Bioactivity of Rhizospheric Acinetobacter baumannii Siderophore Combined with Antibiotics Against Lower Respiratory Tract Pathogenic Bacteria

Abstract

The study focused on extracting and purifying siderophore produced by Acinetobacter baumannii isolated from rhizospheric soil in Baghdad city and evaluating its bioactivity both independently and in combination with selected antibiotics. Bacterial identification was performed using CHROM agar, biochemical, and physiological tests, with confirmation via PCR amplification of the 16S rDNA housekeeping gene. The siderophore was extracted using ethyl acetate after culturing the bacteria in succinate broth and was purified through HPLC, detected at a wavelength of 403 nm. A total of 38 bacterial isolates were obtained from lower respiratory tract infections, including Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Acinetobacter baumannii, Staphylococcus aureus, and Serratia marcescens. Antibiotic susceptibility testing with 13 antibiotics showed the highest resistance rates to ampicillin (65.7%) and ceftriaxone (63.1%), while the lowest resistance was observed with amikacin (15.7%). The synergistic activity of the siderophore combined with sub-MIC concentrations of ceftriaxone, ceftazidime, and gentamycin was tested against multidrug-resistant (MDR) isolates. The most significant antibacterial activity was observed with the combination of siderophore and gentamycin against S. aureus, whereas a minimal effect was noted on A. baumannii. In conclusion, 38 bacterial isolates were successfully identified from lower respiratory tract infections. The combination of siderophore with gentamycin exhibited notable antibacterial activity against S. aureus but was ineffective against A. baumannii.

Keywords

• antibacterial activity, siderophore, acinetobacter baumannii, respiratory tract bacteria