Flavonoids as Antimicrobials Against Streptomyces scabies: a Causative Agent of Common Scab in Potatoes
Common scab disease (CS), caused by Streptomyces scabies, is an economically important disease of potatoes characterized by lesion and scab formation on the surface of potato tubers, resulting in large economic losses globally. The lack of effective treatments against this disease accounts for its global spread and negative impact. Recently, plant extracts were shown to effectively inhibit the growth of S. scabies in culture. To identify the antimicrobial agent in plant extracts, S. scabies was grown in the presence of a selected library of 20 flavonoids. The flavonoids that showed the greatest inhibition of S. scabies growth were sophoraflavanone G (SG), jaceosidin, baicalein, and quercetin. Minimum inhibitory concentrations (MICs) for the effective flavonoids were calculated to be 6.8 ± 0.4 μM, 100.0 ± 2.1 μM, 202.9 ± 5.3 μM and 285.2 ± 6.8 μM, respectively. A live/dead assay showed complete cell death in the presence of SG. SEM imaging showed damaged cell morphologies when S. scabies was exposed to these flavonoids suggesting that these plant compounds act on S. scabies through a bactericidal mechanism.