Antimicrobial resistance in dairy slurry tanks: A critical point for measurement and control

Waste from dairy production is one of the largest sources of contamination from antimicrobial resistant bacteria (ARB) and genes (ARGs) in many parts of the world. However, studies to date do not provide necessary evidence to inform antimicrobial resistance (AMR) countermeasures. We undertook a detailed, interdisciplinary, longitudinal analysis of dairy slurry waste. The slurry contained a population of ARB and ARGs, with resistances to current, historical and never-used on-farm antibiotics; resistances were associated with Gram-negative and Gram-positive bacteria and mobile elements (ISEcp1, Tn916, Tn21-family transposons). Modelling and experimental work suggested that these populations are in dynamic equilibrium, with microbial death balanced by fresh input. Consequently, storing slurry without further waste input for at least 60 days was predicted to reduce ARB spread onto land, with > 99 % reduction in cephalosporin resistant Escherichia coli. The model also indicated that for farms with low antibiotic use, further reductions are unlikely to reduce AMR further. We conclude that the slurry tank is a critical point for measurement and control of AMR, and that actions to limit the spread of AMR from dairy waste should combine responsible antibiotic use, including low total quantity, avoidance of human critical antibiotics, and choosing antibiotics with shorter half-lives, coupled with appropriate slurry storage.

More sustainable vegetable oil: Balancing productivity with carbon storage opportunities

Intensive cultivation and post-harvest vegetable oil production stages are major sources of greenhouse gas (GHG) emissions. Variation between production systems and reporting disparity have resulted in discordance in previous emissions estimates. The aim of this study was to assess global systems-wide variation in GHG emissions resulting from palm, soybean, rapeseed and sunflower oil production. Such an analysis is critical to understand the implications of meeting increasing edible oil demand. To achieve this, we performed a unified re-analysis of life cycle input data from diverse palm, soybean, rapeseed, and sunflower oil production systems, from a saturating search of published literature. The resulting dataset reflects almost 6000 producers in 38 countries, and is representative of over 71% of global vegetable oil production. Across all oil crop systems, median GHG emissions were 3.81 kg CO2e per kg refined oil. Crop specific median emissions ranged from 2.49 kg CO2e for rapeseed oil to 4.25 kg CO2e for soybean oil per kg refined oil. Determination of the carbon cost of agricultural land occupation revealed that carbon storage potential in native compared to agricultural land cover drives variation in production GHG emissions, and indicates that expansion of production in low carbon storage potential land, whilst reforesting areas of high carbon storage potential, could reduce net GHG emissions whilst boosting productivity. Nevertheless, there remains considerable scope to improve sustainability within current production systems, including through increasing yields whilst limiting application of inputs with high carbon footprints, and in the case of palm oil through more widespread adoption of methane capture technologies in processing stages.

Analysing reduced tillage practices within a bio-economic modelling framework

Sustainable intensification of agricultural production systems will require changes in farm practice. Within arable cropping systems, reducing the intensity of tillage practices (e.g. reduced tillage) potentially offers one such sustainable intensification approach. Previous researchers have tended to examine the impact of reduced tillage on specific factors such as yield or weed burden, whilst, by definition, sustainable intensification necessitates a system-based analysis approach. Drawing upon a bio-economic optimisation model, 'MEETA', we quantify trade-off implications between potential yield reductions, reduced cultivation costs and increased crop protection costs. We extend the MEETA model to quantify farm-level net margin, in addition to quantifying farm-level gross margin, net energy, and greenhouse gas emissions. For the lowest intensity tillage system, zero tillage, results demonstrate financial benefits over a conventional tillage system even when the zero tillage system includes yield penalties of 0-14.2% (across all crops). Average yield reductions from zero tillage literature range from 0 to 8.5%, demonstrating that reduced tillage offers a realistic and attainable sustainable intensification intervention, given the financial and environmental benefits, albeit that yield reductions will require more land to compensate for loss of calories produced, negating environmental benefits observed at farm-level. However, increasing uptake of reduced tillage from current levels will probably require policy intervention; an extension of the recent changes to the CAP ('Greening') provides an opportunity to do this.

