Escherichia coli with increased aminoglycoside resistance due to an amino acid substitution at position 85 of HemC.

OBJECTIVE

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.

METHODS

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.

RESULTS

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.

CONCLUSION

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.