Department of Diagnostic Medicine/Pathobiology, Kansas State University, Manhattan, Kansas 66506-5606, USA.
Foodborne Pathog Dis. 2010 Sep;7(9):1089-97. doi: 10.1089/fpd.2010.0540.
High concentration of copper, fed as copper sulfate, is often used to increase growth rates in swine. Bacteria exposed to copper may acquire resistance, and in Enterococcus faecium and Enterococcus faecalis, a plasmid-borne transferable copper resistance (tcrB) gene that confers copper resistance has been reported. Our objectives were to determine the occurrence of tcrB in fecal enterococci from weaned piglets fed diets with a normal supplemental level (16.5 ppm) or an elevated supplemental level (125 ppm) of copper and to determine the association of tcrB with copper, erythromycin, and vancomycin resistance. A total of 323 enterococcal isolates were examined and 15 (4.6%) isolates (14 E. faecium and 1 E. faecalis) were positive for tcrB. Fifteen tcrB-positive and 15 randomly chosen tcrB-negative isolates from piglets fed the normal supplemental level of copper were tested for erm(B), tet(M), vanA, and vanB genes and susceptibilities to copper, erythromycin, tetracyclines, and vancomycin. All tcrB-positive and -negative isolates contained erm(B) and tet(M), but not vanA and vanB. The mean minimum inhibitory concentration of copper for tcrB-positive (21.1 mM) was higher (p < 0.001) compared with tcrB-negative isolates (6.1 mM). All isolates were resistant to erythromycin and tetracyclines and susceptible to vancomycin. The transferability of the tcrB gene from tcrB-positive strains to tcrB-negative strains was demonstrated by conjugation. The potential link between tcrB and antibiotic resistance genes and the propensity of enterococci to transfer tcrB to other strains raises the possibility that copper supplementation may exert selection pressure for antibiotic-resistant enterococci. This study is the first report on the occurrence of the tcrB gene in enterococci isolated from swine in the United States.
高浓度的铜（通常以硫酸铜的形式添加）常用于提高猪的生长速度。暴露于铜的细菌可能会产生耐药性，在屎肠球菌和粪肠球菌中，已报道了一种可转移的铜耐药性（tcrB）质粒基因，该基因赋予铜耐药性。我们的目标是确定在饲喂正常补充水平（16.5 ppm）或高补充水平（125 ppm）铜的断奶仔猪粪便肠球菌中是否存在 tcrB，并确定 tcrB 与铜、红霉素和万古霉素耐药性的相关性。共检测了 323 株肠球菌分离株，其中 15 株（4.6%）分离株（14 株屎肠球菌和 1 株粪肠球菌）为 tcrB 阳性。从饲喂正常补充水平铜的仔猪中选择 15 株 tcrB 阳性和 15 株随机选择的 tcrB 阴性分离株，检测 erm（B）、tet（M）、vanA 和 vanB 基因，并检测对铜、红霉素、四环素和万古霉素的敏感性。所有 tcrB 阳性和阴性分离株均含有 erm（B）和 tet（M），但不含有 vanA 和 vanB。tcrB 阳性分离株的铜最小抑菌浓度平均值（21.1 mM）明显高于（p < 0.001）tcrB 阴性分离株（6.1 mM）。所有分离株均对红霉素和四环素耐药，对万古霉素敏感。通过接合试验证实了 tcrB 基因从 tcrB 阳性株向 tcrB 阴性株的可转移性。tcrB 与抗生素耐药基因之间的潜在联系以及肠球菌向其他菌株转移 tcrB 的倾向，增加了铜补充可能对抗生素耐药肠球菌产生选择压力的可能性。本研究是首次在美国猪源肠球菌中报道 tcrB 基因的存在。
