A Novel Amino Acid Deletion and Substitution inamrBGene Associated with Gentamicin Susceptibility inBurkholderia pseudomalleifrom Malaysian Borneo

Abstract

Burkholderia pseudomalleiis a highly pathogenic saprophyte that is intrinsically resistant to a wide variety of antibiotics. Resistance to gentamicin is considered as an earmark ofB. pseudomallei. However, rare susceptible strains have been isolated in certain regions due to gene mutations. Currently, data on the susceptible strains’ prevalence and the actual causal mutations are still scarce, particularly in Malaysian Borneo. A pool ofB. pseudomalleiisolates (n= 46) were screened for gentamicin susceptibility and phenotypically confirmed using the gradient minimal inhibitory concentration method. Three isolates were gentamicin-susceptible strains and were identified as having originated from Bintulu, Sarawak, Malaysian Borneo. TheamrBgene mutation in these mutant strains was analysed, and the effect of amino acid substitution on the stability of the amrB protein was determined by usingin silicoanalysis. The mutagenesis analysis identified a polymorphism-associated mutation, g.1056T>G, and two susceptible-associated mutations identified as novel in-frame amino acid deletion p.Val412del and amino acid substitution p.Thr368Arg that compromised gentamicin resistance.In silicoanalysis using amrB homology-modelled and AlphaFold-solved structures proposed the role of p.Thr368Arg amino acid substitution in conferring GEN susceptibility by other mechanisms than destabilising the structure of amrB protein, which is most probably due to the mutation’s location in the highly conserved region. The findings have shed light on the phenotypic characteristics and mutations involved in theamrBgene of thegentamicin-susceptibleB. pseudomallei.