Detection of broad-spectrum aminoglycoside antibiotics through fluorescence-labeling aminoglycoside acetyltransferase(6′)-Ii

Aminoglycosides are among the most commonly used antibiotics. The intensive use of aminoglycoside antibiotics has led to the problem of food contamination and the development of antibiotic-resistant bacteria. In the present study, we developed an effective method for easy sensitive detection of broad-spectrum aminoglycoside antibiotics. Aminoglycoside 6′-N-acetyltransferase family catalyzes the transfer of an acetyl group from acetyl coenzyme A (acetyl-CoA) to the 6′ amino group of the aminoglycoside, which is one of the most widespread determinants of aminoglycoside resistance. Because acetyl-CoA is naturally present only in living organisms, it is expected that the enzyme can bind with aminoglycoside antibiotics without catalysis in vitro. The enzyme was mutated for the introduction of a cysteine residue to flexible loops close to the binding site, which was then labeled with thio-labeling reagent fluorescein-5-maleimide. The labeled enzymes were characterized with kinetic and binding studies of various known aminoglycoside antibiotics. The binding of the labeled enzyme with aminoglycoside antibiotics causes a conformational change of the enzyme, which subsequently changes the hydrophobicity and hydrophilicity environment of fluorescent labeling reagent resulting in emission of fluorescence. This study provides a sensitive detection method for residual aminoglycoside antibiotics and strategies to screen and discover new effective aminoglycoside antibiotics.