College of Animal Science, Inner Mongolia Agricultural University, Hohhot, Inner Mongolia, China.
J Appl Microbiol. 2011 Aug;111(2):511-23. doi: 10.1111/j.1365-2672.2011.05066.x. Epub 2011 Jun 23.
To characterize class 1 integrons and resistance genes in tetracycline-resistant Escherichia coli originating from beef cattle subtherapeutically administered chlortetracycline (A44), chlortetracycline and sulfamethazine (AS700), or no antimicrobials (control).
Tetracycline-resistant E. coli (control, n = 111; AS700, n = 53; A44, n = 40) were studied. Class 1 integrons, inserted gene cassettes and the presence of other antimicrobial resistance genes, as well as phylogenetic analysis, were performed by PCR, restriction enzyme analysis and sequencing. Susceptibilities to 11 antimicrobials were conducted on all isolates. Prevalence of class 1 integrase was higher (P < 0·001) in isolates from AS700 (33%) and A44 (28%) steers as compared to control (7%). Most integron gene cassettes belonged to the aad or dfr families. Correlations were found between the tet(A) gene and the genetic elements sul1 (r = 0·44), aadA1 (r = 0·61), cat (r = 0·58) and intI1(r = 0·37). Both closely and distantly related isolates harboured integrons with identical gene cassette arrays.
Subtherapeutic administration of chlorotetracycline alone or in combination with sulfamethazine may select for class 1 integrons in bovine tetracycline-resistant E. coli isolates. Vertical spread and horizontal transfer are responsible for the dissemination of a particular type of class 1 integron, but this study could not differentiate if this phenomenon occurred within or outside of the feedlot. Tetracycline-resistant E. coli strains with sul1 and tet(A) genes were more likely to harbour class 1 integrons.
Subtherapeutic use of chlortetracycline and sulfamethazine may promote the presence of class 1 integrons in tetracycline-resistant E. coli isolated from feedlot cattle.
研究亚治疗剂量给予金霉素（A44）、金霉素和磺胺嘧啶（AS700）或不使用抗生素（对照）的牛源四环素耐药大肠杆菌中类 1 整合子和耐药基因的特征。
研究了四环素耐药大肠杆菌（对照，n=111；AS700，n=53；A44，n=40）。通过 PCR、限制性内切酶分析和测序检测类 1 整合子、插入基因盒和其他抗生素耐药基因的存在，并进行了分析。对所有分离株进行了 11 种抗生素的药敏试验。AS700（33%）和 A44（28%）牛源分离株中类 1 整合酶的检出率高于对照（7%）（P<0·001）。大多数整合子基因盒属于 aad 或 dfr 家族。tet(A)基因与遗传元件 sul1（r=0·44）、aadA1（r=0·61）、cat（r=0·58）和 intI1（r=0·37）之间存在相关性。密切相关和较远的分离株都携带具有相同基因盒阵列的整合子。
单独或联合使用金霉素和磺胺嘧啶的亚治疗剂量可能会选择牛源四环素耐药大肠杆菌分离株中的类 1 整合子。垂直传播和水平转移是导致特定类型类 1 整合子传播的原因，但本研究无法区分这种现象是在饲料场内还是场外发生。携带 sul1 和 tet(A)基因的四环素耐药大肠杆菌菌株更有可能携带类 1 整合子。
金霉素和磺胺嘧啶的亚治疗使用可能会促进饲料场牛源四环素耐药大肠杆菌中类 1 整合子的存在。
