The pygidial gland secretion of the forest caterpillar hunter, Calosoma (Calosoma) sycophanta: the antimicrobial properties against human pathogens

Recently, various insect secretions have been tested as possible antimicrobial agents. In beetles, these secretions are essentially products of various exocrine glands, of which particular emphasis is on pygidial glands that are common for the suborder Adephaga. The antimicrobial potential of the pygidial gland secretion isolated from the adults of Calosoma sycophanta against human pathogens has been tested and compared with the potential of other carabid species, particularly within the tribe Carabini. The antimicrobial assay includes a microdilution method which was applied in order to determine the minimal inhibitory, minimal fungicidal and minimal bactericidal concentrations. It has been tested the effect of the secretion against eight strains of fungal and eight strains of bacterial species. The secretion sample of the tested carabid species has shown statistically significant antifungal effect against all strains of treated micromycetes, the highest in comparison with previously tested carabids (Carabus spp., Laemostenus punctatus and Abax parallelepipedus). Aspergillus versicolor proved to be the most sensitive micromycete, while the remaining seven fungal strains have shown the same level of sensibility. In comparison with commercial mycotics ketoconazole and bifonazole, applied as positive controls, the tested secretion showed much higher antifungal activity for all fungal strains. Antibacterial effect has been manifested only against one bacterial strain (Escherichia coli), contrary to other previously studied carabid species. These observations might have a significant impact on the ecological domain and possible purpose in biomedical studies and applications in the future. Additionally, morpho-histology of the pygidial glands of C. sycophanta is investigated and discussed.