摘要

作为抗生素替代品的益生菌被广泛用作牛和猪生产系统中性能益处的饲料添加剂。在益生菌中所含的细菌种类中，屎肠球菌是常见的。抗菌药物耐药性（AMR），特别是多药耐药性是肠球菌中常见的特征，因为它们倾向于获得抗药性并水平转移AMR基因。另外，屎肠球菌是机会性病原体，而在美国，它是第二种最常见的医院病原体。目前还没有关于美国牛和猪使用的益生菌产品中所含屎肠球菌的AMR和毒力潜力的公开研究。因此，我们的目标是确定表型敏感性或对抗菌剂，毒力基因（asa1，gelE，cylA，esp和hyl）的抗性，并评估从商业产品中分离的屎肠球菌的遗传多样性。购买了用于牛（n = 13）和猪（n = 9）的22种可商购的基于屎肠球菌的益生菌产品，分离出屎肠球菌并证实了物种。通过使用全国抗微生物耐药监测系统革兰氏阳性灵敏度平板（CMV3AGPF）的微量肉汤稀释法进行抗微生物药物敏感性测试以确定最小抑制浓度，并根据临床实验室和标准研究所的指南将菌株分类为易感性或抗性。来自7种产品（猪3种和牛4种）的屎肠球菌对测试的16种抗菌剂具有泛易感性。来自15种产品（猪6种和牛9种）的菌株表现出对至少一种抗微生物剂的抗性，并且高比例的菌株对林可霉素（10/22）有抗性，其次是四环素（4/22），达托霉素（4/22 ），环丙沙星（4/22），卡那霉素（3/22）和青霉素（2/22）。四个菌株是多重耐药的，具有从3到6个抗菌剂或类别的抗性表型。没有任何屎肠球菌菌株对任何测试的毒力基因都呈阳性。通过脉冲场凝胶电泳（PFGE）分型确定22个屎肠球菌菌株之间的克隆关系。观察到22种菌株共有10种PFGE模式，并且来自不同益生菌产品的一些菌株具有相同的（100％骰子相似性）PFGE模式。总之，一些商业益生菌中的屎肠球菌菌株对医疗上重要的抗菌剂显示出AMR，但没有一种含有毒力基因。

Probiotics, an antibiotic alternative, are widely used as feed additives for performance benefits in cattle and swine production systems. Among bacterial species contained in probiotics, Enterococcus faecium is common. Antimicrobial resistance (AMR), particularly multidrug resistance, is a common trait among enterococci because of their propensity to acquire resistance and horizontally transfer AMR genes. Also, E. faecium is an opportunistic pathogen, and in the United States, it is the second most common nosocomial pathogen. There has been no published study on AMR and virulence potential in E. faecium contained in probiotic products used in cattle and swine in the United States. Therefore, our objectives were to determine phenotypic susceptibilities or resistance to antimicrobials, virulence genes (asa1, gelE, cylA, esp, and hyl) and assess genetic diversity of E. faecium isolated from commercial products. Twenty-two commercially available E. faecium-based probiotic products used in cattle (n = 13) and swine (n = 9) were procured and E. faecium was isolated and species confirmed. Antimicrobial susceptibility testing to determine minimum inhibitory concentrations was done by micro-broth dilution method using National AntimicrobialResistance Monitoring Systems Gram-positive Sensititre panel plate (CMV3AGPF), and categorization of strains as susceptible or resistant was as per Clinical Laboratory and Standards Institute's guidelines. E. faecium strains from 7 products (3 for swine and 4 for cattle) were pan-susceptible to the 16 antimicrobials tested. Strains from 15 products (6 for swine and 9 for cattle) exhibited resistance to at least one antimicrobial and a high proportion of strains was resistant to lincomycin (10/22), followed by tetracycline (4/22), daptomycin (4/22), ciprofloxacin (4/22), kanamycin (3/22), and penicillin (2/22). Four strains were multidrug resistant, with resistant phenotypes ranging from 3 to 6 antimicrobials or class. None of the E. faecium strains were positive for any of the virulence genes tested. The clonal relationships among the 22 E. faecium strains were determined by pulsed-field gel electrophoresis (PFGE) typing. A total of 10 PFGE patterns were observed with 22 strains and a few of the strains from different probiotic products had identical (100% Dice similarity) PFGE patterns. In conclusion, the E. faecium strains in a few commercial probiotics exhibited AMR to medically-important antimicrobials, but none contained virulence genes.

https://www.ncbi.nlm.nih.gov/pubmed/29584914