PROSPECTING FOR ANTIMICROBIAL PEPTIDES FROM ANTS: IN VITRO SCREENING AND CHEMICAL CHARACTERIZATION OF ANT EXTRACTS FOR ANTIMICROBIAL ACTIVITY
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Date
2009-07-10
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University of Agricultural Sciences GKVK, Bangalore
Abstract
Insects possess a strong innate defense mechanism that has enabled them conquer
microbially challenging environments and resources. Insects, particularly the immature
stages, are able to survive habitats such as dung, animal carcass and detritus primarily due to
their humoral defense mechanism which guards them against invasive microbes. The insect
humoral factors, identified as primarily comprising antimicrobial peptides effectively tackle
pathogenic infections by microbes. In recent years these antimicrobial peptides (AMPs) have
attracted global attention as potential candidates for therapeutic applications in animal and
human health and agriculture. This has led to a flurry of research on insects to identify
candidate AMPs. Among the insects screened for AMPs, the ants (Hymenoptera:
Formicidae) are known to possess potent antimicrobial peptides which are small linear
peptides.
An exploratory study was taken up to screen for antimicrobial peptides from ants of
peninsular India. Twelve species of ants from three subfamilies viz., Ponerinae, Formicinae
and Myrmicinae were collected for in vitro antimicrobial activity of the whole body extract
of ants in the acidified methanol using the Kirby-Bauer disc diffusion method against three
test microorganisms viz., Escherichia coli, Staphylococcus aureus and Candida albicans. A
strong antimicrobial activity was observed in all the extracts against E. coli than the other two
test microorganisms. The antimicrobial activity of the extract of Oecophylla smaragdina was
found to be stable at temperature as high as 1000C. The extract of O. smaragdina was
however was found to be sensitive to change in the pH. The extract lost the antimicrobial
activity at pH 5.0 and pH 7.0 against the E. coli and C. albicans, but retained its activity
against S. aureus through the range of the pH conditions from 5.0 to 7.0. The micro-
Bradford assay was carried out to confirm the presence of peptides in the extract and had
fairly high concentration of 12. 48µg / ml of extract. The results suggest that the ants are a
good source of antimicrobial compounds, most certainly the peptides, which are heat stable
and active at slightly acidic pH. The study also suggests that antimicrobial activity of the
extracts is restricted to bacteria and has limited activity against fungi.
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