Enzyme Mediated Gentamicin Resistance Among Gram-Negative Clinical Isolates

Abstract

Gentamicin is a broad-spectrum, bactericidal antibiotic of the aminoglycoside family. It has been shown through extensive evaluation to be effective in the treatment of serious gram- negative bacillary infections (1-5). Gentamicin is one of the few antimicrobial agents available for the treatment of life- threatening infections due to Pseudomonas aeruginosa (114-116), an organism of increasing etiological significance in opportunistic infections (6). | Perhaps as a result of the use of gentamicin, and its significant misuse, the incidence of resistance to gentamicin among clinical isolates (of formerly susceptible bacteria) is on the rise (7-12). Resistance to the aminoglycosides is believed to be due to three basic mechanisms (13,14), The best characterized mechanism is the enzyme-mediated inactivation of antibiotic activity. To date eight different enzymes have been described (15). The three primary classes of enzymes (based upon the nature of the group they transfer to the aminoglycoside molecule) are: (a) an adenylylating enzyme (adenylyltrans-ferase) (13), (b) an acetylating enzyme (acetyltransferase) (13), and (c) a phosphorylating enzyme (phosphotransferase) (13).