Invertebrates are a source of anti-bacterial compounds

• Main Author: Salwa, Mansur Ali
• Format: Thesis
• Published: 2020
• Subjects: QR Microbiology; RA Public aspects of medicine; RC Internal medicine
• Online Access: http://eprints.sunway.edu.my/2387/

Infectious diseases remain a significant threat to human health, contributing to more than 17 million deaths, annually. The evolution of multidrug-resistant bacteria is an important factor contributing to the global antimicrobial crisis, hence there is an urgent need to develop novel antimicrobials. Discovery of antimicrobials from animal sources is an area superficially explored. Insects such as flies and cockroaches come across pathogenic bacteria routinely, yet thrive in polluted environments. Others, such as centipedes and worms feed on germ-infested insects and rodents. Logically, such species must have developed an approach to protect themselves from these pathogens. We hypothesized that animals living in a diverse natural habitat with stressed environments are potential sources of antimicrobials. In this study, we selected a broad range of invertebrates from terrestrial and marine environments and tested their antibacterial activity against drug-resistant bacteria. These include cockroaches, tarantulas, earthworms, superworms, and centipedes from terrestrial environments; and prawns, lobster, mud crab, mussels, and clams from marine environments. Animals were dissected and water-soluble extracts were prepared. Next, antibacterial assays were performed to elucidate the efficacy of the lysates against bacteria. Host cell cytotoxicity assays were performed to determine the selective toxicity of extracts towards bacterial cells. Chemical characterization of selected extracts was analyzed using spectra obtained with liquid chromatography-mass spectrometry on Agilent 1290 infinity liquid chromatograph, coupled with an Agilent 6460 triple quadruple mass spectrometer. Cockroaches, centipedes, tarantulas, prawns, lobster and mud crab were found to possess significant antibacterial activity against tested bacterial pathogens. The brain extracts of cockroach exhibited more than 90% bactericidal effects against both MRSA and neuropathogenic E. coli K1. Using cytotoxicity assays, it was observed that pre-treatment of bacteria with brain lysates inhibited bacterial-mediated host cell cytotoxicity. Chemical characterization of cockroach brain extract has identified 5 compounds from water-soluble and 15 compounds from methanol soluble extracts. These compounds contained various functional groups such as isoquinoline group, chromene derivatives, thiazine groups, imidazoles, pyrrole-containing analogs, sulfonamides, furanones, and flavanones which are known to possess broad-spectrum antimicrobial, anti-inflammatory, anti-tumor, and analgesic properties. Similarly, red-headed centipede’s haemolymph, gut and muscle extract showed remarkable antibacterial activity against MRSA, S. pyogenes, B. cereus, E. coli K1, S. enterica, K. pneumoniae and S. marcescens. Interestingly, centipede’s haemolymph extracts inhibited bacterial mediated damage to human cells. LC-MS characterization of centipede’s haemolymph extracts revealed the identification of 12 compounds that belong to various groups including cyclohexenones, sulfonic acids, sesquiterpenoids, sulfur-containing dithiolethiones, amines, phthalides, fatty acids, etc. and are known to possess broad-spectrum biological properties. Reported biological activities of the identified compounds possibly explain the survival of these species in harsh and challenging environments. Moreover, peptide characterization from centipede’s haemolymph revealed the presence of 1051 peptides, including 104 predicted antimicrobial peptides. Selected purified molecules were tested for their antibacterial properties against MRSA and neuropathogenic E. coli K1. All the compounds tested, showed significant broad-spectrum activity against selected Gram-positive and Gram-negative drug-resistant bacteria. Interestingly, tested compounds were non-toxic to primary human cells suggesting their selective toxicity towards bacterial cells. Hence, it is demonstrated that in addition to antimicrobial peptides, small molecules/secondary metabolites also play a key role in exhibiting antibacterial activity, which could be of potential pharmaceutical significance due to their selective toxicity and better pharmacological properties. Therefore, this area of research should be extensively explored to determine the mechanism of action of these molecules and their in vivo efficacy in the biological system.