Disease relevance of aadD

• Examination of two conjugative plasmids from strains of Staphylococcus aureus isolated in North America indicated that the aadD determinant on these plasmids is located on an integrated copy of pUB110 [1].
• The naturally occurring plasmid pSTS7 from Staphylococcus epidermidis mediated resistance to tetracycline via a tetL gene and to kanamycin and neomycin via an aadD gene [2].

High impact information on aadD

• The mec region was found to harbor an insert of the transposon Tn554, which encodes spectinomycin and macrolide-lincosamide-streptogramin B resistance, and a 4.6-kb segment of DNA that contains the kanamycin resistance gene aadD [3].
• The aadD gene, encoding tobramycin resistance, failed to be amplified in all cases, indicating absence of the gene or the entire plasmid pUB110 from the mec DNA [4].
• In staphylococci, linked resistance to the aminoglycosides kanamycin, neomycin, paromomycin, and tobramycin (KmNmPmTmr) is generally mediated by an aadD determinant which encodes production of an adenyltransferase aminoglycoside modifying enzyme, AAD(4',4'') [1].
• The aadD resistance determinant is located on small multicopy plasmids such as pUB110, and has also been found on large multiresistance plasmids and on the chromosome in some strains [1].
• Analysis of the nucleotide sequence and restriction map revealed a complete homology of the blmS-containing region of the integrate to wild type pSK41, except for the deletion of aadD and a part of the repU gene [5].

Associations of aadD with chemical compounds

• Regarding aminoglycoside-modifying enzymes, 7 strains (12%) appeared to be producing aminoglycoside 4',4"-adenyltransferase AAD(4',4") encoded by aadD without coproduction of bifunctional aminoglycoside 6'-acetyltransferase/2"-phosphotransferase AAC(6')/APH(2") encoded by aacA-aphD (referred to as tobramycin-resistant type, TOBr) [6].
• AAD(4',4"), encoded by aadD which was reported to be closely linked with bleomycin (BLM)-resistance determinant, could be seen in 100% MRSA strains and ca. 90% strains expressed AAC(6')/APH(2") [6].

References