Carcinogenicity of biphenyl in mice by two years feeding

Carcinogenicity and chronic toxicity of biphenyl was examined in the male and female BDF1 mice fed a diet containing biphenyl at 667, 2,000 or 6,000 ppm for 2 years. There was no difference in survival rate between any biphenyl-containing diet-fed group of either sex and the respective control. Body weights of the males and females fed 6,000 ppm diet were significantly lower than the respective control. Incidences of hepatocellular carcinomas and hepatocellular adenomas in the females fed diets containing biphenyl were significantly increased in a dose-related manner, and exceeded a range of the historical control data in the Japan Bioassay Research Center. Incidences of basophilic cell foci in the liver were increased in the females fed 2,000 and 6,000 ppm diets. There was no increase in tumor or tumor-related lesion in the males fed diets containing biphenyl. Chronic toxicity of biphenyl was characterized by increased incidences of urothelial desquamation in the renal pelvis in males and females and mineralization in the inner stripe of renal outer medulla in females, as well as changes in serum levels of BUN, ALP and some electrolytes in males and females. In conclusion, the 2-year oral administration of biphenyl-containing diets induced pre-neoplastic and neoplastic lesions in the liver of females and non-neoplastic lesions in the kidney of males and females. Causative factors for the biphenyl-induced hepatocarcinogenicity were discussed in light of our published finding of peroxisome proliferation.     

Tumor promoting effect of phenolphthalein on development of lung tumors induced by N-ethyl-N-nitrosourea in transgenic mice carrying human prototype c-Ha-ras gene

In order to examine tumor modifying effects of phenolphthalein (PhP), female transgenic mice carrying human prototype c-Ha-ras gene (rasH2 mice) were given a single intraperitoneal injection of 60 mg/kg body weight of N-ethyl-N-nitrosourea (ENU), followed by the diet containing 12,000 ppm PhP for 26-week. Histopathologically, alveolar hyperplasias, adenomas and adenocarcinomas were observed in the ENU + PhP group, but only hyperplasias and adenomas were observed in the ENU alone group. The incidence and multiplicity of adenocarcinomas in the ENU + PhP group was significantly increased as compared to that in the ENU alone group. The combined multiplicity of adenomas and adenocarcinomas in this group was also significantly higher than that of the ENU alone group. In addition, the ratio of area of adenomas in the ENU + PhP group was significantly higher than that in the ENU alone group. The result of our study suggests that PhP has a clear tumor promoting effect in the lung of rasH2 mice.     

No Modifying Effect of Antioxidant N-Acetyl-L-Cysteine on Fenofibrate-induced Hepatocarcinogenesis in Rats

To clarify the modifying effect of N-Acetyl-L-Cysteine (NAC), which has antioxidative ability, on hepatocarcinogenesis promoted by fenofibrate (FF), a peroxisome proliferator-activated receptor (PPAR) alpha agonist , male F344/N rats were administered a single intraperitoneal injection of N-diethylnitrosamine (DEN) as an initiator followed by administration of a diet containing 3,000 ppm of FF for 16 weeks. Two-thirds partial hepatectomy was performed 1 week after the FF treatment. Additionally, NAC treatments for 14 weeks from 2 weeks after the FF treatment were performed. Although the expression level of tumor protein p53 (Tp53) mRNA decreased in the DEN+FF+NAC group as compared with that in the DEN+FF group, no significant differences between the DEN+FF and DEN+FF+NAC groups were observed in the number of hepatocellular altered foci and activities of hepatocellular proliferation. In addition, the results of an antioxidant enzyme assay and measurement of the amounts of total glutathione in the liver revealed no significant difference between the DEN+FF and DEN+FF+NAC groups; although no significant differences were observed in many genes between the DEN+FF and DEN+FF+NAC groups, only glutathione peroxidase 2 (Gpx2) mRNA increased in the DEN+FF+NAC group as compared with the DEN+FF group. The results under the present experimental conditions indicate no obvious modifying effect of NAC on liver tumor promotion by FF in rats.     

