Antibiotic sensitivity of phosphate-mobilizing rhizobacteria of wheat rhizosphere

Antibiotic sensitivity is a serious problem, especially relevant when using bacterial biofertilizers. Many strains of rhizobacteria used as bacterial biofertilizers and biofungicides demonstrate resistance to several antibiotics or contain antibiotic resistance genes. In this study, we investigated the antibiotic sensitivity of 12 strains of phosphate-mobilizing rhizobacteria isolated from the rhizosphere of wheat grown on irrigated lands of the Sirdarya, Tashkent andijan and Kashkadarya regions of Uzbekistan in 2021, belonging to the genera Enterobacter, Rahnella, Bacillus, Pantoea and Pseudomonas, to seven antibiotics of different classes: erythromycin, streptomycin, gentamicin, chloramphenicol, amikacin, tetracycline and cephalexin. Most strains showed high sensitivity to aminoglycosides, chloramphenicol and tetracycline, while some strains showed resistance to erythromycin, streptomycin and cephalexin. Moderate resistance to streptomycin, tetracycline and cephalexin was noted, especially among strains of the genus Enterobacter. Strains of the genus Rahnella showed moderate resistance to streptomycin, gentamicin, tetracycline and cephalexin. Strains of the genus Bacillus showed moderate resistance to chloramphenicol, tetracycline and cephalexin; the diameter of the zones of growth inhibition was 15 mm to 17 mm. The strain P. agglomerans 19 showed moderate resistance only to tetracycline, while remaining sensitive to other antibiotics, but this result requires confirmation through molecular genetic studies in the future. The data revealed are important for assessing the safety of phosphate-mobilising rhizobacteria when used as bacterial fertilisers, taking into account their resistance, to minimise the risk of spreading antibiotic resistance genes (ARGs) in agroecosystems.