Instability of the 16S rRNA methyltransferase-encoding npmA gene: why have bacterial cells possessing npmA not spread despite their high and broad resistance to aminoglycosides?
2018
The NpmA bacterial 16S rRNA
methyltransferase, which is identified from Escherichia coli strains, confers high resistance to many types of
aminoglycosideupon its host cells. But despite its resistance-conferring ability, only two cases of its isolation from E. coli (14 years apart) have been reported to date. Here, we investigated the effect of the npmA gene on
aminoglycosideresistance in Pseudomonas aeruginosa and Klebsiella pneumoniae and its stability in E. coli cells by comparing it with armA, another 16S rRNA
methyltransferasegene currently spreading globally. As a result, we found that npmA conferred resistance to all types of
aminoglycosideantibiotics we tested (except streptomycin) in both P. aeruginosa and K. pneumoniae, as well in E. coli. In addition, co-expression of armA and npmA resulted in an additive effect for the resistance. However, in return for the resistance, we also observed that the growth rates and the cell survivability of the strains transformed with the npmA-harboring plasmids were inferior than those of the control strains and that these plasmids were easily disrupted by IS10, IS1, and IS5
insertion sequences. We discuss these data in the context of the threat posed by pathogenic strains possessing npmA.
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