Spectrum of Aminoglycoside Modifying Enzymes in Gram-Negative Bacteria Causing Human Infections.

 Aminoglycosides are formidable broad-spectrum antibiotics used in clinical settings; woefully their usage has been reduced by the emergence and distribution of resistance mainly due to aminoglycoside modifying enzymes (AME).  This study was performed to determine the diverse prevalence of AME and their pattern of occurrence in the clinical isolates of gram-negative bacteria. This study also aimed to detect the presence of AMEs that are prevalent in gram-positive bacteria, among gram negatives.  A total number of 386 clinical isolates were included in this study. Polymerase chain reaction revealed the prevalence rate of AMEs screened [aac(6')-lb, aac(3')-I, aac(3')-II, aac(3')-VI, ant(2')-I, ant(4')-IIb, aac(3')-III, aac(3')-IV, aph(2')-Ib, aph(2')-Ic, aph(2')-Id, aac (6')-Ie- aph(2')-Ia, and aph(3')-IIIa]. Conjugation experiment was performed for the clinical isolates which harbored any one of the AME which was prevalent in gram-positive bacteria [aph(3')-IIIa, aac(6')-Ie-aph(2')-Ia].  aac(6')-lb is the most prevalent AME, followed by aac(3')-I, aph(3')-VI, aac(3')-VI, and aac(3')-II. The AMEs such as ant (2')-I, ant(4')-IIb, aac(3')-III, aac(3')-IV, aph(2')-Ib, aph(2')-Ic, and aph(2')-Id were not established in our study isolates. The rate of prevalence of aph(3')-IIIa, aac(6')-Ie-aph(2')-Ia-the AMEs encountered in gram-positive and their co-existence was 19.68% and the conjugation experiment revealed their transfer via plasmids.  This is the first report from India revealing the presence and prevalence of AMEs which are often encountered among gram-positive bacteria in gram negatives and their presence on conjugative plasmids.