Mathematical modelling of antimicrobial resistance in agricultural waste highlights importance of gene transfer rate

Antimicrobial resistance is of global concern. Most antimicrobial use is in agriculture; manures and slurry are especially important because they contain a mix of bacteria, including potential pathogens, antimicrobial resistance genes and antimicrobials. In many countries, manures and slurry are stored, especially over winter, before spreading onto fields as organic fertilizer. Thus, these are a potential location for gene exchange and selection for resistance. We develop and analyse a mathematical model to quantify the spread of antimicrobial resistance in stored agricultural waste. We use parameters from a slurry tank on a UK dairy farm as an exemplar. We show that the spread of resistance depends in a subtle way on the rates of gene transfer and antibiotic inflow. If the gene transfer rate is high, then its reduction controls resistance, while cutting antibiotic inflow has little impact. If the gene transfer rate is low, then reducing antibiotic inflow controls resistance. Reducing length of storage can also control spread of resistance. Bacterial growth rate, fitness costs of carrying antimicrobial resistance and proportion of resistant bacteria in animal faeces have little impact on spread of resistance. Therefore, effective treatment strategies depend critically on knowledge of gene transfer rates.

Multidrug resistant, extended spectrum β-lactamase (ESBL)-producing Escherichia coli isolated from a dairy farm

Escherichia coli strains were isolated from a single dairy farm as a sentinel organism for the persistence of antibiotic resistance genes in the farm environment. Selective microbiological media were used to obtain 126 E. coli isolates from slurry and faeces samples from different farm areas. Antibiotic resistance profiling for 17 antibiotics (seven antibiotic classes) showed 57.9% of the isolates were resistant to between 3 and 15 antibiotics. The highest frequency of resistance was to ampicillin (56.3%), and the lowest to imipenem (1.6%), which appeared to be an unstable phenotype and was subsequently lost. Extended spectrum β-lactamase (ESBL) resistance was detected in 53 isolates and blaCTX-M, blaTEM and blaOXA genes were detected by PCR in 12, 4 and 2 strains, respectively. Phenotypically most isolates showing resistance to cephalosporins were AmpC rather than ESBL, a number of isolates having both activities. Phenotypic resistance patterns suggested co-acquisition of some resistance genes within subsets of the isolates. Genotyping using ERIC-PCR demonstrated these were not clonal, and therefore co-resistance may be associated with mobile genetic elements. These data show a snapshot of diverse resistance genes present in the E. coli population reservoir, including resistance to historically used antibiotics as well as cephalosporins in contemporary use.

Straw use and availability for second generation biofuels in England

Meeting EU targets for renewable transport fuels by 2020 will necessitate a large increase in bioenergy feedstocks. Although deployment of first generation biofuels has been the major response to meeting these targets they are subject to wide debate on their sustainability leading to the development of second generation technologies which use lignocellulosic feedstocks. Second generation biofuel can be subdivided into those from dedicated bioenergy crops (DESGB), e.g. miscanthus, or those from co-products (CPSGB) such as cereal straw. Potential supply of cereal straw as a feedstock for CPSGB's is uncertain in England due to the difficulty in obtaining data and the uncertainty in current estimates. An on-farm survey of 249 farms (Cereal, General Cropping and Mixed) in England was performed and linked with Farm Business Survey data to estimate current straw use and potential straw availability. No significant correlations between harvested grain and straw yields were found for wheat and oilseed rape and only a weak correlation was observed for barley. In England there is a potential cereal straw supply of 5.27 Mt from arable farm types; 3.82 Mt are currently used and 1.45 Mt currently chopped and incorporated. If currently chopped and incorporated cereal straw from arable farm types was converted into bioethanol, this could represent 1.5% of the UK petrol consumption by energy equivalence. The variations in regional straw yields (t ha^-1) have a great effect on the England supply of straw and the potential amount of bioethanol that can be produced.

