Loss of U1498 methylation in 16S rRNA by
RsmE methyltransferase associates its role with aminoglycoside resistance in mycobacteria.
J Glob Antimicrob Resist 2020;
23:359-369. [PMID:
33186785 DOI:
10.1016/j.jgar.2020.10.006]
[Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Revised: 05/28/2020] [Accepted: 10/06/2020] [Indexed: 11/23/2022] Open
Abstract
OBJECTIVES
Modulation of methylation pattern through mutations in ribosomal methyltransferases is a key mechanism of bacterial drug resistance. However, RsmG (GidB), which specifically methylates G527 in 16S rRNA, remains the only conserved methyltransferase known to be associated with low-level drug resistance in mycobacterial isolates. The mycobacterial RsmE homologue methylates U1498 in 16S rRNA in a highly specific manner. U1498 lies in the vicinity of the binding site for various aminoglycosides in the ribosome. However, the association of methylation at U1498 with altered drug response remains poorly understood.
METHODS
A deletion mutant of the RsmE homologue in Mycobacterium smegmatis was generated by a suicidal vector strategy and drug susceptibility assays were performed on wild-type, knockout and complemented strains with varying concentrations of ribosomal- and non-ribosomal-targeting drugs.
RESULTS
Deletion of the RsmE homologue of M. smegmatis led to an at least two-fold increase in the minimum inhibitory concentrations (MICs) of aminoglycosides that bind in the decoding centre proximal to U1498 in the 30S subunit. The change in MICs was highly specific and reproducible and did not show any cross-resistance to other drug classes. Surprisingly, Rv2372c, the RsmE homologue of Mycobacterium tuberculosis, has the largest number of mutations among conserved ribosomal methyltransferases, after gidB, highlighting the role of mutations in RsmE methyltransferase as a key emerging mechanism of resistance in clinical strains.
CONCLUSION
We present the first evidence of an association of methylation of U1498 in 16S rRNA with development of low-level resistance in mycobacteria that must be tackled in a timely manner.
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