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

BACKGROUND Antimicrobial peptides 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 of the American cockroach, Periplaneta americana. METHODS Micrococcus luteus as Gram-positive bacteria and Escherichia coli as Gram-negative bacteria were candidate for injection. Induction was done by 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, the immune induced haemolymph was purified by high performance liquid chromatography (HPLC) to separate the proteins responsible for the antibacterial activity. RESULTS The non-induced haemolymph did not show any activity against both bacteria whereas induced haemolymph exhibited high activity against M. luteus but did less against E. coli. Two fractions showed antibacterial activity against M. luteus. Finally the molecular weight of the isolated antibacterial proteins were determined as 72 kDa and 62 kDa using SDS-PAGE. CONCLUSION Induced haemolymph of American cockroaches has the ability to produce peptides to combat against Gram-positive bacteria when an immune challenge is mounted. Further work has to be done to sequence of the protein, which it would be advantageous.