Tsuka Takeshi, Ozaki Hiroichi, Saito Daisuke, Murase Toshiyuki, Okamoto Yoshiharu, Azuma Kazuo, Osaki Tomohiro, Ito Norihiko, Murahata Yusuke, Imagawa Tomohiro
Joint Department of Veterinary Medicine, Faculty of Agriculture, Tottori University, Tottori, Japan.
Front Vet Sci. 2021 May 7;8:659222. doi: 10.3389/fvets.2021.659222. eCollection 2021.
CTX-M-2-producing () has not received much attention in animal husbandry compared with (), a major reservoir of extended-spectrum β-lactamase (ESBL) genes. Bacteriological examinations of 1,466 mastitic milk samples between October 2012 and December 2014 were conducted. Ninety-five isolates (total prevalence: 6.5%) and 81 isolates (total prevalence: 5.5%) were obtained. Seventeen isolates obtained from 15 animals reared on 11 farms and 9 isolates obtained from 9 animals reared on the same farm were phenotypically confirmed to be ESBL producers. All nine ESBL-producing isolates were obtained from one farm between June and November 2013 and related to a significantly ( < 0.05) higher monthly prevalence of mild mastitis (in June, August, September, October, and November 2013). Pulsed-field gel electrophoresis (PFGE) patterns of ESBL-producing isolates were distinguished from each other by more than 6-band differences except for two isolates from two animals, whereas all nine isolates showed an identical PFGE pattern. Transferability of the gene was found in 14 and 9 isolates by conjugation analysis. Of these isolates, the gene was detected on plasmids belonging to the incompatibility (Inc) groups P and N derived from five and nine isolates, respectively, although the plasmids from the remaining nine were untypeable. All the transconjugants exhibited elevated minimum inhibitory concentrations of ampicillin, cefotaxime, and ceftiofur compared with those in the wild-type, recipient strain. Restriction fragment length polymorphism analysis demonstrated that the IncN plasmids extracted from eight of nine transconjugants, which received resistance against β-lactams from , showed an identical I digestion pattern. These results suggest that the CTX-M-2-producing strain with the above-mentioned characteristics may have clonally spread within a farm, whereas the gene in possibly disseminated among the farms through different plasmids. Thus, monitoring of ESBL genes, including the gene, among causative agents of bacterial mastitis in cows can help to develop relevant treatments and control practices.
与作为超广谱β-内酰胺酶（ESBL）基因主要储存库的大肠杆菌相比，产CTX-M-2的停乳链球菌在畜牧业中未受到太多关注。对2012年10月至2014年12月期间的1466份患乳房炎乳样进行了细菌学检查。获得了95株停乳链球菌分离株（总流行率：6.5%）和81株大肠杆菌分离株（总流行率：5.5%）。从11个农场饲养的15头动物中获得的17株停乳链球菌分离株和从同一农场饲养的9头动物中获得的9株大肠杆菌分离株经表型确认产ESBL。所有9株产ESBL的大肠杆菌分离株均于2013年6月至11月从一个农场获得，并且与轻度乳房炎的月流行率显著较高（P<0.05）（在2013年6月、8月、9月、10月和11月）有关。产ESBL的停乳链球菌分离株的脉冲场凝胶电泳（PFGE）图谱，除了来自两只动物的两株分离株外，彼此之间的差异超过6条带，而所有9株大肠杆菌分离株显示出相同的PFGE图谱。通过接合分析在14株停乳链球菌和9株大肠杆菌分离株中发现了CTX-M-2基因的可转移性。在这些分离株中，CTX-M-2基因分别在来自5株停乳链球菌和9株大肠杆菌的属于不相容（Inc）群P和N的质粒上检测到，尽管其余9株大肠杆菌的质粒无法分型。与野生型受体菌株相比，所有转接合子对氨苄西林、头孢噻肟和头孢噻呋的最低抑菌浓度均升高。限制性片段长度多态性分析表明，从9株转接合子中的8株提取的IncN质粒，这些转接合子从大肠杆菌获得了对β-内酰胺类的抗性，并显示出相同的I消化模式。这些结果表明，具有上述特征的产CTX-M-2停乳链球菌菌株可能已在一个农场内克隆传播，而大肠杆菌中的CTX-M-2基因可能通过不同质粒在农场间传播。因此，监测奶牛细菌性乳房炎病原体中的ESBL基因，包括CTX-M-2基因，有助于制定相关的治疗和控制措施。
