Evaluation of Resistance of Phytopathogenic Bacteria to Agricultural Antibiotics

Abstract

Agricultural antibiotics are widely used to inhibit the growth of phytopathogenic bacteria involved in plant diseases. However, continuous antibiotic overuse in crop production may lead to the development of antibiotic resistance in phytopathogenic bacteria. This study was conducted to evaluate the resistance to three different agricultural antibiotics (oxytetracycline+streptomycin, streptomycin, and validamycin A) in 91 strains of phytopathogenic bacteria including <i>Pectobacterium carotovorum</i>, <i>Pseudomonas syringae</i> pv. <i>actinidiae</i>, <i>Clavibacter michiganensis</i> subsp. <i>michiganensis</i>, <i>C. michiganensis</i> subsp. <i>capsici</i>, and <i>Xanthomonas arboricola</i> pv. <i>pruni</i>. Bacterial growth in the presence of various concentrations of validamycin A was also assessed spectrophotometrically by analyzing the optical density. All strains did not grow when the cells were exposed to oxytetracycline+streptomycin or 100× of streptomycin. However, among the 91 strains, 4% and 2% strains showed bacterial growth at the concentrations of 1× and 10× of streptomycin, respectively. Furthermore, 97%, 93%, and 73% strains were resistant to the 1×, 10×, and 100× of validamycin A, respectively, and especially, <i>P. carotovorum</i> contained the highest resistance to the validamycin A. Minimum bactericidal concentration values of validamycin A did not correlate with the patterns of agricultural antibiotic resistance. Further studies are needed to understand the incidence and development of antibiotic resistance in phytopathogenic bacteria.