Provenance & quality
Faecal samples were taken by members of staff from Rothamsted Research North Wyke. In the laboratory one gram of faecal material was aseptically transferred to nine ml of sterile Ringers (Oxoid, Basingstoke, UK) and appropriate serial 10-fold dilutions were made. An aliquot (0.1 ml) was plated in duplicate on to Membrane Lactose Glucuronide Agar (MLGA) (Oxoid) and spread across the surface of the agar using a disposal plastic spreader (VWR). Antibiotics were added to the MLGA at suitable concentrations after autoclaving and prior to pouring the plates. Antibiotics were added at the following rates; 16 mg/l for tetracycline and cephalexin, 1.0 mg/l marbofloxacin, 8 mg/l meropenem. All plates were allowed to air dry prior to inversion and incubation, at 44.5 ◦C (±0.2 ◦C) for 18–24 h. Colonies were counted, after incubation, and reported as E.coli colony forming units (CFU) per gram fresh weight and also on a dry weight basis. All colony counts were further transformed by log to base 10.
Gravimetric moisture content of faecal samples, approximately 50 g of faecal material was accurately weighed into a pre-weighed silver foil container and dried in an oven at 105 ◦C, until constant weight. To calculate % dry matter: 100 – (((fresh wt.-Dry wt.) /(fresh wt.))*100), effectively 100 – moisture content.
The establishment licence under which the experiment was conducted was XA11784A2 and the project licence was P592D2677.
Data was collected for the NERC funded “Does the potential for AMR selection differ between common UK cattle grazing systems?” NE/N019792/1.