Background: Insects are able to recognize many pathogenic microorganisms and defend against them due to their long evolutionary history. Due to the development of resistance to synthetic antibiotics, researchers are trying to apply insect immune-derived products.

Objectives: The current study aimed to investigate the antibacterial effect of the American cockroach (Periplaneta americana) hemolymph on susceptible and resistant strains of nosocomial bacteria.

Materials and Methods: To stimulate adult cockroaches' immune system, Escherichia coli cells were injected. The antimicrobial effect of the extracted induced and non-induced hemolymph was assayed on many susceptible and resistant pathogenic bacteria.

Results: The comparison of antimicrobial effects of the induced and non-induced hemolymph strains showed that about 43% of bacteria were sensitive to induced hemolymph (P< 0.001), whereas non-induced hemolymph showed no inhibitory effect on the bacteria. Also, evaluation of induced hemolymph effect on the types of strains showed that induced hemolymph affected about 75% of the susceptible bacterial strains (P< 0.001); whereas, it did not affect the resistant strains. Among the tested bacteria, ceftazidime-sensitive E. coli and methicillin-sensitive Staphylococcus aureus showed sensitivity to the induced hemolymph (P< 0.001).

Conclusions: The study results showed that stimulation of the American cockroach’s immunity system lead to production of antibacterial proteins and peptides which had inhibitory effect on the bacteria, depending on the bacterial strains and their sensitivity. Likely this feature of insects can be used as therapeutic strategies to produce natural antimicrobial compounds against the pathogenic bacteria.