Reference | Hasman2006 (10206)

The purpose of this study was to examine whether the copper concentration (175 ppm versus 6 ppm) used for the growth promotion of piglets is able to select for copper resistance among E. faecium isolates in vivo and to test whether this could result in coselection of macrolide- and glycopeptide-resistant bacteria. Ten tcrB-negative (copper-sensitive) and 10 tcrB-positive (copper-resistant) E. faecium strains were used in this study. Twenty-four specific-pathogen-free Large White pigs of 8 weeks of age, obtained from the experimental swine herd of AFSSA were divided into two groups consisting of four experimental units (pens 1, 2, 3, and 4), with each unit containing six animals. The 24 pigs were obtained from three sows and were randomized (balanced) before the experiment. Pens 1 and 2 were replicates of the same treatment, as were pens 3 and 4. Pigs in pens 1 and 2 were fed a low-copper feed both prior to and during the whole experiment. Pigs in pens 3 and 4 were fed a low-copper feed up to the inoculation day (day 0) and a high-copper feed just after inoculation. The mean animal weights of the animals in the four pens on inoculation day (day 0) were 21.5 to 22.9 kg. Very strict biosecurity measures were implemented in order to avoid contamination of the pigs. Pigs were euthanized on days 35 to 37 postinoculation, and lesions were observed. The animals did not receive any treatment with any antibiotics prior to or during the feeding experiment. The feed offered to the animals before inoculation was not supplemented with copper and consisted of a 16% protein, low-copper feed (7.3% [weight/dry weight] minerals, 92.7% [weight/dry weight] organic material, and 6.4 mg of copper/kg of body weight [dry weight, approximately 5.2 mg/kg 0.26 mg/kg when corrected for water]). Immediately after bacterial inoculation (day 0), animals in pens 1 and 2 were fed the same feed as before the inoculation, while the animals in pens 3 and 4 were shifted to a high-copper diet containing the same 16% protein feed but with copper sulfate added to a final concentration of 208 mg/kg of copper (dry weight, approximately 179 mg/kg 17 mg/kg). The animals in the four pens were individually fed 20 ml of the mixture of copper-sensitive and copper-resistant E. faecium strains described above (approximately 109 bacteria of each strain) to ensure that all animals received the same inoculum size.

Fecal samples were collected from each pig 0, 7, 14, 21, and 28 days after inoculation for isolation of E. faecium.

AST Method: Disk Diffusion

Reference explicitly reports AST breakpoints: False

Reference reports using a MIC table: False