplemented with insulin, transeferrin, selenium and a lipid mixture. The vitamin concentration of the basal medium was twice that of HAM’s F12: IMDM (1:1). CHO-DG44 cells expressing S25 antibody grew from 2 × 10⁵ cells to maximum cell density of 1.04 × 10⁶ cells/ml after 5 days in this control medium. A central composite design was used to identify optimal levels and interaction among five groups of medium components. These five groups were glutamine, Essential Amino Acids (EAA), Non Essential Amino Acids (NEAA), Insulin, Transferrin, Selenium (ITS), and lipids. Fifty experiments were carried out in four batches, with two controls in each batch. There was little effect of ITS and Lipid concentrations over the range studied, and glutamine concentration showed a strong interaction with EAA. The optimal concentrations of the variables studied were 2.5 mM Glutamine, 7.4 mM (2×) EAA, 1.4 mM (0.5×) NEAA, 1× ITS supplement, 0.7× Lipids supplement. The maximum viable cell density attained in the optimized medium was 1.4 × 10⁶ cells/ml, a 35% improvement over the control culture, while the final antibody titer attained was 22 ± 3.4 μg/mL, a 50% improvement.     

Agglutination of Trypanosoma cruzi by Concanavalin A*

Epimastigotes of Trypanosoma cruzi obtained in culture agglutinate readily with low concentrations of concanavalin A (Con A). Agglutination was linear with time up to 10 min providing that the initial cell density was greater than 1 × 10⁸ cells/ml. Under these conditions, the percentage agglutination was dependent on the Con A concentration. Agglutination was inhibited by α-methyl D-mannoside, α-D-mannose, and α-D-glucose. Pretreatment of cells with trypsin had no effect on the epimastigote agglutinations. Blood forms (trypomastigotes) of T. cruzi did not agglutinate even in the presence of 100 times more Con A. Results suggest differences in membrane structure between blood forms and cultured epimastigotes of T. cruzi. These membrane differences might be related to the different pathogenic properties of both cell forms of T. cruzi.     

Levels of aflatoxin B1, bacteria and fungi in feed and food in 1971 — 1987

Totally 39% out of 8371 feed and their component samples were contaminated by aflatoxin B₁. Mean contamination was 36μg/kg with maximum yield 10100 μg/kg. Contamination of samples by total count of organisms, mean contamination and maximum yield, respectively was: 1) bacteria 99%, 2.2×10⁶, 2.4×10⁸; 2) proteolytic bacteria 94%, 1.2×10⁵, 3.0×10⁶;3) moulds 98%, 1.3×10⁵, 9.0×10⁶; 4) yeasts 44 %, 3.3×10⁴, 3.6×10⁶. The samples were contaminated in 92 % byAspergillus spp, in 71% byAspergillus flavus, in 83% byPenicillium spp, and in 20% byFusarium spp with mean contamination 8.3×104, 1.1×10³, 4.2×10⁴, 5.0×10³ , and maximum yield 6.8×10⁶, 1.0×10⁵, 5.0×10⁶, 1.5×10⁶, respectively. Totally 8.5% of strains were aflatoxinogenic and 4.4% of the strains were isolated from feed and 21 % of the strains from grain/nut.     

An improved heat-stable glutamine-free chemically defined medium for growth of mammalian cells

A heat-stable chemically defined medium, free of glutamine, is described for the growth of mammalian cells in suspension culture. The presence of L-alanine in the defined medium permitted the omission of glutamine. A 22-fold increase in the population of a substrain of mouse L cells was obtained (3.4 × 10⁶ cells/ml) in six days with no medium replenishment during incubation. Maximum yields (27 × 10⁶ cells/ml) were obtained by daily medium replacement and venting of cultures. Growth was also improved in a line of cat kidney cells and HeLa cells, and in another substrain of L cells.