Detection of antibiotic resistance genes in culturable bacteria isolated from soils around mines in Hamedan, Iran

Antibiotic resistance genes are considered to be emerging contaminants. Considering the limited number of papers on detection of antibiotic resistance genes in metal-polluted soils of Iran and due to the fact that nonclinical strains carrying resistance determinants can be the origin of resistance genes in clinical isolates, the present study was conducted to detect some resistance genes (i.e., bla TEM , van A, tet B, str A, and aac(3) - II ) in the most prevalent culturable bacteria isolated from soils around mines. A total of 70 species of Pseudomonas , Azotobacter , Enterobacter , and Bacillus were isolated from soils under different land uses. Polymerase chain reaction was used to detect resistance genes in the isolates. The bla TEM gene was the most abundant gene detected in the isolates (45.71%). The number of Azotobacter , Pseudomonas , and Enterobacter isolates containing bla TEM was higher in the agricultural and pasture soils than in the mining waste soils (28.57%, 57.14%, and 20%, respectively), but the pasture and mining waste soils proved to harbor more Bacillus species containing bla TEM compared to the agricultural soils (64.28%, 50%, and 42.86%, respectively). The van A gene was found in 5.71% of all the strains, and only one Pseudomonas isolates harbored aac(3) - II . The tet B and str A genes were not detected in any of the isolates. More than 77% of the isolates were phenotypically resistant to β-lactams, and 28.57%, 40%, and 31.43% of them were resistant to streptomycin, vancomycin, and tetracyclines, respectively. Overall, the high number of bacteria containing at least one resistance gene isolated from the samples indicated the persistence of environmental reservoirs of resistance genes in the metal-polluted soils.