Dimethylnitrosamine-induced liver fibrosis and recovery in NOD/SCID mice

There is a need for a new liver fibrosis model of immunodeficient mice to study the effects of cell therapy on liver disease because there are not many animal models available to study the effects of cell therapy. In this study, we induced liver fibrosis using dimethylnitrosamine (DMN) in NOD/SCID mice to create an animal model for liver disease. DMN (5 mg/kg, i.p.) was injected intraperitoneally for three consecutive days per week for 6 or 8 weeks, and the mice were sacrificed at weeks 0, 4 and 8 after the last DMN injection. The 6-week DMN-treated group gradually recovered from serum biochemical changes, histopathological toxic effects and lesions in the liver at weeks 4 and 8 after the last DMN injection. However, the progression of liver fibrosis and toxic levels were maintained in the 8-week DMN-treated group at week 4 after the last DMN injection. The increases in iron and extracellular matrix (collagen) in the DMN-treated group were confirmed by Prussian blue (PB) and Masson's trichrome (MT) staining, respectively. Additionally, activation of hepatic stellate cells was observed by alpha smooth muscle actin (α-SMA) immunostaining and western blot. In conclusion, treatment of NOD/SCID mice with 5 mg/kg of DMN for 8 weeks can be used to induce an appropriate animal model of disease for liver fibrosis. This model may be useful for evaluation of the efficacy and safety of cell therapies such as human mesenchymal stem cell therapy.     

Effects on the Local Immunity in the Testis by Exposure to Di-(2-ethylhexyl) Phthalate (DEHP) in Mice

Exposure to di-(2-ethylhexyl) phthalate (DEHP) has been reported to induce spermatogenic disturbance through oxidant stress and affect the immune system as an adjuvant. However, the effect of DEHP on the testicular immune microenvironment has not yet been investigated. In the present study, we examined the testicular immune microenvironment after exposure to doses of DEHP, previously identified as no-observed-adverse-effect levels. Adult male mice were administered food containing 0%, 0.01% or 0.1% DEHP and then testes were analyzed. The results showed that a slight but significant spermatogenic disturbance appeared in the 0.1% DEHP group but not in the 0.01% DEHP group at 8 weeks. It was also demonstrated that lymphocytes and F4/80- and MHC class II- positive cells were significantly increased with the elevation of IL-10 and IFN-γ mRNA expressions in the testes of not only the 0.1% DEHP group but also the 0.01% DEHP group at 8 weeks. Histochemical analyses involving horseradish peroxidase (HRP) as a tracer showed that a little blood-borne HRP had infiltrated into the lumen of a few seminiferous tubules beyond the blood-testis-barrier in both the 0.1% and 0.01% DEHP groups at 8 weeks. This indicates that a dose of DEHP that has little effects on spermatogenesis can change the testicular immune microenvironment with functional damage of the blood-testis barrier.     

Sequential observation of 2,6-dimethylaniline-induced nasal lesions in a rat two-stage nasal carcinogenesis model after initiation with N-bis(2-hydroxypropyl) nitrosamine

Male F344 rats received diet containing 3,000 ppm 2,6-dimethylaniline (DMA) after initiation with a single subcutaneous injection of 2,400 mg/kg of N-bis(2-hydroxypropyl)nitrosamine (DHPN), and histological and electron microscopic examinations of the nasal cavity were performed at 4, 13, 26 and 52 weeks to examine sequential changes induced by DMA. Severe atrophy of Bowman's glands and epithelial disarrangement were apparent from week 4, followed by dilatation and/or proliferation of Bowman's glands, degeneration of epithelial cells, and proliferation of undifferentiated epithelial cells from week 13. Focal glandular hyperplasias, dysplastic foci, and adenomas were observed from week 26, and carcinomas at 52 week. These nasal lesions were mostly evident in the olfactory mucosa in the nasal cavity, and their severity and/or incidences, other than atrophy of Bowman's glands, increased with the treatment period. Electron microscopically, carcinoma cells demonstrated desmosomes, dense secretory granules identical to those in normal Bowman's glands, a basement membrane, and microvilli. These results suggest that Bowman's glands are the target of DMA, giving rise to nasal carcinomas after DHPN-initiation.     

