Tehran University of Medical Sciences Journal of Arthropod-Borne Diseases 2322-1984 10 4 2016 10 24 519 527 EN Hamid Reza Basseri Department of Medical Entomology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Amir Dadi-Khoeni Department of Biology, Payame Noor University, Tehran, Iran Ronak Bakhtiari Departmet of Photobiology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Mandan Abolhassani Department of Medical Entomology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran Reza Hajihosseini-Baghdadabadi Department of Biology, Payame Noor University, Tehran, Iran 2015 12 05 2015 12 05 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. https://jad.tums.ac.ir/index.php/jad/article/view/337 https://jad.tums.ac.ir/index.php/jad/article/download/337/293