Bioactivity of Azolla aqueous and organic extracts against bacteria and fungi

Previous reports indicate the use of the aquatic fern Azolla as medicinal plant in New Zealand and Tanzania against sore throat and cough, respectively. Therefore, the aims were to evaluate the bioactivity of Azolla organic and aqueous extracts against bacteria and yeasts. Organic (dichloromethane:methanol) and aqueous extracts obtained from six Azolla species were tested against bacterial pathogenic and non-pathogenic strains (four Gram-positive and three Gram-negative) and pathogenic fungi (three clinical isolates of Candida albicans and one of C. glabrata), using the agar diffusion method and the broth microdilution assay. The results showed that organic extracts of A. caroliniana and A. rubra and of A. filiculoides inhibited the growth of B. subtilis ATCC 6633 whereas those of A. caroliniana and A. microphylla inhibited the growth of S. aureus ATCC 25923. The MICs were higher than 4 mg/ml for A. caroliniana, A. microphylla and A. rubra and higher than 3.25 mg/ml for A. filiculoides. Aqueous extracts of A. filiculoides, A. caroliniana, A. microphylla, A. rubra and A. pinnata var. pinnata induce a small inhibition zone (1 mm) in C. albicans ATCC 10231 with a MIC higher than 12.5 mg/ml. In conclusion, organic and aqueous extracts of some Azolla species show potential for use against infections caused by Gram-positive bacteria and C. albicans, respectively.