Prevalence of Aminoglycoside Resistance Genes in Acinetobacter baumannii Isolates

Acinetobacter baumannii is one of the major causes of nosocomial infections and is resistant to most available antibiotics. Aminoglycosides remain as drugs of choice for treatment of Acinetobacter infections yet resistance to aminoglycosides has increased in the recent years.

The present study investigated the prevalence of genes encoding aminoglycoside-modifying enzymes in A. baumannii strains isolated from patients of Tabriz city, northwest of Iran.

A total of 103 Acinetobacter isolates were collected from Imam Reza Hospital of Tabriz University of medical sciences. Antimicrobial susceptibility patterns of the isolates to different antimicrobial agents including cephalosporins, gentamicin, amikacin, tobramycin, colistin and polymyxin, were evaluated by the disc diffusion method. The frequency of aminoglycoside modifying enzymes encoding genes aacC1, aphA6, aadA1 and aadB was analyzed by the PCR method.

Antimicrobial susceptibility analysis showed that the highest resistance was towards beta-lactam antibiotics including cephalosporins whereas the highest sensitivity was observed towards colistin (77%) and polymyxin (84%). The resistance rate to aminoglycosides was 81%, 86% and 63% for amikacin, gentamicin and tobramycin, respectively. The PCR results showed that among the 103 A. baumannii isolates, 56 (65.11 %) were positive for aacC1, 52 (60.46 %) for aphA6, 24 (27.9 %) for aadA1 and 16 (18.6 %) for aadB resistant genes.

The results of this study indicated that the genes encoding aminoglycoside-modifying enzymes are prevalent in A. baumannii isolates in the study region, which highlighted the necessity of considering preventive measures to control dissemination of these resistance genes.