The Pathology of Vinyl Chloride Exposed Mice

Outbred albino laboratory mice were exposed to 50 p.p.m. and 500 p.p.m. vinyl chloride by inhalation 6 hrs./day, 5 days/week during 52 and 26 weeks, respectively. Pathologic examination showed the presence of histologically benign alveologenic lung adenomas, haem-angiosarcomas in fat tissue as well as a few benign and malignant tumours at various sites. Only one liver haemangiosarcoma was noted. All animals exposed to 500 p.p.m. developed tumours; 71 % of the animals given 50 p.p.m. were tumour bearing. The frequency of all tumours, number of tumour foci and size of foci in both groups suggest a dose-dependent carcinogenic effect of vinyl chloride. Haemocoelia due to blood vessel rupture was a common cause of death. Telangiectasis of the liver was also observed in a few animals. The role of fat tissue as well as blood vessel involvement in the pathology of vinyl chloride is discussed.     

Influence of low dietary iron and iron overload on urethan-induced lung tumors in mice.

Weanling male CD-1 mice were fed low iron (7 ppm), control (120 ppm) and iron loaded diets (3000 or 5000 ppm) for 19 weeks. After seven weeks, the mice received 1.5 mg urethan/g ip, and tumor development was evaluated 12 weeks later. The low iron diet increased the incidence of lung adenomas by 86%. The iron loaded diets did not influence adenoma development. Tumor size was unaffected by iron status (p = 0.297). These results indicate that low iron body status promotes tumor development and are inconsistent with the hypothesis that excess iron promotes cancer growth and that low iron protects against tumor growth.     

Survival, immune responses and tissue cyst production in outbred (Swiss white) and inbred (CBA/Ca) strains of mice experimentally infected with Neospora caninum tachyzoites

The present work compared inbred (CBA/Ca) and outbred (Swiss white) strains of mice for their capacity to cope with a Neospora caninum infection and to consistently produce tissue cysts. In each experiment Swiss white and CBA/Ca mice were given three different doses of NC-1 tachyzoites. Lymphoproliferative and humoral responses as well as cytokine production were evaluated eight weeks after infection (PI) whereas tissue cyst production and histopathology were assessed 4, 6 and 10 weeks PI in immunosuppressed mice. Tissue cysts were observed 10 weeks after infection only in CBA/Ca mice receiving the two highest inoculum doses. Furthermore this strain showed the highest specific lymphoproliferative response. A mixed cytokine response with elevated IFN-gamma and fairly low IL-4 and IL-10 secretion was recorded. In both strains, no lesions were observed in the tissues of infected mice. This study indicates that CBA/Ca female mice infected with 5 x 10(6) NC-1 tachyzoites represent a useful model for the study of specific maternal immune responses in pregnant animals.     

The roles of Smad2 and Smad3 in the development of chemically induced skin tumors in mice

Transforming growth factor-beta (TGF-beta) plays a complex role in skin carcinogenesis, acting as a suppressor early in tumor development but later as a promoter. Smad proteins are important intracellular mediators of TGF-beta signaling. To determine the effect of disrupting Smad genes and TGF-beta signaling on chemically induced skin carcinogenesis in mice, transgenic mice heterozygous for Smad2 or Smad3 deletions and wild-type controls were treated with topical dimethylbenzanthracene for 7 months. Tumor multiplicity, type, and degree of differentiation were assessed by histopathology and immunohistochemistry. Smad3(+/-) mice developed significantly fewer tumors than the wild-type group (P < 0.05). This indicated a possible oncogenic function for Smad3 in skin carcinogenesis. Smad2(+/-) mice formed less-differentiated tumors than their wild-type counterparts, supporting a tumor suppressor role for Smad2. There was a significant difference (P < 0.05) in tumor type between Smad2(+/-) and Smad3(+/-) groups, suggesting that Smad2 and Smad3 may regulate different targets.     

