Molecular characterisation of bovine faecal Escherichia coli shows persistence of defined ampicillin resistant strains and the presence of class 1 integrons on an organic beef farm

Antimicrobial use is heavily restricted on organic farms; however, few studies have been conducted to investigate the impact this has on the epidemiology of resistance in pathogenic and commensal bacteria. We investigated the persistence of antimicrobial resistant Escherichia coli within an organic beef herd over a period of 28 months. Faecal samples collected monthly from three calf cohorts and annually from adult cattle and environmental samples, were screened for the presence of ampicillin, apramycin and nalidixic acid resistant E. coli. The prevalence of ampicillin resistance ranged from 27.3 to 40.7% in the annual herd and environmental samplings (n=22-55) and was greater in the calf cohorts, with a peak cohort prevalence of >47% in all 3 years (n=16-18). Apramycin and nalidixic acid resistant E. coli were rare. Pulsed-field gel electrophoresis (PFGE) identified 10 main genotype groups within the herd, with evidence of strain transmission between different livestock groups, animal species and years. Multiple resistance was found in >44% of isolates tested, with ampicillin, neomycin, sulphamethoxazole and tetracycline carriage the commonest phenotype identified. PCR detected the presence of class 1 integrons in <5% of resistant isolates, 6/7 of which were of cattle origin. These data demonstrate that ampicillin resistant E. coli was common on the farm despite restricted antimicrobial use, although strain diversity was low. Persistence of defined genotype groups was observed between years, together with the transmission of resistant strains between different animal species on the farm.     

Host–strain mediated selection for an effective nitrogen-fixing symbiosis between Trifolium spp. and Rhizobium leguminosarum biovar trifolii

We have previously reported significant strain–host incompatibility between the microsymbiont Rhizobium leguminosarum biovar trifolii and Trifolium spp. related to geographic and phenological barriers. Additionally, we have shown that an effective symbiosis between strains of R. l. trifolii and clover was established despite the soil harbouring ineffective R. l. trifolii capable of nodulating the host. We termed this “selection” for effective symbiosis. This paper reports glasshouse-based experiments to validate and further explore this in situ selection phenomenon. The effect of cell density and strain ratio at the time of inoculation, as well as soil pH, were investigated on two hosts (Trifolium purpureum and Trifolium polymorphum) that were each exposed to one microsymbiont capable and one incapable of N₂ fixation. In co-inoculation experiments at a cell density of 10⁴ cells/mL, each host nodulated solely with its effective strain, even when this strain was outnumbered 100-fold by the ineffective strain. However, the selection process ceased when the effective strain was outnumbered 1000-fold. At higher basal cell concentrations of 10⁵–10⁸ cells/mL, selection for WSM1325 to form effective nodulation on T. purpureum was evident, but was significantly reduced as the ratio of ineffective cells in the inoculum increased above 4-fold. The results indicate that the selection mechanism is highly dependent on the basal rhizobial cell density. Soil pH did not significantly alter the process, and both strains grew at similar rates and formed nodules at similar rates. A preliminary investigation into the genetic backgrounds of WSM1325 and WSM2304 revealed that although their 16S rRNA sequences were identical, they have considerable differences in their symbiotic and chromosomal replicons through examination of atpD, GSII and nodD sequences.     

Scale-specific land cover thresholds for conservation of stream invertebrate communities in agricultural landscapes

Context

In agricultural landscapes, riparian forests are used as a management tool to protect stream ecosystems from agricultural activities. However, the ability of managers to target stream protection actions is limited by incomplete knowledge of scale-specific effects of agriculture in riparian corridor and catchment areas.

Objectives

We evaluated scale-specific effects of agricultural cover in riparian corridor and catchment areas on stream benthic macroinvertebrate (BMI) communities to develop cover targets for agricultural landscapes.

Methods

Sixty-eight streams assigned to three experimental treatments (Forested Riparian, Agricultural Riparian, Agricultural Catchment) were sampled for BMIs. Ordination and segmented regression were used to assess impacts of agriculture on BMI communities and detect thresholds for BMI community metrics.

Results

BMI communities were not associated with catchment agricultural cover where the riparian corridor was forested, but were associated with variation in catchment agriculture where riparian forests had been converted to agriculture. Trait-based metrics showed threshold responses at greater than 70% agricultural cover in the catchment. Increasing agriculture in the riparian corridor was associated with less diverse and more tolerant BMI communities. Eight metrics exhibited threshold responses ranging from 45 to 75% agriculture in the riparian corridor.

