Department of Laboratory Medicine and Research Institute of Bacterial Resistance, Gangnam Severance Hospita, l, Yonsei University College of Medicine, 211 Eonju-Ro, Gangnam-Gu, Seoul, 06273, South Korea.
Department of Companion Animal Health and Science, Silla University, Busan, South Korea.
Ann Clin Microbiol Antimicrob. 2024 Jul 8;23(1):62. doi: 10.1186/s12941-024-00722-2.
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.
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.
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).
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.
本研究分析了携带 vanA 操纵子的 Tn1546 型转座子的万古霉素耐药粪肠球菌（VREfm）血源分离株的遗传特征和适应度代价。
在为期一年的研究期间，从韩国的八所综合医院收集了所有粪肠球菌血源分离株。进行了抗菌药物敏感性试验和 vanA 和 vanB PCR。测定了粪肠球菌分离株的生长率。对 vanA 阳性分离株进行了全基因组测序和接合实验。
在 308 株粪肠球菌分离株中，有 132 株（42.9%）对 vanA 呈阳性。所有携带 vanA 操纵子的 Tn1546 型转座子均位于质粒上，但在 7 株分离株的染色体上。携带 vanA 操纵子的质粒分为四种类型；两种类型的圆形、非接合性质粒（A 型，n = 50；B 型，n = 46），两种类型的推定线性、接合性质粒（C 型，n = 16；D 型，n = 5）。vanA 阳性粪肠球菌分离株的生长率明显低于 vanA 阴性分离株（P < 0.001），携带推定线性质粒的分离株在万古霉素压力下的生长率下降明显大于携带圆形质粒的分离株（P = 0.020）。
在无抗菌药物环境中，携带 vanA 操纵子对细菌宿主是有代价的，这为减少万古霉素压力以预防 VREfm 传播提供了证据。携带 vanA 操纵子的质粒的类型和大小对细菌宿主的适应度负担不同。
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