New aminoglycoside-modifying enzymes APH(3')-VIII and APH(3')-IX in Acinetobacter rudis and Acinetobacter gerneri

Analysis of whole-genome sequences of 133 strains of Acinetobacter detected two genes for new types of aminoglycoside 3'-O-phosphotransferase [APH(3')], type VIII in Acinetobacter rudis and IX in A. gerneri. The enzymes were related to each other (49% identity) and to APH(3')-VI (61% and 51% identity, respectively), which is intrinsic to A. guillouiae. The cloned genes conferred kanamycin and amikacin resistance to Escherichia coli but were cryptic or expressed at low levels in the original hosts. The chromosomal location of both genes and the genetic events for acquisition of an ancestral aphA gene by A. rudis and A. gerneri, and loss by A. bereziniae were supported by the molecular phylogenetic tree of these genes. These data confirm that nonpathogenic susceptible bacterial species can be considered as potential reservoirs of resistance genes.