Conclusions

Riparian forest effectively buffered streams from agricultural activity even where catchment agriculture exceeds 80%. We recommend managers prioritize protection of forested riparian corridors and that restore riparian corridors where agricultural cover is near identified thresholds be a secondary priority. Adoption of catchment management actions should be effective where the riparian corridor has been converted to agriculture.

     

Chaining and Burning Modifies Vegetation Structure,Fuel, and Post-Disturbance Sprouting Capacity

Prescribed fire and/or mechanical methods can be used to modify the quantity, continuity, and/or spatial arrangement of flammable fuel. Yet the consequences of fuel management, both in terms of ecological outcomes and in facilitating improved fire management, often are poorly documented. In the global biodiversity hotspot of southwest Western Australia, chaining and burning is a novel technique for manipulating fuels. Vegetation first is dislodged using a chain, then after a period of curing, burnt. We tested whether combining two disturbance events in this way results in different vegetation structure postfire than only burning, and whether the postfire sprouting capacity of community-dominant Eucalyptus spp. is compromised. Both chained and burnt and only burnt treatments had much less leaf litter and vegetation > 25 cm high than long-unburnt vegetation, indicating a fire management benefit of fuel modification. Chained and burnt strips had a threefold reduction in standing dead vegetation compared to only burnt samples. The stem number of Eucalyptus spp. was reduced by 20% in chained and burnt strips compared to only burnt vegetation, indicating that consecutive disturbances reduce resilience and might render sprouters vulnerable to subsequent disturbances. Balancing the fire management benefits of chaining and burning with the ecological consequences is a significant challenge facing land managers in this fire-prone landscape.     

Unilateral uterine torsion secondary to an inflammatory endometrial polyp in the bitch

A 9-year-old bitch was presented because of lethargy and abdominal distension. Abdominal ultrasound revealed an enlarged, fluid-filled uterus and associated mass. Subsequent exploratory laparotomy revealed unilateral uterine torsion involving the mass. Recovery following ovariohysterectomy was uneventful and the histopathological diagnosis was of a benign endometrial inflammatory polyp. Reports of uterine torsion in the English-language literature are reviewed to identify factors associated with the incidence of uterine torsion. The aetiology of the cystic endometrial hyperplasia/pyometra complex and its possible role in the development of inflammatory polypoid lesions in the bitch is also discussed.     

Dose and release pattern of anabolic implants affects growth of finishing beef steers across days on feed

Four experiments evaluated the effect of implant dose and release pattern on performance and carcass traits of crossbred beef steers. In Exp. 1, steers (4 to 7 pens/treatment; initial BW = 315 kg) were fed an average of 174 d. Treatments were 1) no implant (NI); 2) Revalor-S [120 mg of trenbolone acetate (TBA) and 24 mg of estradiol 17β (E(2)); REV-S]; 3) Revalor-IS followed by REV-S (cumulatively 200 mg of TBA and 40 mg of E(2); reimplanted at 68 to 74 d; REV-IS/S); and 4) Revalor-XS (200 mg of TBA and 40 mg of E(2); REV-X). Carcass-adjusted final BW was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (610, 609, and 598 kg, respectively). Daily DMI did not differ (P > 0.10) among the 3 implants, but carcass-adjusted G:F was greater (P < 0.05) for REV-X and REV-IS/S than for REV-S (0.197 and 0.195 vs. 0.188). Both HCW and LM area were greater (P < 0.05) for REV-X and REV-IS/S than for REV-S. Marbling scores were greatest (P < 0.05) for REV-S and least (P < 0.05) for REV-IS/S; REV-X was intermediate to NI and REV-IS/S. In Exp. 2, steers (10 pens/treatment; initial BW = 391 kg) were fed 131 d, with treatments of REV-S, REV-IS/S (reimplanted at 44 to 47 d), and REV-X. Carcass-adjusted final BW (598 kg), ADG (1.6 kg), DMI (9.4 kg), G:F (0.17), and HCW did not differ (P > 0.10) among treatments. The percentage of Choice was less (P < 0.05) and percentage of Select greater (P < 0.05) for REV-IS/S than for REV-S and REV-X. In Exp. 3, steers (10 pens/treatment; initial BW = 277 kg) were fed 197 d and received either REV-IS/S (reimplanted at 90 to 103 d) or REV-X. Carcass-adjusted final BW (625 vs. 633 kg) and ADG (1.81 vs. 1.76 kg) were greater (P < 0.05) for REV-X-implanted steers. Daily DMI did not differ, but G:F tended (P < 0.10) to be increased and HCW was greater (P < 0.05) for REV-X than for REV-IS/S. In Exp. 4, steers (8 pens/treatment; initial BW = 238 kg) were fed 243 d and received either REV-IS/S (reimplanted at 68 to 71 d) or REV-X. Carcass-adjusted final BW (612 kg), ADG (1.54 kg), DMI (7.55), and G:F (0.21) did not differ (P > 0.10) for REV-IS/S and REV-X-implanted steers. Carcass traits did not differ among implants, but the percentage of Choice carcasses was greater (P < 0.05) and percentage of Select was less (P < 0.05) for REV-X than for REV-IS/S. These data indicate that when TBA/E(2) dose is equal, the altered release rate of REV-X can improve performance and quality grade, but these effects depend on duration of the feeding period and timing of initial and terminal implants.     

