Amachawadi Raghavendra G, Scott H Morgan, Vinasco Javier, Tokach Mike D, Dritz Steve S, Nelssen Jim L, Nagaraja Tiruvoor G
1 Departments of Diagnostic Medicine and Pathobiology, Kansas State University , Manhattan, Kansas.
2 Department of Veterinary Pathobiology, College of Veterinary Medicine & Biomedical Sciences, Texas A&M University , College Station, Texas.
Foodborne Pathog Dis. 2015 Aug;12(8):670-8. doi: 10.1089/fpd.2015.1961. Epub 2015 Jun 2.
Heavy metals, such as copper, are increasingly supplemented in swine diets as an alternative to antibiotics to promote growth. Enterococci, a common gut commensal, acquire plasmid-borne, transferable copper resistance (tcrB) gene-mediated resistance to copper. The plasmid also carried resistance genes to tetracyclines and macrolides. The potential genetic link between copper and antibiotic resistance suggests that copper supplementation may exert a selection pressure for antimicrobial resistance. Therefore, a longitudinal study was conducted to investigate the effects of in-feed copper, chlortetracycline, and tylosin alone or in combination on the selection and co-selection of antimicrobial-resistant enterococci. The study included 240 weaned piglets assigned randomly to 6 dietary treatment groups: control, copper, chlortetracycline, tylosin, copper and chlortetracycline, and copper and tylosin. Feces were collected before (day 0), during (days 7, 14, 21), and after (days 28 and 35) initiating treatment, and enterococcal isolates were obtained from each fecal sample and tested for genotypic and phenotypic resistance to copper and antibiotics. A total of 2592 enterococcal isolates were tested for tcrB by polymerase chain reaction. The overall prevalence of tcrB-positive enterococci was 14.3% (372/2592). Among the tcrB-positive isolates, 331 were Enterococcus faecium and 41 were E. faecalis. All tcrB-positive isolates contained both erm(B) and tet(M) genes. The median minimum inhibitory concentration of copper for tcrB-negative and tcrB-positive enterococci was 6 and 18 mM, respectively. The majority of isolates (95/100) were resistant to multiple antibiotics. In conclusion, supplementing copper or antibiotics alone did not increase copper-resistant enterococci; however, supplementing antibiotics with copper increased the prevalence of the tcrB gene among fecal enterococci of piglets.
重金属，如铜，作为抗生素的替代品越来越多地添加到猪的日粮中以促进生长。肠球菌是一种常见的肠道共生菌，可获得质粒携带的、可转移的铜抗性（tcrB）基因介导的对铜的抗性。该质粒还携带对四环素和大环内酯类的抗性基因。铜与抗生素抗性之间潜在的遗传联系表明，添加铜可能对抗菌药物抗性产生选择压力。因此，进行了一项纵向研究，以调查饲料中单独添加铜、金霉素和泰乐菌素或联合添加对耐抗菌药物肠球菌的选择和共选择的影响。该研究包括240头断奶仔猪，随机分配到6个日粮处理组：对照组、铜组、金霉素组、泰乐菌素组、铜和金霉素组以及铜和泰乐菌素组。在开始处理前（第0天）、处理期间（第7、14、21天）和处理后（第28和35天）收集粪便，从每个粪便样本中分离出肠球菌，并检测其对铜和抗生素的基因型和表型抗性。通过聚合酶链反应对总共2592株肠球菌分离株进行tcrB检测。tcrB阳性肠球菌的总体患病率为14.3%（372/2592）。在tcrB阳性分离株中，331株为粪肠球菌，41株为屎肠球菌。所有tcrB阳性分离株均同时含有erm（B）和tet（M）基因。tcrB阴性和tcrB阳性肠球菌对铜的最小抑菌浓度中位数分别为6和18 mM。大多数分离株（95/100）对多种抗生素耐药。总之，单独添加铜或抗生素不会增加耐铜肠球菌；然而，铜与抗生素联合添加会增加仔猪粪便肠球菌中tcrB基因的患病率。