Evaluation of data from mitogen studies in CBA mice: comparison of counts per minute, stimulation index and relative proliferation index.

Lymphocyte proliferation assays were conducted on splenic lymphocytes collected from CBA mice that had been exposed to lead acetate or cadmium chloride for 10 weeks. The ability of mitogens concanavalin A and lipopolysaccharide, as well as purified protein derivative, to induce proliferation in vitro in the presence or absence of macrophages was assessed. Data were compared by using counts per minute (cpm), stimulation index, and relative proliferative index. Data varied considerably within treatment groups performed on different days, which is a typical characteristic of mitogen proliferation investigations. According to cpm data, only 3 of 21 treatments were significantly (P less than 0.05) altered when compared with controls. The stimulation indices were highly influenced by background counts and frequently did not correlate with cpm. The relative proliferative index, on the other hand, calculates net cpm, closely corresponds to cpm, compensates for background counts and is affected less by variation than is the stimulation index, and selected cutoff values give a more sensitive measure for determination of altered proliferative responses when statistical procedures are not applicable. Effects of macrophages, carbon dioxide, and bovine fetal serum on lymphocyte transformation are discussed.     

Dietary lutein and fish oil interact to alter atherosclerotic lesions in a Japanese quail model of atherosclerosis

Interactions between concentration of dietary lutein and fish oil in diets on atherosclerosis incidences were studied in a cholesterol-induced-atherosclerosis (CIA) model. CIA Japanese quail were fed a basal diet with three amounts of lutein (0, 25 and 50 mg/kg diet) and two amounts of fish oil (3% and 6%) in a 3 × 2 factorial in five replications. Samples were collected at 24 and 27 weeks of age. Atherosclerosis lesions in the dorsal aorta were measured by histochemistry sectioning. At 27 weeks of age, increasing dietary fish oil content to 6% decreased (p < 0.01) the atherosclerotic lesions only in the 0 mg lutein supplemented groups. At 27 weeks of age, increasing dietary fish oil content to 6% increased the atherosclerotic lesion score when lutein was supplemented at either 25 or 50 mg/kg feed. Aorta and liver lutein content increased (p < 0.01) with increasing dietary lutein content at 27 weeks of age. Increasing dietary fish oil content to 6% increased (p < 0.01) the aorta fat content by twofold and decreased (p < 0.01) the liver fat by 26% at 27 weeks of age. Increasing the dietary fish oil content to 6% increased (p = 0.01) the total PUFA and decreased (p = 0.03) the total mono unsaturated fatty acids content of the aorta at 27 weeks of age. At 27 weeks of age, increasing dietary fish oil content to 6% decreased the amount of TBARS (p = 0.01) and IL-1 mRNA (p < 0.01) only in the 0 mg lutein supplemented groups. Increasing dietary fish oil content to 6% increased the amount of TBARS and IL-1 mRNA of the aorta when lutein was supplemented at either 25 or 50 mg/kg diet. Dietary lutein supplementation decreased atherosclerosis lesions only at low levels of dietary polyunsaturated fatty acids.     

Vitamin E and selenium concentrations in livers of pigs diagnosed with mulberry heart disease.

