A one-year longitudinal study of enterohemorrhagic Escherichia coli O157 fecal shedding in a beef cattle herd.

Bovines are the primary reservoir of enterohemorrhagic Escherichia coli (EHEC) O157:H7 and the main source of its transmission to humans. Here, we present a one-year longitudinal study of fecal shedding of E. coli O157. E. coli O157 obtained from recto-anal mucosal samples were characterized by multiplex PCR. The E. coli O157 prevalence ranged from 0.84% in July to 15.25% in November. The confinement within pens resulted in prevalence of 11%. Most animals (61.86%; 75/118) shed E. coli O157 at least in one sampling occasion. Of the positive animals, 82.19%, 16.44%, and 1.37% were stx positive on one, two and three sampling occasions, respectively. All the E. coli O157 isolated strains carried the genes eae and rfbO157, whereas 11%, 33% and 56% contained stx1, stx2 and stx1/stx2, respectively. The stx1/stx2 and stx2 types were significantly higher during the grazing and finishing periods, respectively, in comparison with the rearing and grazing periods. The presence of stx2a subtype was evident in four isolates, whereas stx2c was present in at least seven. However, both subtypes were present simultaneously in two isolates. The stx1/stx2c, stx1/stx2d and stx1/stx2NT genotypes occurred in 24, 2 and 15 isolates, respectively. The simultaneous occurrence of stx1 and stx2c significantly increased during grazing. Some cases of within-pen and between-pen transmission occurred throughout the study. Contagion levels during in-field grazing were higher than during permanent confinement in the pens. Thus, the individual patterns of shedding varied depending on the proportion of animals shedding the bacteria within pens and the time of shedding.

Somatic embryogenesis in Asparagus officinalis L. cv. Argenteuil: interactions between genotype, explant type and growth regulators on callus induction, growth and embryogenic differentiation.

Callus induction, growth and embryogenic differentiation were studied in two selected genotypes of Asparagus officinalis L. cv. Argenteuil, to develop a protocol for somatic embryogenesis. Two experiments were carried out. In the first, four explant types (spear sections and lateral buds, both of in vivo and in vitro origin), and three levels of 2,4-D (1.5, 5 and 10 mg.l-1) and two of KIN (0 and 1 mg.l-1) added to MS basal medium, were tested during the three initial culture stages (90 d period). All factors were included in one factorial design to statistically analyze interaction effects. Interactions between genotype, explant type and time of culture initiation were significant for callus induction and growth during the two initial culture stages. The addition of kinetin enhanced callus induction and growth, and high levels of 2,4-D depressed callus growth. The average embryogenic differentiation was < 2% overall (11% with the best factor combination). In the second experiment, another explant type (bud clusters) was tested; the average embryogenic differentiation was 1.9% (best combination: 5.6%). For the two genotypes studied, the best factor combinations were the culture of in vivo lateral buds or bud clusters on MS basal medium with 1.5 mg.l-1 2,4-D and 1 mg.l-1 KIN.

Effects of previous suppressive anthelmintic treatments on subsequent nematode infection in fattening cattle in Argentina.

The effect of previous suppressive anthelmintic treatments after weaning on parasitological parameters and weight gain of cattle was studied in the Pampeana region of Argentina. The study was carried out at two grazing fattening periods: April 1995/July 1996 and April 1997/July 1998. During both periods, 60 weaned calves that grazed contaminated pastures, were divided into three groups during the first part of the periods: GY1 group was treated every 2 weeks with doramectin while GY2 and GY3 groups remained untreated. During the second part of the periods, from October onwards GY1 and GY2 remained untreated and GY3 was treated every 2 weeks. In this second period two new groups of 20 weaning young calves were added: TG (treated every 2 weeks) and UG (untreated). Egg counts (EPG), larval cultures, pasture larval counts, serum pepsinogen (Pep) and live weight gain (LWG) were recorded monthly. Ostertagia, Cooperia, Trichostrongylus and Haemonchus were the predominant genera. Despite low levels of previous infection during the first part of the period, slight differences of EPG between GY1 (P<0.09) or UG (P<0.05) and GY2 were detected in the second part of the fattening period in 1995/1996. In 1997/1998 moderate infection levels during the first part of the period were observed. During the second part of this period, GY1 and UG showed higher (P<0.001) EPG than GY2, and only GY3 and TG had (P<0.05) lower Pep levels. Also, during the second part of 1997/1998, LWG responses of GY3 were higher (P<0.001) than those of GY1 and GY2. Live weight gain of GY2 exceeded GY1 by 10.7kg (P<0.006). Higher EPG and lower LWG of GY1 suggest that suppressive treatments negatively affected the level of resistance to infection of yearlings, but these effects were influenced by previous levels of nematode infection. The lack of differences between yearling (GY1) and calves (UG) groups suggest that, under the conditions of this study, there was no evidence that resistance to infection and the related parameters are influenced by the age.

Somatic embryogenesis in Asparagus officinalis L. cv. Argenteuil: interactions between genotype, explant type and growth regulators on callus induction, growth and embryogenic differentiation.

Callus induction, growth and embryogenic differentiation were studied in two selected genotypes of Asparagus officinalis L. cv. Argenteuil, to develop a protocol for somatic embryogenesis. Two experiments were carried out. In the first, four explant types (spear sections and lateral buds, both of in vivo and in vitro origin), and three levels of 2,4-D (1.5, 5 and 10 mg.l-1) and two of KIN (0 and 1 mg.l-1) added to MS basal medium, were tested during the three initial culture stages (90 d period). All factors were included in one factorial design to statistically analyze interaction effects. Interactions between genotype, explant type and time of culture initiation were significant for callus induction and growth during the two initial culture stages. The addition of kinetin enhanced callus induction and growth, and high levels of 2,4-D depressed callus growth. The average embryogenic differentiation was < 2

overall (11

with the best factor combination). In the second experiment, another explant type (bud clusters) was tested; the average embryogenic differentiation was 1.9

(best combination: 5.6

). For the two genotypes studied, the best factor combinations were the culture of in vivo lateral buds or bud clusters on MS basal medium with 1.5 mg.l-1 2,4-D and 1 mg.l-1 KIN.