Antimicrobial susceptibility of non-fermenting Gram-negative isolates to isepamicin in a region with high antibiotic resistance

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The alarmingly increasing resistance rates among non-fermenting Gram-negative species, particularly Pseudomonas aeruginosa and Acinetobacter baumannii, intensified the interest in alternative antibiotic treatment options. Isepamicin, an old aminoglycoside, may play a role in the treatment of patients with infections caused by those multi-drug resistant pathogens. We evaluated the antimicrobial activity of isepamicin against non-fermenting Gram-negative isolates collected of the microbiological laboratory at the University Hospital of Heraklion, Crete, Greece from 2004 to the first trimester of 2011. We tested a total of 4,219 isolates (66.2% Pseudomonas spp., 30% Acinetobacter spp., 3.8% other non-fermenters). The lower respiratory tract, pus, and urine were the most frequent sites of isolation (29.7%, 19.9%, and 12.9%, respectively). Overall, 2768 (65.6%) of the evaluated isolates were susceptible to isepamicin (including 79.9 % of Pseudomonas spp, 37.2 % of Acinetobacter spp, 43.1 % of other non-fermenters). Isepamicin exhibited higher antimicrobial activity compared to broad spectrum penicillins, cephalosporins, other aminoglycosides, carbapenems, and fluoroquinolones. Only colistin was more active than isepamicin. Additionally, 41.7% of carbapenem-resistant and 53.2% of colistin-resistant P. aeruginosa isolates were susceptible to isepamicin. The susceptibility rates for the respective types of A. baumannii isolates were 12% and 6.2%. Yet, isepamicin was active against 29.2% of A. baumannii that were resistant to all other tested aminoglycosides. Isepamicin exhibits considerable antimicrobial activity against Gram-negative non-fermenters in a region with high antimicrobial resistance. Particularly, isepamicin may provide a therapeutic option for infections from carbapenem- and colistin-resistant P. aeruginosa and other aminoglycoside-resistant A. baumannii. Further modifications in the aminoglycoside molecule may provide formulations with enhanced antimicrobial activity.