Antibacterial activity of south African Helichrysum species

Acetone extracts of Helichrysum callicomum, H. glomeratum, H. hypoleucum, H. odoratissimum, H. piloselium and H. rugulosum were investigated for antibacterial activities against ten bacteria using the agar diffusion method. Epicuticular (shaken) ana homogenized extracts of H. hypoleucum, H odoratissimum and H. rugulosum significantly inhibited the growth of Bacillus cereus, B. pumilus, B. subtilis, Micrococcus kristinae and Staphylococcus aureus (all Gram-positive bacteria) and Enterobacter cloacae (Gram-negative) at a concentration range of 0.01 to 1.0 mg/ml. In addition, the epicuticular extract of H. hypoleucum was active against Escherichia coli and Pseudomonas aeruginosa whereas the homogenized extract only had activity against P. aeruginosa. None of the other six extracts inhibited the growth of E. coli, Klebsiella pneumoniae, P. aeruginosa and Serratia marcescens, all Gram-negative bacteria. The extracts of H. glomeratum and H. pilosellum had no activity against any of the organisms tested. Shaken extracts proved to be more bioactive than homogenized extracts.