目的：
虽然已经认为CTX-M型超广谱β-内酰胺酶（ESBL）基因blaCTX-M主要由抗生素抗性质粒携带，但是在先前的研究中已经报道了具有染色体定位的blaCTX-M的大肠杆菌。 。本研究旨在表征染色体定位的blaCTX-M转座单位及其周围序列在日本医院获得的大肠杆菌分离株产ESBL中的遗传结构。

方法：
在该研究中，检查了总共81种产ESBL的大肠杆菌分离物。通过S1核酸酶消化的脉冲场凝胶电泳（PFGE）和Southern印迹杂交以及PCR扩增的DNA片段的测序分析证实了染色体定位的blaCTX-M的存在。

结果：
在22个检测的81个大肠杆菌分离株（27.2％）中确认了染色体定位的blaCTX-M，分别测定了染色体定位的blaCTX-M-14的5和4位点类型，并确定了-15。在22个大肠杆菌分离株中，15个分离株（68.2％）具有单个染色体定位的blaCTX-M，可能是由于质粒blaCTX-M单一转座到染色体上。在分离株N0057的情况下，将blaCTX-M-15转座单位从质粒转移到两个不同的染色体区域。此外，在分离株N0211，N0214，N01127，N1682和N1753中观察到已经存在的染色体定位的blaCTX-M-14向其他染色体区域的“复发”转座;因此，这些分离株具有两个染色体定位的blaCTX-M-14拷贝。

结论：
考虑到其中发生“复发”转座的分离株（N0211，N0214，N01127，N1682和N1753）在PFGE分析中具有遗传相关性，我们的数据表明blaCTX-M在CTX-M型ESBL-染色体上积累的可能性。产生大肠杆菌。

OBJECTIVES:
Although it has been regarded that CTX-M type extended-spectrum β-lactamase (ESBL) gene, blaCTX-M, is mainly carried by antibiotic-resistance plasmids, Escherichia coli-possessing chromosomally-located blaCTX-M has been reported in previous studies. This study aimed to characterize the genetic structures of chromosomally-located blaCTX-M transposition unit and its surrounding sequence in E. coli isolates-producing ESBL which were obtained in a Japanese hospital.

METHODS:
In this study, total of 81 ESBL-producing E. coli isolates were examined. Existence of chromosomally-located blaCTX-M were confirmed by S1 nuclease-digested pulsed-field gel electrophoresis (PFGE) and the Southern blot hybridization, and by sequencing analysis of PCR-amplified DNA fragments.

RESULTS:
Chromosomally-located blaCTX-M was confirmed in 22 of the examined 81 E. coli isolates (27.2%), 5 and 4 location types of the chromosomally-located blaCTX-M-14, and -15 were determined, respectively. Among the 22 E. coli isolates, 15 isolates (68.2%) possessed single chromosomally-located blaCTX-M, probably due to single transposition of plasmid blaCTX-M to chromosome. In case of isolate N0057, blaCTX-M-15 transposition unit was transferred from plasmid into two different chromosomal regions. In addition, "recurrent" transposition of already existed chromosomally-located blaCTX-M-14 to other chromosomal region was observed in isolates N0211, N0214, N01127, N1682, and N1753; consequently, these isolates possessed two copies of chromosomally-located blaCTX-M-14.

CONCLUSION:
Considering that the isolates (N0211, N0214, N01127, N1682, and N1753) in which the "recurrent "transposition occurred were genetically related on PFGE analysis, our data suggest possibility of accumulation of blaCTX-M on chromosome in CTX-M type ESBL-producing E. coli.

https://www.ncbi.nlm.nih.gov/pubmed/30445208