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Abstract：
BACKGROUND: This study analyzed the genetic traits and fitness costs of vancomycin-resistant Enterococcus faecium (VREfm) blood isolates carrying Tn1546-type transposons harboring the vanA operon.
METHODS: All E. faecium blood isolates were collected from eight general hospitals in South Korea during one-year study period. Antimicrobial susceptibility testing and vanA and vanB PCR were performed. Growth rates of E. faecium isolates were determined. The vanA-positive isolates were subjected to whole genome sequencing and conjugation experiments.
RESULTS: Among 308 E. faecium isolates, 132 (42.9%) were positive for vanA. All Tn1546-type transposons harboring the vanA operon located on the plasmids, but on the chromosome in seven isolates. The plasmids harboring the vanA operon were grouped into four types; two types of circular, nonconjugative plasmids (Type A, n = 50; Type B, n = 46), and two types of putative linear, conjugative plasmids (Type C, n = 16; Type D, n = 5). Growth rates of vanA-positive E. faecium isolates were significantly lower than those of vanA-negative isolates (P < 0.001), and reduction in growth rate under vancomycin pressure was significantly larger in isolates harboring putative linear plasmids than in those harboring circular plasmids (P = 0.020).
CONCLUSIONS: The possession of vanA operon was costly to bacterial hosts in antimicrobial-free environment, which provide evidence for the importance of reducing vancomycin pressure for prevention of VREfm dissemination. Fitness burden to bacterial hosts was varied by type and size of the vanA operon-harboring plasmid.
METHODS: All E. faecium blood isolates were collected from eight general hospitals in South Korea during one-year study period. Antimicrobial susceptibility testing and vanA and vanB PCR were performed. Growth rates of E. faecium isolates were determined. The vanA-positive isolates were subjected to whole genome sequencing and conjugation experiments.
RESULTS: Among 308 E. faecium isolates, 132 (42.9%) were positive for vanA. All Tn1546-type transposons harboring the vanA operon located on the plasmids, but on the chromosome in seven isolates. The plasmids harboring the vanA operon were grouped into four types; two types of circular, nonconjugative plasmids (Type A, n = 50; Type B, n = 46), and two types of putative linear, conjugative plasmids (Type C, n = 16; Type D, n = 5). Growth rates of vanA-positive E. faecium isolates were significantly lower than those of vanA-negative isolates (P < 0.001), and reduction in growth rate under vancomycin pressure was significantly larger in isolates harboring putative linear plasmids than in those harboring circular plasmids (P = 0.020).
CONCLUSIONS: The possession of vanA operon was costly to bacterial hosts in antimicrobial-free environment, which provide evidence for the importance of reducing vancomycin pressure for prevention of VREfm dissemination. Fitness burden to bacterial hosts was varied by type and size of the vanA operon-harboring plasmid.
摘要：
背景：这项研究分析了携带带有vanA操纵子的Tn1546型转座子的耐万古霉素屎肠球菌（VREfm）血液分离株的遗传性状和适应性成本。
方法：在一年的研究期间，从韩国的8家综合医院收集所有屎肠球菌的血液分离株。进行了药敏试验以及vanA和vanBPCR。测定屎肠球菌分离株的生长速率。对vanA阳性分离株进行全基因组测序和缀合实验。
结果：在308个屎肠球菌分离株中，132（42.9%）为vanA阳性。所有Tn1546型转座子都带有位于质粒上的vanA操纵子，而是在7个分离株的染色体上.带有vanA操纵子的质粒分为四种类型；两种类型的圆形，非共轭质粒(A型，n=50；B型，n=46),和两种类型的假定线性，共轭质粒（C型，n=16；类型D，n=5)。vanA阳性屎肠杆菌的生长速率显著低于vanA阴性菌株(P<0.001),并且在万古霉素压力下生长速率的降低在带有假定的线性质粒的分离株中明显大于带有环状质粒的分离株（P=0.020）。
结论：在无抗菌环境中，拥有vanA操纵子对细菌宿主来说是昂贵的，这为降低万古霉素压力对预防VREfm传播的重要性提供了证据。细菌宿主的适应性负担因vanA操纵子携带质粒的类型和大小而异。
方法：在一年的研究期间，从韩国的8家综合医院收集所有屎肠球菌的血液分离株。进行了药敏试验以及vanA和vanBPCR。测定屎肠球菌分离株的生长速率。对vanA阳性分离株进行全基因组测序和缀合实验。
结果：在308个屎肠球菌分离株中，132（42.9%）为vanA阳性。所有Tn1546型转座子都带有位于质粒上的vanA操纵子，而是在7个分离株的染色体上.带有vanA操纵子的质粒分为四种类型；两种类型的圆形，非共轭质粒(A型，n=50；B型，n=46),和两种类型的假定线性，共轭质粒（C型，n=16；类型D，n=5)。vanA阳性屎肠杆菌的生长速率显著低于vanA阴性菌株(P<0.001),并且在万古霉素压力下生长速率的降低在带有假定的线性质粒的分离株中明显大于带有环状质粒的分离株（P=0.020）。
结论：在无抗菌环境中，拥有vanA操纵子对细菌宿主来说是昂贵的，这为降低万古霉素压力对预防VREfm传播的重要性提供了证据。细菌宿主的适应性负担因vanA操纵子携带质粒的类型和大小而异。
