Abstract: The antimicrobial activities of the methanolic extracts of Euphorbia hirta L
leaves, flowers, stems and roots were evaluated against some medically important bacteria
and yeast using the agar disc diffusion method. Four Gram positive (Staphylococcus
aureus, Micrococcus sp., Bacillus subtilis and Bacillus thuringensis), four Gram negative
(Escherichia coli, Klebsiella pneumonia, Salmonella typhi and P. mirabilis) and one yeast
(Candida albicans) species were screened. Inhibition zones ranged between
16–29 mm. Leaves extract inhibited the growth of all tested microorganisms with large
zones of inhibition, followed by that of flowers, which also inhibited all the bacteria except
C. albicans. The most susceptible microbes to all extracts were S. aureus and Micrococcus
sp. Root extract displayed larger inhibition zones against Gram positive bacteria than Gram
negative bacteria and had larger inhibition zones compared to stem extract. The lowest
MIC values were obtained with E. coli and C. albicans (3.12 mg/mL), followed by S.
aureus (12.50 mg/mL) and P. mirabilis (50.00 mg/mL). All the other bacteria had MIC
values of 100.00 mg/mL. Scanning Electron Microscopic (SEM) studies revealed that the
cells exposed to leaf extract displayed a rough surface with multiple blends and
invaginations which increased with increasing time of treatment, and cells exposed to leaf
OPEN ACCESS
Molecules 2010, 15
6009
extract for 36 h showed the most damage, with abundant surface cracks which may be
related to final cell collapse and loss of function. Time-kill assay of C. albicans indicated a
primarily fungicidal effect at 1- and 2-fold MIC. E. hirta extracts had LC50 values of 0.71,
0.66, 0.41 and 0.03 mg/mL for stems, leaves, roots and flowers, respectively against
Artemia salina. Hence, these plants can be used to discover new bioactive natural products
that may serve as leads in the development of new pharmaceuticals.
Keywords: antimicrobial; Euphoribia hirta; MIC; SEM; time-kill assay;
Artemia salina napulii