Isolation and Purification of an Antibacterial Protein from Immune Induced Haemolymph of American Cockroach, Periplaneta americana

<p><strong>Background: </strong>Antimicrobial peptides<em> </em><em>play a role as effectors substances in the immunity of vertebrate and inverte­brate hosts. In the current study, antimicrobial peptide was isolated from the haemolymph</em><em> </em><em>of the American cock­roach, </em><em><em>Periplaneta americana</em></em><em>.</em><em></em><em><br /></em><strong>Methods:</strong><em><em> Micrococcus luteus</em></em><em> </em><em>as Gram-positive bacteria and </em><em><em>Escherichia coli</em></em><em> as Gram-negative bacteria were candi­date for injection. Induction was done by</em><em> </em><em>injecting both bacteria into the abdominal cavity of two groups of cock­roaches separately. The haemolymphs were collected 24 hours after post injection and initially tested against both bacteria. Subsequently, </em>the immune induced haemolymph was purified by high performance liquid chromatography (HPLC) to separate the proteins responsible for the antibacterial activity.<em></em><em><br /></em><strong>Results:</strong><em> The non-induced haemolymph did not show any activity against both bacteria whereas induced haemo­lymph exhibited high activity against</em> <em><em>M. luteus</em></em><em> </em>but did less against <em>E. </em><em><em>coli</em></em>. Two fractions showed antibacterial activ­ity against <em><em>M. luteus.</em></em><em> </em><em>F</em>inally the molecular weight of the isolated antibacterial proteins were determined as 72 kDa and 62 kDa using SDS-PAGE.<strong><br />Conclusion:</strong> Induced haemolymph of American cockroaches has the ability to produce peptides to combat against <em>Gram-positive bacteria </em>when an immune challenge is mounted. Further work has to be done to sequence of the pro­tein, which it would be advantageous.