School of Laboratory Medicine and Life Science, Wenzhou Medical University, Wenzhou, Zhejiang Province, China.
Department of Clinical Laboratory, The First Affiliated Hospital of Wenzhou Medical University, Wenzhou, Zhejiang Province, China.
Int J Antimicrob Agents. 2017 Jul;50(1):29-34. doi: 10.1016/j.ijantimicag.2017.02.010. Epub 2017 Apr 26.
Fosfomycin in combination with various antibiotics represents an excellent clinically efficacious regimen for the treatment of urinary tract infections (UTIs) caused by extended-spectrum β-lactamase (ESBL)-producing Escherichia coli. Underlying mechanisms of fosfomycin resistance remain largely uncharacterised. To investigate the antibacterial efficacy of fosfomycin against ESBL-producing E. coli, 356 non-repetitive ESBL-producing E. coli clinical isolates were collected from urine specimens from patients with UTI in Wenzhou, China, from January 2011 to December 2015. Antimicrobial sensitivity testing indicated that 6.7% (24/356) of the ESBL-producing E. coli strains were resistant to fosfomycin. The fosA3 gene encoding a fosfomycin-modifying enzyme was detected in 20 isolates by PCR and sequencing, alone or in combination with other ESBL determinants. Conjugation experiments and Southern blotting demonstrated that 70% (14/20) of the fosA3-positive isolates possessed transferable plasmids (ca. 54.2 kb) co-harbouring the ESBL resistance gene bla and the fosfomycin resistance gene fosA3. Among the four fosfomycin-resistant fosA3-negative E. coli isolates, three contained amino acid substitutions (Ile28Asn and Phe30Leu in MurA and Leu297Phe in GlpT). The results indicate that presence of the fosA3 gene is the primary mechanism of fosfomycin resistance in ESBL-producing E. coli isolates in Wenzhou, China. In addition, a plasmid (ca. 54.2 kb) co-harbouring fosA3 and bla genes is horizontally transferable. Furthermore, a low degree of homology in the fosfomycin-resistant E. coli was confirmed using multilocus sequence typing (MLST), suggesting that there is no obvious phenomenon of clonal dissemination.
磷霉素与各种抗生素联合使用，为治疗产超广谱β-内酰胺酶（ESBL）大肠埃希菌引起的尿路感染（UTI）提供了一种非常有效的临床方案。但目前对磷霉素耐药的潜在机制仍知之甚少。为了研究磷霉素对产 ESBL 大肠埃希菌的抗菌效果，我们从中国温州 2011 年 1 月至 2015 年 12 月的尿路感染患者尿液标本中收集了 356 株非重复产 ESBL 大肠埃希菌临床分离株。药敏试验表明，6.7%（24/356）的产 ESBL 大肠埃希菌对磷霉素耐药。PCR 和测序结果显示，20 株菌携带编码磷霉素修饰酶的 fosA3 基因，单独或与其他 ESBL 决定簇一起存在。接合实验和 Southern 印迹证实，70%（14/20）的 fosA3 阳性分离株携带可转移质粒（约 54.2 kb），该质粒同时携带 ESBL 耐药基因 bla 和磷霉素耐药基因 fosA3。在 4 株 fosA3 阴性磷霉素耐药大肠埃希菌分离株中，有 3 株含有 MurA 中的氨基酸取代（Ile28Asn 和 Phe30Leu）和 GlpT 中的 Leu297Phe）。结果表明，fosA3 基因的存在是中国温州产 ESBL 大肠埃希菌对磷霉素耐药的主要机制。此外，fosA3 和 bla 基因共存的质粒（约 54.2 kb）可水平转移。进一步通过多位点序列分型（MLST）证实，磷霉素耐药大肠埃希菌的同源性较低，表明没有明显的克隆传播现象。
