INSECTS AS SOURCES OF ANTIMICROBIALS: IN VITRO SCREENING OF EXTRACTS OF DUNG INHABITING INSECTS FOR ANTIMICROBIAL ACTIVITY
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Date
2009-08-25
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University of Agricultural Sciences GKVK, Bangalore
Abstract
Dung beetles which inhibit the microbially challenging environment of the dung
were screened for antimicrobial peptides. The extracts from 16 species were obtained
both from ‘unchallenged’ and ‘challenged’ individuals; each extract was tested against
Eschericia coli, Staphylococcus aureus and Candida albicans.
Protocols were developed for collection and processing of dung beetles for
preparation of extracts to assess antimicrobial activity. The antimicrobial activity against
E. coli was particularly important since the strain of E. coli used in the study was resistant
to all antibiotics, including Methicillin. There were significant differences among the
extracts from different species with respect to antimicrobial activity. The extract from
Copris repertus showed the highest level of antimicrobial activity at 10 h and 20 h after
treatment. The antimicrobial activity of the ‘challenged’ extracts was significantly greater
than the ‘unchallenged’ extracts in bioassay against all the three test microbes. Further,
positive correlation in antimicrobial activity of ‘challenged’ and ‘unchallenged’ extracts
was also observed.
The significant increase in the antimicrobial activity of the challenged extracts is
indicative of the evolution of inducible defenses which respond quickly to produce nonspecific
antimicrobial compounds as the first line of defense against invading pathogens.
The results of the bioassay showed that extracts from all the species were significantly
more active against S. aureus; as reflected by a significant larger zone of inhibition. The
results showed that dung beetles belonging to the guild of ‘breeders’ had a stronger
immune response, in the sense that the extracts from such species showed a high level of
antimicrobial activity at least at 10 h post-treatment as opposed to ‘rollers’ and
‘tunnelers’.
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