Resistance Patterns and Prevalence of the Aminoglycoside Modifying Enzymes in Clinical Isolates of Gram Negative Pathogens

In this nationwide study we investigated the occurrence of aminoglycoside resistance patterns and prevalence of the aminoglycoside modifying enzymes (AMEs), aac(6), ant(2) and aph(3), in clinical isolates of Acinetobacter species, E. coli, Klebsiella species and Pseudomonas species isolates from various clinical specimens. A total of 319 clinical specimens recovered from urine, blood, wound, catheter tips and sputum were collected and were processed for identification of bacterial isolates in these specimens. The selected bacterial isolates were examined for susceptibility to Potentox, cefepime, amikacin, tobramycin, meropenem, gentamicin, piperacillin plus tazobactam by disc diffusion method. AMEs were detected by polymerase chain reaction (PCR). A total of 255 Gram negative clinical isolates were recovered from clinical specimens that include 9.0 % of Acinetobacter species, 34.9% of Escherichia coli, 29.0% of Pseudomonas species and 27.0% of Klebsiella species. Among the 255 clinical isolates, 75.7% isolates were found to carry AMEs. The AMEs genes found were aac(6) (43.5 to 51.7%), ant(2) (17.4 to 20.2%) and aph(3) (5.6 to 10.1%) of the isolates. The most prevalent AMEs was aac(6). Our data displayed that Potentox was the most active antibacterial agent against AMEs followed by meropenem. Potentox exhibited more than 93% susceptibility to all 3 types of AMEs (aac, ant & aph) whereas meropenem response was almost 20% lesser with susceptibility ranging not more than 73.4%. Piperacillin plus tazobactam was found to be the least active with less than 20% susceptibility. The susceptibility of other antibacterial agents varied between 20% to <40% %. In conclusion 75.7 % isolates carried AMEs that included aac(6), ant(2) and aph(3) which are responsible for resistance. Among the tested drugs, traditionally used aminoglycoside showed the maximum resistance. Surprizingly, broad spectrum antibiotics like meropenem, cefepime and piperacillin tazobactam also exhibited resistance to aminoglycoside modifying enzyme producing strains. However, in this study, Potentox showed excellent in vitro antibacterial activity up to 95 % of all isolates. We suggest that that Potentox which has been introduced recently into clinical settings would allow clinicinas to overcome the aminoglycoside resistance acquired by some bacterial strains.