During a 2-year period from January 1, 1999, to December 31, 2000, 77 diagnoses of mulberry heart disease (MHD) were documented at the Iowa State University Veterinary Diagnostic Laboratory. Mean (+/- SD) liver vitamin E concentrations were lower (P < 0.05) in pigs with MHD (3.12 +/- 1.12 ppm, wet weight) than in pigs that died of causes other than MHD (4.80 +/- 3.2 ppm, wet weight). The majority of the pigs affected with MHD ranged in age from 3 to 7 weeks. Statistical influence of age was found on the concentration of vitamin E (P < 0.01) but not on concentration of selenium in liver in pigs with MHD. Concentrations of vitamin E below 2 ppm were considered deficient. Hepatic vitamin E concentrations below 2 ppm were measured in 25% of the pigs with gross and microscopic lesions of MHD. In contrast, liver selenium concentrations were adequate in all pigs.     

Duration of strain 2308 infection and immunogenicity of Brucella abortus lipopolysaccharide in five strains of mice

A study was conducted to compare immunogenicity of a Brucella abortus lipopolysaccharide (LPS) and the duration of infection in 5 strains of mice. Mice of strains CBA/NJ, BALB/c, CD-1, C3H/HeN, and C3H/HeJ were allotted into 2 large groups (vaccinated with proteinase K-treated LPS or nonvaccinated) and 6 subgroups based on the intervals between challenge exposure to B abortus strain 2308 and the week the response data were obtained. Criteria used in comparing responses between the various strains of mice as well as between vaccinated and nonvaccinated mice were splenomegaly, colony-forming units (CFU) from spleens, and antibody titers. Responses were evaluated at 1, 2, 3, 5, 8, and 12 weeks after challenge exposure. Results indicated that all strains of mice became infected and maintained infection throughout the 12-week period, the percentages of mice infected were significantly (P less than 0.05) less in vaccinated mice for the first 5 weeks after challenge exposure, and there were no direct correlations between increased immunoglobulins (IgM and IgG titers) and reduction in CFU. Vaccinated mice of strains BALB/c, CD-1, C3H/HeN, and C3H/HeJ had increased titers when challenge exposed and also had significantly (P less than 0.05) smaller spleens and lower CFU. Vaccinated CBA/NJ mice did not have marked antibody titers. The overall results indicated that vaccination with LPS offers some initial protection against B abortus strain 2308 infection, but this protection disappears gradually and in various degrees in the 5 strains of mice studied.     

Modifications of azoxymethane-induced carcinogenesis and 90-day oral toxicities of 2-tetradecylcyclobutanone as a radiolytic product of stearic acid in F344 rats

A 90-day oral toxicity test in rats was performed to evaluate the toxicity of 2-tetradecylcyclobutanone (2-tDCB), a unique radiolytic product of stearic acid. Six-week-old male and female F344 rats (n=15/group) were given 2-tDCB at concentrations of 0, 12, 60 and 300 ppm in a powder diet for 13 weeks. Slight dose-dependent increases in serum total protein and albumin in male rats were found, but these changes were not considered to be a toxic effect. The fasting, but not non-fasting, blood glucose levels of the male rats in the 300 ppm group and female rats in the 60 and 300 ppm groups were lower than those of the controls. Gas chromatography-mass spectrometry analysis showed dose-dependent accumulation of 2-tDCB in adipose tissue, notably in males. Next, we performed an azoxymethane (AOM)-induced two-stage carcinogenesis study. After injection of 6-week-old male F344 rats (n=30/group) once a week for 3 weeks, the animals received 2-tDCB at concentrations of 0, 10, 50 and 250 ppm in a powder diet for 25 weeks. The incidences of colon tumors for the 2-tDCB dosages were 34%, 45%, 40% and 37%, respectively, and were not statistically significant. These data suggest that 2-tDCB shows no toxic or tumor-modifying effects under the present conditions, and that the no-observed-adverse-effect level for 2-tDCB is 300 ppm in both sexes, equivalent to 15.5 mg/kg b.w./day in males and 16.5 mg/kg b.w./day in females.     

