Phenotypic Detection of Efflux Mechanism in Panaminoglycoside Resistant Acinetobacter baumannii from Egyptian Clinical Isolates

Over the last several years, Acinetobacter has emerged as a leading cause of hospital-acquired infections. Aminoglycosides are frequently used in the treatment of invasive infections. Factors associated with the resistance to aminoglycosides include the reduction of drug uptake, modification of aminoglycosides, and aminoglycoside efflux. The aim of our study was to phenotypically detect the presence of efflux mechanism using carbonyl cyanide 3-chlorophenylhydrazone (CCCP) in aminoglycoside resistant Acinetobacter baumannii strains isolated from different hospital wards. In total, 57 A. baumannii isolates were collected from two Egyptian hospitals. The antimicrobial susceptibility pattern was determined. The activity of the efflux system was evaluated using CCCP. Among 57 A. baumannii isolates, most resistance was observed against tobramycin, amikacin, kanamycin, neomycin, and gentamicin. The minimum inhibitory concentrations (MIC) range of A. baumannii was between 2 and 1024 µg/mL based on the tested antibiotics. The phenotypic detection of efflux pumps displaying a reduction of at least two folds in the MICs of antibiotics after addition of the efflux pump inhibitor showed that 19.4% of the isolates became less resistant to kanamycin, 44% to tobramycin, and 46% to amikacin but lower rates were recorded against gentamicin (12.2%) and neomycin (9.4 %). Our study suggests that the efflux mechanism is getting widespread in clinical settings to play an important role in aminoglycoside resistance. Acinetobacter baumannii has the ability to gain resistance to different antibiotic classes through these active efflux pumps. Hence, the application of strict infection control measures together with novel approaches to eradicate those efflux transporters should be applied in hospital settings.