Characterization of a novel aminoglycoside resistance gene, aadA34, identified from Serratia ureilytica S24.

Bacterial resistance to aminoglycoside drugs is becoming increasingly severe due to their widespread use in agriculture and human medicine. Based on the whole-genome sequencing and molecular methods, a novel aminoglycoside resistance gene designated aadA34 was identified from a multiple-drug-resistant bacterium Serratia ureilytica S24, which was isolated from sewage at a poultry farm. The aadA34 gene conferred resistance to spectinomycin and streptomycin, with MIC levels increased by 64- and 128-fold, respectively, for spectinomycin and streptomycin compared with the control strain (pUCP20/E. coli DH5α). The amino acid (aa) sequence of AadA34 was found to share the highest identity (60.09%) with the function-characterized aminoglycoside nucleotidyltransferase AadA16. Corresponding to the MIC results of the aadA34 gene, the enzyme AadA34 exhibited high affinity and catalytic efficiency against spectinomycin or streptomycin. Approximately 160 aa longer than other functionally characterized AadA proteins, the aadA34 gene was found to be generally encoded in bacteria of the genus Serratia, especially in the species S. ureilytica and S. marcescens, which were isolated from various sources including some of clinical significance.