Identification and Characterization of a Novel Aminoglycoside 3 ''-Nucleotidyltransferase, ANT(3 '')-IId, From Acinetobacter lwoffii

A novel plasmid-encoded aminoglycoside 3"-nucleotidyltransferase ANT(3")-IId, was discovered in Acinetobacter lwoffi strain H7 isolated from a chick on an animal farm in Wenzhou, China. The whole-genome of A. lwoffii H7 consisted of one chromosome and five plasmids (pH7-250, pH7-108, pH7-68, pH7-48, and pH7-11). ant(3")-IId was identified as being encoded on pH7-250, sharing the highest amino acid identity of 50.64% with a function-known resistance gene, ant(3")-IIb (KB849358.1). Susceptibility testing and enzyme kinetic parameter analysis were conducted to determine the function of the aminoglycoside 3"-nucleotidyltransferase. The ant(3")-IId gene conferred resistance to spectinomycin and streptomycin [the minimum inhibitory concentration (MIC) levels of both increased 16-fold compared with the control strain]. Consistent with the MIC data, kinetic analysis revealed a narrow substrate profile including spectinomycin and streptomycin, with K-cat/K-m ratios of 4.99 and 4.45 x 10(3) M-1 S-1, respectively. Sequencing analysis revealed that the ant(3")-IId gene was associated with insertion sequences (IS) element [Delta ISAba14-Delta ISAba14-hp-orf-orf-orf1-ant(3")-IId], and ant(3")-IId were identified in plasmids from various Acinetobacter species. This study of the novel aminoglycoside 3''-nucleotidyltranferase ANT(3")-IId helps us further understand the functional and sequence characteristics of aminoglycoside 3"-nucleotidyltranferases, highlights the risk of resistance gene transfer among Acinetobacter species and suggests that attention should be given to the emergence of new aminoglycoside 3"-nucleotidyltranferase genes.