Induction of interferon production in mice by delipidated whole cells and fractions of the aerobic corynebacterium, Corynebacterium catarrhalis

The i.v. or i.p. injection of delipidated whole cells of an aerobic Corynebacterium, designated as C. catarrahalis, resulted in the production of a low titre of interferon in mice. Two fractions, a particulate fraction, designated as CBA p40, and a soluble fraction, designated as CBA LS, could be isolated from the delipidated whole cells and were found to lead to the formation of more or less high interferon levels according to the route of administration. Furthermore, the CBA p40 fraction, when injected i.p., elicited the production of a maximum titre of interferon at the 24th hour (viral-like interferon).     

Fetal loss and hyposulfataemia in pregnant NaS1 transporter null mice

Sulfate is important for growth and development, and is supplied from mother to fetus throughout pregnancy. We used NaS1 sulfate transporter null (Nas1(-/-)) mice to investigate the role of NaS1 in maintaining sulfate homeostasis during pregnancy and to determine the physiological consequences of maternal hyposulfataemia on fetal, placental and postnatal growth. We show that maternal serum (≤0.5 mM), fetal serum (<0.1 mM) and amniotic fluid (≤0.5 mM) sulfate levels were significantly lower in pregnant Nas1(-/-) mice when compared with maternal serum (?2.0 mM), fetal serum (?1.5 mM) and amniotic fluid (?1.7 mM) sulfate levels in pregnant Nas1(+/+) mice. After 12 days of pregnancy, fetal reabsorptions led to markedly reduced (by ≥50%) fetal numbers in Nas1(-/-) mice. Placental labyrinth and spongiotrophoblast layers were increased (by ?140%) in pregnant Nas1(-/-) mice when compared to pregnant Nas1(+/+) mice. Birth weights of progeny from female Nas1(-/-) mice were increased (by ?7%) when compared to progeny of Nas1(+/+) mice. These findings show that NaS1 is essential to maintain high maternal and fetal sulfate levels, which is important for maintaining pregnancy, placental development and normal birth weight.     

The effects of dietary T-2 toxin on acute herpes simplex virus type 1 infection in mice

Young male white Swiss mice were fed control diet or diet supplemented with 20 or 10 parts per million (ppm) of T-2 toxin for two or three weeks. These mice then were inoculated with herpes simplex virus type 1 (HSV-1) (9.6 x 10(6) plaque forming units) intraperitoneally. To compare the effects of T-2 toxin against a known immunosuppressive drug, cyclophosphamide was injected intraperitoneally at 150 mg/kg, 24 hours after treatment with HSV-1, into mice fed the control diet. Mice were necropsied and tissues were collected for microscopic and virologic examination. White Swiss mice which consumed a daily diet containing 20 ppm of T-2 toxin for two or three weeks were highly susceptible to HSV-1 infection and 27 of 36 (75%) died as a result of extensive hepatic and adrenal necrosis. Although HSV-1 was isolated from livers and brains of mice fed 20 ppm of T-2 toxin for two or three weeks, there was little or no inflammatory response found in the adrenals, livers, spinal cords, brains, or ganglia. The necrotizing encephalomyelitis observed in control mice was absent. High levels of dietary T-2 toxin appeared to be more immunosuppressive than cyclophosphamide because only one mouse died after treatment with HSV-1 and cyclophosphamide. Mice treated with cyclophosphamide had changes in brain, spinal cord, spleens, thymus, and bone marrow which were similar to those fed 20 ppm of T-2 toxin and infected with HSV-1, however, liver lesions were much less severe. HSV-1-infected mice on a diet with 10 ppm T-2 toxin had lesions of intermediate severity when compared with HSV-1-infected mice fed a diet with 20 ppm T-2 toxin and HSV-1-infected mice on control diets. Necrosis was less extensive in the livers and adrenals. The infrequent isolation of virus from liver and brain was consistent with the lack of intranuclear inclusion bodies and a more marked inflammatory response. Ten ppm of dietary T-2 toxin only depressed bone marrow and splenic red pulp to a mild or moderate degree. This may have enhanced the necrotizing encephalomyelitis observed in mice killed on days 6 and 8 after HSV-1 infection. Liver lesions were mild and those of the adrenals were moderate in mice fed control diet. The rare isolation of HSV-1 from the liver and brain and the findings of a moderate to severe necrotizing encephalomyelitis in these mice was consistent with an essentially functional immune system.     

