Characterization of Some Novel Antimicrobial Peptides from African Common Toad, Sclerophrys regularis

The growing number of antimicrobial resistant bacteria have necessitated urgent need for newer and effective antimicrobials. Antimicrobial peptides (AMPs) which are also called host defense peptides are promising class of bioactives found in all living thing especially amphibians. A total of 355 Sclerophrys regularis were collected and each toad was weighed and 0.02mL/g of epinephrine (1mg/mL) was administered via the dorsal lymph sac of the toad. The skin secretions were washed, lyophilized and stored at -20°C. The secretion was purified using Sephadex G-50 gel purification column. The fractions showing antimicrobial activities against Pseudomonas aeruginosa ATCC 27853, Escherichia coli ATCC 25922, Salmonella typhii ATCC 14028, Citrobacter freundii ATCC 8090, Staphylococcus aureus ATCC 25913 and Candida albicans ATCC 3147 were further purified by RP- HPFC. The purified fractions were lyophilized and m/z ratio peaks were determined using MALDI TOF/TOF MS. The sequences corresponding to the peaks were determined using Mascot Peptide Mass Fingerprint which revealed novel AMP sequences: IHAGKTVPIVK, MHLLWR and LTGQIKNGLSGR which were named Regularin-2, Regularin-3 and Regularin-4 respectively. The MICs of purified fractions were between 50 – 200 µg/mL and the antimicrobial activities were maintained when stored at -20 °C for 180 days and was significant at p < 0.05. Bioprospecting of Nigerian toad specie (S. regularis) could yield potential therapeutic AMP agents.