Abstract
The global spread of multi-resistant pathogens responsible for infections, which cannot be treated with existing drugs such as antibiotics, is of particular concern. Antibiotics are becoming increasingly ineffective and drug resistance is leading to more difficult-to-treat infections; therefore, new bioactive compounds with antimicrobial activity are needed and new alternative sources should be found. Antimicrobial peptides (AMPs) are synthesized by processes typical of the innate immune system and are present in almost all organisms. Insects are extremely resistant to bacterial infections as they can produce a wide range of AMPs, providing an effective first line of defense. The AMPs produced by insects therefore represent a possible source of natural antimicrobial molecules. In this paper, the possibility of using plasma preparations from silkworm (Bombyx mori) larvae as a source of antimicrobials was evaluated. After simple purification steps, insect plasma was analyzed and tested on different Gram-positive and Gram-negative bacterial strains. The results obtained are encouraging as the assays on Escherichia coli and Enterobacter cloacae showed significant decrease in the growth of these Gram-negative bacteria. Similar results were obtained on Gram-positive bacteria, such as Micrococcus luteus and Bacillus subtilis, which showed strong susceptibility to the silkworm AMPs pool. In contrast, Staphylococcus aureus displayed high resistance to Bombyx mori plasma. Finally, the tested plasma formulations were assessed for possible storage not only at 4 °C, but also above room temperature. In conclusion, partially purified plasma from silkworm could be a promising source of AMPs which could be used in formulations for topical applications, without additional and expensive purification steps.
Highlights
Drugs with antibiotic activity are essential in the treatment of infections; overuse of these drugs in recent decades has led to the emergence of treatment-resistant strains of bacteria [1]
Silkworm hemolymph was collected from fifth larval instar and treated to prepare the plasma by low-speed centrifugation, aliquots of the supernatants were incubated with E. coli and bacterial growth was assessed by plating and track-dilution assay (Figure 1)
Silkworm hemolymph was collected from fifth larval instar and treated to prepare the plasma by low-speed centrifugation, aliquots the treated supernatants
Summary
Drugs with antibiotic activity are essential in the treatment of infections; overuse of these drugs in recent decades has led to the emergence of treatment-resistant strains of bacteria [1]. There is an urgent need to identify new molecules and alternative sources, and to produce and test compounds with antibacterial activity as alternatives to conventional antibiotics, without inducing resistance. In this regard, antimicrobial peptides (AMPs) could be a valuable support to conventional antibiotic therapies [3,4]. Antimicrobial peptides (AMPs) could be a valuable support to conventional antibiotic therapies [3,4] These innovative and promising molecules are natural compounds showing a specific biological antimicrobial activity. They have been isolated from many species of plants, insects and other organisms, and derive directly from the mechanisms of the innate immune response [5,6]
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