Effects of bacterial lipopolysaccharide injection on white blood cell counts, hematological variables, and serum glucose, insulin, and cortisol concentrations in ewes fed low- or high-protein diets

Bacterial lipopolysaccharide endotoxins (LPS) elicit inflammatory responses reflective of acute bacterial infection. We determined if feeding ewes high-CP (15.5%) or low-CP (8.5%) diets for 10 d altered inflammatory responses to an intravenous bolus of 0 (control), 0.75 (L75), or 1.50 (L150) μg of LPS/kg of BW in a 2 × 3 factorial arrangement of treatments (n = 5/treatment). Rectal temperatures, heart and respiratory rates, blood leukocyte concentrations, and serum cortisol, insulin, and glucose concentrations were measured for 24 h after an LPS bolus (bolus = 0 h). In general, rectal temperatures were greater (P ≤ 0.05) in control ewes fed high CP, but LPS increased (P ≤ 0.05) rectal temperatures in a dose-dependent manner at most times between 2 and 24 h after the bolus. Peak rectal temperatures in L75 and L150 occurred 4 h after the bolus. A monophasic, dose-independent increase (P ≤ 0.023) in serum cortisol occurred from 0.5 to 24 h after the bolus, with peak cortisol at 4 h. Serum insulin was increased (P ≤ 0.016) by LPS in a dose-dependent manner from 4 to 24 h after the bolus. Insulin did not differ between control ewes fed high- and low-CP diets but was greater (P < 0.001) in L75 ewes fed low CP compared with high CP and in L150 ewes fed high CP compared with low CP. Increased insulin was not preceded by increased serum glucose. Total white blood cell concentrations were not affected (P ≥ 0.135) by LPS, but the neutrophil and monocyte fractions of white blood cells were increased (P ≤ 0.047) by LPS at 12 and 24 h and at 24 h after the bolus, respectively, and the lymphocyte fraction was increased (P = 0.037) at 2 h and decreased (P ≤ 0.006) at 12 and 24 h after the bolus. Red blood cell and hemoglobin concentrations and hematocrit (%) were increased (P ≤ 0.022) by LPS at 2 and 4 h after the bolus. Rectal temperatures and serum glucose were greater (P ≤ 0.033) in ewes fed a high-CP diet before LPS injection, but these effects were lost at and within 2.5 h of the bolus, respectively. Feeding high-CP diets for 10 d did not reduce inflammation in ewes during the first 24 h after LPS exposure but may benefit livestock by preventing acute insulin resistance when endotoxin exposure is mild.     

Strategies for bacterial tagging and gene expression in plant-host colonization studies

Bacteria are extraordinarily diverse microorganisms with a huge potential to benefit environmental and agricultural systems. Comprehensive studies in complex habitats such as soils and plants have led to the development of genetic tools to evaluate gene expression and bacterial colonization under controlled or environmental conditions and to obtain genetically engineered organisms for environmental release. In addition, current advances in genomic and metagenomic research will add to the number of genes with potential for biotechnological applications, which will require the development of appropriate genetic systems to fulfill their potential for both industrial and agricultural applications. The aim of the present review is to assess the approaches and recent progress in vector design and genetic tools to study and manipulate plant-bacterial interactions, as well as strategies to construct genetically modified strains for environmental release.