Biological effectivenes of Ligaria cuneifolia and Jodina rhombifolia extracts against phytopathogenic bacteria: microbiological and toxicological tests

SOBERON, J. R.; DIP, M.; SGARIGLIA, M. A.; SAMPIETRO, D.A.; VATTUONE, M.A.

Tucumán

Congreso; VII Congreso Argentino de Microbiología General; 2011

Sociedad Argentina de Microbiología General

Introduction: phytopathogenic bacteria are one of the most serious hazards faced by plants, resulting in major economic losses worldwide. The main genera implicated are: Agrobacterium, Erwinia, Pseudomonas and Xanthomonas. These strains, under favorable environmental conditions cause devastating diseases. One promising alternative is the use of plants employed in folk medicine to obtain chemical agents with high antimicrobial activities and low toxicity. Ligaria cuneifolia y Jodina rhombifolia are argentinean northwestern species used in folk medicine with several purposes, that may be sources of those kind of compounds. Materials and Methods: Bacterial strains: [phytopathogenic] Xanthomonas campestris, Agrobacterium tumefaciens, Pseudomonas corrugata, Pseudomonas syringae and Erwinia carotovora, [non phytopathogenic] Escherichia coli and Staphylococcus aureus (reference strains). Plant extracts: dichloromethane, methanol and aqueous extracts were prepared from the plant material dried powdered. Antimicrobial activity tests: Agar dilution (macrodilut ion) and broth dilution (microdilution) assays were employed to atta in Minimum Inhibitory Concentrations (MICs) and Minimum Bactericidal Concentrations (MBCs). Oxytetracycline and Sptreptomycine were used as reference drugs. General to xicity: Artemia salina larvae lethality test (Sober6n et al., 2007) was employed to attain the Lethal Concentrations 50 (LC50s). Results and discussion: L. cuneifolia extracts generated high er yields of extracted material (EM) and high er content of phenolic compounds (37.8 mg/mL) than J. rhombifolia extracts. L. cuneifolia methanolic extract showed inhibitory effects on all assayed strains, at concentrations below 0.16 mg EM/mL. This extract exhibited bactericidal effect on five of the seven strains, with MBCs ranged from 0.078 to 0.312 mg/mL. The infusion had inh ibitory activity on the strains at concentrations above 5 mg ME/mL. J. rhombifolia extracts showed no significant antibacterial activ ity on t he assayed strains, as nor dichloromethane extract presented any inhibitory effect. The more active antibac teria l extracts were also the more toxic on A. salina, but the concentration required to exert antibacterial activities were sign if icantly lower than LC50s, because LC50s and MICs rat ios were near 70, i.e. the concentrations required to inhibit bacterial growth wer e 70 t imes lower than toxic concentrations. According to the results we conclude that L. cuneifolia synthesizes active metabolites against the assayed strains at low toxic concentrations.