Effect of gluconic acid on piglet growth performance, intestinal microflora, and intestinal wall morphology

Gluconic acid (GA) derives from the incomplete oxidation of glucose by some Gluconobacter strains. When fed to nonruminant animals, GA is only poorly absorbed in the small intestine and is primarly fermented to butyric acid in the lower gut. This study investigated the effect of GA on in vitro growth response and metabolism of swine cecal microflora and on animal growth performance, intestinal wall morphology, and intestinal microflora. During a 24-h in vitro cecal fermentation, total gas production and maximum rate of gas production were increased by GA (linear, P < 0.001). Ammonia in cecal liquor was reduced by GA after 4, 8, and 24 h of fermentation (quadratic, P < 0.01). After 24 h of fermentation, total short-chain fatty acids, acetic acid, propionic acid, n-butyric acid, acetic to propionic acid ratio, and acetic + butyric to propionic acid ratio were linearly increased by GA (P < 0.001). In the in vivo study, 48 piglets were divided into 4 groups and housed in individual cages for 6 wk. Piglets received a basal diet with a) no addition (control) or with GA addition at b) 3,000 ppm, c) 6,000 ppm, or d) 12,000 ppm. After 6 wk, 4 animals per treatment were killed, and samples of intestinal content and mucosa were collected. Compared with control, GA tended to increase average daily gain (+13 and +14% for GA at 3,000 and 6,000 ppm, respectively; P of the model = 0.11; quadratic, P < 0.05). Daily feed consumption and gain to feed ratio were not influenced by GA. Intestinal counts of clostridia, enterobacteriaceae, and lactic acid bacteria were not affected by GA. Gluconic acid tended to increase total short-chain fatty acids in the jejunum (+174, +87, and +74% for GA at 3,000, 6,000, and 12,000 ppm, respectively; P of the model = 0.07; quadratic, P = 0.07). Morphological evaluation of intestinal mucosa from jejunum, ileum, and cecum did not show any significant differences among treatments. This study showed that feeding GA influences the composition and activity of the intestinal microflora and may improve growth performance of piglets after weaning.     

Effect of growth in cell cultures and strain on virulence of Mycoplasma hyopneumoniae for swine

In an attempt to develop better methods for consistent induction of pneumonia in naturally born swine, using cultures of Mycoplasma hyopneumoniae, fifty 6-week-old, naturally born pigs from a respiratory disease-free herd were used in 3 trials. Pigs inoculated with Mycoplasma hyopneumoniae strain 232 (passage 21) grown for 1 passage or 5 passages in Eagle minimal essential medium plus 20% porcine serum, with or without human lung fibroblasts, had a mean (+/- SD) value range between 5.4 +/- 3.6 and 9.2 +/- 2.1% of consolidated lung area. In the second trial, pigs inoculated 1, 2, or 3 days in succession with strain 232 grown in Eagle medium or Friis mycoplasmal medium with 20% porcine serum had between 5.1 +/- 7 and 8.7 +/- 4.3% of consolidated lung area. In the third trial, virulence of Mycoplasma hyopneumoniae strains 144L (p27), 11 (p26), J (p60), and 232 (p27) grown in Friis mycoplasmal medium was compared. Pigs inoculated with those strains had 5.1 +/- 4.1, 2.6 +/- 3.1, 0, and 4.3 +/- 4% of consolidated lung area, respectively. Significant differences were not found in consolidated lung area among groups in trials 1 and 2, and among groups of pigs inoculated with M hyopneumoniae strains 144L, 11, and 232 in trial 3. Pneumonia was not detected in pigs inoculated with strain J in trial 3.