Prospects for arable farm uptake of Short Rotation Coppice willow and miscanthus in England

Biomass will play a role in the UK meeting EU targets on renewable energy use. Short Rotation Coppice (SRC) and miscanthus are potential biomass feedstocks; however, supply will rely on farmer willingness to grow these crops. Despite attractive crop establishment grants for dedicated energy crops (DECs) in the UK, uptake remains low. Drawing on results from an on-farm survey with 244 English arable farmers, 81.6% (87.7%) of farmers would not consider growing miscanthus (SRC), while respectively, 17.2% (11.9%) would consider growing and 1.2% (0.4%) were currently growing these crops. Farmer age, location, land ownership, farm type, farm size and farmer education level were not significant factors in determining acceptance of DECs. The main reasons cited for not growing DECs were impacts on land quality, lack of appropriate machinery, commitment of land for a long period of time, time to financial return and profitability. Reasons cited for willingness to grow DECs included land quality, ease of crop management, commitment of land for a long period of time, and profitability. Farmers cited a range of 'moral' (e.g. should not be using land for energy crops when there is a shortage of food), land quality, knowledge, profit and current farming practice comments as reasons for not growing DECs, while those willing to grow DECs cited interest in renewable energy, willingness to consider new crops, and low labour needs as rationale for their interest. Farm business objectives indicated that maximising profit and quality of life were most frequently cited as very important objectives. Previous research in the UK indicates that farmers in arable areas are unlikely to convert large areas of land to DECs, even where these farmers have an interest and willingness to grow them. Assuming that those farmers interested in growing DECs converted 9.29% (average percentage of arable land set-aside between 1996 and 2005) of their utilised agricultural area to these crops, 50,700 ha and 89,900 ha of SRC and miscanthus would, respectively, be grown on English arable farms. While farm business objectives were not identified as key determinants of DEC acceptance, enhanced information exchange through extension agents, providing market security and considering land reversion grants post-production are potential policy considerations.

Phenotypic and genotypic analysis of bacteria isolated from three municipal wastewater treatment plants on tetracycline-amended and ciprofloxacin-amended growth media

AIMS

The goal of this study was to determine the antimicrobial susceptibility of bacteria isolated from three municipal wastewater treatment plants.

METHODS AND RESULTS

Numerous bacterial strains were isolated from three municipal wastewater treatment facilities on tetracycline- (n=164) and ciprofloxacin-amended (n=65) growth media. These bacteria were then characterized with respect to their resistance to as many as 10 different antimicrobials, the presence of 14 common genes that encode resistance to tetracycline, the presence of integrons and/or the ability to transfer resistance via conjugation. All of the characterized strains exhibited some degree of multiple antimicrobial resistance, with nearly 50% demonstrating resistance to every antimicrobial that was tested. Genes encoding resistance to tetracycline were commonly detected among these strains, although intriguingly the frequency of detection was slightly higher for the bacteria isolated on ciprofloxacin-amended growth media (62%) compared to the bacteria isolated on tetracycline-amended growth media (53%). Class 1 integrons were also detected in 100% of the queried tetracycline-resistant bacteria and almost half of the ciprofloxacin-resistant strains. Conjugation experiments demonstrated that at least one of the tetracycline-resistant bacteria was capable of lateral gene transfer.

CONCLUSIONS

Our results demonstrate that multiple antimicrobial resistance is a common trait among tetracycline-resistant and ciprofloxacin-resistant bacteria in municipal wastewater.

SIGNIFICANCE AND IMPACT OF THE STUDY

These organisms are potentially important in the proliferation of antimicrobial resistance because they appear to have acquired multiple genetic determinants that confer resistance and because they have the potential to laterally transfer these genetic determinants to strains of clinical importance.

Three-dimensional Euclidean nets from two-dimensional hyperbolic tilings: kaleidoscopic examples

We present a method for geometric construction of periodic three-dimensional Euclidean nets by projecting two-dimensional hyperbolic tilings onto a family of triply periodic minimal surfaces (TPMSs). Our techniques extend the combinatorial tiling theory of Dress, Huson & Delgado-Friedrichs to enumerate simple reticulations of these TPMSs. We include a taxonomy of all networks arising from kaleidoscopic hyperbolic tilings with up to two distinct tile types (and their duals, with two distinct vertices), mapped to three related TPMSs, namely Schwarz's primitive (P) and diamond (D) surfaces, and Schoen's gyroid (G).