Komeda Tomoki, Hishinuma Tomomi, Kirikae Teruo, Tada Tatsuya
Department of Microbiology, Juntendo University School and Graduate School of Medicine, Bunkyo-ku, Tokyo, Japan.
Juntendo Advanced Research Institute for Health Science, Bunkyo-ku, Tokyo, Japan.
J Infect Chemother. 2025 Feb;31(2):102536. doi: 10.1016/j.jiac.2024.10.004. Epub 2024 Oct 5.
The mechanism of aminoglycoside resistance due to abnormal hemin synthesis remains unclear. We investigate an Escherichia coli strain with a single amino acid substitution at position 85 of HemC.
An aminoglycoside-resistant Escherichia coli DH5α was selected by passaging in Lysogeny Broth (LB) medium containing amikacin. Whole genome sequencing was performed to determine the genetic profile of the strain. An isogenic strain of E. coli DH5α was created. Growth rates, drug susceptibilities and expressions of the heme synthetic genes were compared between the original strain and the isogenic strain.
Whole genome sequencing revealed a nucleotide substitution at position 254 of hemC from adenine (A) to thymine (T), resulting in an amino acid substitution at position 85 of HemC from histidine (H) to leucine (L). There were no mutations in other heme synthetic genes, including hemA, hemB, hemC, hemD, hemE, hemF, hemG, hemH, hemL, hemN, hemX and hemY. The isogenic strain of E. coli DH5α with H85L in HemC was less susceptible to aminoglycosides, and its growth was slower than that of E. coli DH5α before passage. Quantitative real-time PCR showed that the expression of hemA was higher and the expressions of hemL, hemG and hemX lower in the isogenic strain than before passage.
This is the first report of aminoglycoside resistance due to an amino acid substitution in HemC. These findings suggested that mutations in the heme synthetic genes may indirectly affect the growth rates of E. coli strains and their susceptibilities to aminoglycosides.
由于血红素合成异常导致氨基糖苷类耐药的机制尚不清楚。我们研究了一株在HemC第85位有单个氨基酸取代的大肠杆菌菌株。
通过在含有阿米卡星的溶原肉汤（LB）培养基中传代筛选出一株耐氨基糖苷类的大肠杆菌DH5α。进行全基因组测序以确定该菌株的基因图谱。构建了大肠杆菌DH5α的同基因菌株。比较了原始菌株和同基因菌株之间的生长速率、药敏性及血红素合成基因的表达。
全基因组测序显示hemC第254位核苷酸由腺嘌呤（A）替换为胸腺嘧啶（T），导致HemC第85位氨基酸由组氨酸（H）替换为亮氨酸（L）。其他血红素合成基因，包括hemA、hemB、hemC、hemD、hemE、hemF、hemG、hemH、hemL、hemN、hemX和hemY均无突变。HemC中具有H85L的大肠杆菌DH5α同基因菌株对氨基糖苷类药物的敏感性较低，其生长速度比传代前的大肠杆菌DH5α慢。定量实时PCR显示，同基因菌株中hemA的表达高于传代前，而hemL、hemG和hemX的表达低于传代前。
这是关于HemC中氨基酸取代导致氨基糖苷类耐药的首次报道。这些发现表明，血红素合成基因的突变可能间接影响大肠杆菌菌株的生长速率及其对氨基糖苷类药物的敏感性。
