Diverse Families of Antimicrobial Peptides Isolated from Skin Secretions of Three Species of East Asian Frogs,Babina daunchina,Babina adenopleura, andRana omeimontis(Ranidae)

A novel membrane-disruptive antimicrobial peptide from frog skin secretion against cystic fibrosis isolates and evaluation of anti-MRSA effect using Galleria mellonella model

Antimicrobial peptides from amphibian skin secretion are a promising source for the development of alternative antibiotics against the urgent antibiotic resistance. Methicillin-resistant S. aureus (MRSA) has been found to persist in both early and late disease course of cystic fibrosis (CF). Japonicin-2LF was isolated from the skin secretion of Fujian Large-headed Frog (Limnonectes fujianensis) via the combination of cDNA cloning and MS/MS sequencing. The antimicrobial and anti-biofilm activities of Japonicin-2LF were evaluated using both reference and clinic isolated strains. The permeability of the cell membrane treated by the peptide was revealed by fluorescent staining. The cytotoxicity was examined by haemolysis, MTT and LDH assays. Wax moth larvae (Galleria mellonella) infection model was applied to assess the efficacy of Japonicin-2LF against the reference and clinic MRSA isolates in vivo. Japonicin-2LF exhibited potent antimicrobial activity, particularly against Gram-positive bacteria Staphylococcus aureus and MRSA, killing the bacteria via membrane permeabilisation. Additionally, Japonicin-2LF demonstrated the inhibition and eradication of biofilms, particularly against the biofilm of MRSA by eradicating the biofilm matrix as well as killing all the sessile bacteria. In the in vivo assay, Japonicin-2LF significantly decreased the mortality of MRSA acute infected larvae. In conclusion, it is a novel antimicrobial peptide discovered from the skin secretion of Limnonectes fujianensis, and particularly effective against both planktonic and sessile MRSA. The further in vivo study suggests that Japonicin-2LF could be a potential drug candidate to control the MRSA infection in cystic fibrosis patients.

Identification and functional analyses of novel antioxidant peptides and antimicrobial peptides from skin secretions of four East Asian frog species

In the present study, we identified 50 peptides that are classified into 21 peptide families with antioxidant and/or antimicrobial activity from Amolops daiyunensis, Pelophylax hubeiensis, Hylarana maosuoensis and Nanorana pleskei, which belong to four different genera in the Ranidae and Dicroglossidae families. These four frog species were found for the first time to express antioxidant peptides (AOPs) and antimicrobial peptides (AMPs). These peptides include seven newly discovered families daiyunin-1, daiyunin-2, daiyunin-3, maosonensis-1MS1, pleskein-1, pleskein-2, and pleskein-3. Antioxidant and antimicrobial activity assays showed that some of these peptides have good biological activities. For example, at a concentration of 50 μM, nigroain-B-MS1, and nigroain-C-MS1 both exhibited relatively strong 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonicacid) (ABTS) free radical scavenging ability, with eradication rates of 99.7% and 68.3% (nigroain-B-MS1), and 99.8% and 58.3% (nigroain-C-MS1), respectively. These peptides are potential candidates for the development of novel antioxidant or AMP preparations.