Cloning of AAC(3) and AAD(2″) genes from Acinetobacter : differential expression in the host strain

The mechanism of resistance to gentamicin and tobramycin in a clinical isolate of Acinetobacter baumannii , in which aminoglycoside-modifying enzymes were not detected, was investigated. To determine whether both genes are expressed in the host Acinetobacter strain, we extracted total cellular RNA from this stain, and Northern blots were hybridized with the clones AAC(3) and AAD(2") structural genes. mRNA transcribed from the AAC(3) gene alone was detected. This shows that cloning a functional resistance gene is not sufficient in itself to investigate mechanisms of resistance in bacterial strains without detectable aminoglycoside-modifying activity.