Aquiluscidin, the first antimicrobial peptide identified from the Mexican dark rattlesnake Crotalus aquilus, and its shorter derivative Vcn-23 both showed potent antibacterial activity (MIC 2-8 µg/mL) with minimal toxicity to human cells.
MIC 2-8 µg/mLBoth the full-length Aquiluscidin and its shorter Vcn-23 derivative killed all tested Gram-positive and Gram-negative bacteria at these low concentrations
What the researchers found
From transcripts obtained from the skin and oral mucosa of Crotalus aquilus, researchers identified the first cathelicidin-like peptide from this species. The peptide precursor contained a signal peptide, a 101-amino-acid conserved cathelin domain, an anionic region, and a 34-amino-acid mature peptide (Aquiluscidin/Aq-CATH).
Both Aq-CATH and its shorter 23-amino-acid derivative Vcn-23 demonstrated potent broad-spectrum antibacterial activity with MIC values of 2-8 µg/mL against all tested Gram-positive and Gram-negative bacteria. At concentrations up to 50 µM, neither peptide showed significant hemolytic activity. However, cytotoxicity testing showed cell viability dropped below 65% at 25 µM, indicating a window between antimicrobial and cytotoxic concentrations that needs optimization.
Why it matters
Venomous animals are a rich source of bioactive peptides that evolution has optimized over millions of years. Cathelicidins from reptiles are particularly interesting because reptiles live in pathogen-rich environments and rely heavily on innate immunity. Discovering new antimicrobial peptides from previously unstudied species like Crotalus aquilus expands the pool of potential candidates for antibiotic development at a time when drug-resistant infections are a growing global crisis.
How the study worked
cDNA was cloned and sequenced from transcripts of Crotalus aquilus skin and oral mucosa, yielding a 566-base-pair sequence. Bioinformatic analysis predicted the peptide's structural domains. The full-length mature peptide (Aq-CATH, 34 amino acids) and a derived shorter peptide (Vcn-23, 23 amino acids) were chemically synthesized. Antimicrobial activity was evaluated through in vitro MIC assays against multiple Gram-positive and Gram-negative bacterial species. Hemolytic activity and cytotoxicity were assessed to evaluate safety.
What this study cannot tell us
This is an in vitro study only — no animal infection models were used to test in vivo efficacy. The cytotoxicity data (cell viability <65% at 25 µM) suggests a relatively narrow therapeutic window that would need improvement for clinical use. The specific bacterial strains tested and whether they included drug-resistant isolates are not detailed in the abstract. Stability, pharmacokinetics, and mechanism of action were not investigated. The study comes from a single species of rattlesnake.
How to read the evidence
This is a peptide discovery and initial characterization study with in vitro antibacterial and cytotoxicity data. While the MIC values and structural characterization are solid, the lack of in vivo testing, mechanism studies, and drug-resistant strain data limits the translational implications. This represents an early-stage discovery contribution.
When this study was published
Published in 2023, this is recent work in the active field of venom-derived antimicrobial peptides. As the first AMP identified from Crotalus aquilus, it establishes a foundation for further investigation of this species' defensive chemistry.
The bigger picture
Snake venoms and skin secretions have yielded numerous drug candidates, from blood pressure medications (captopril, derived from pit viper venom) to pain treatments. Cathelicidins represent a particularly promising peptide family because they are found across vertebrates and share conserved structural features while displaying species-specific antibacterial profiles. Each new cathelicidin discovered adds to the structural diversity available for antimicrobial drug design.
Questions still open
- Can the Vcn-23 derivative be further optimized to improve the therapeutic window between antibacterial activity and cytotoxicity?
- Does Aquiluscidin have activity against drug-resistant bacterial strains like MRSA or carbapenem-resistant Enterobacteriaceae?
- What is the mechanism of action — does it work primarily through membrane disruption, like other cathelicidins?
Common questions
Why look for antibiotics in snake venom and skin?
Could this snake peptide become a real antibiotic?
Read the original research
Aquiluscidin, a Cathelicidin from Crotalus aquilus, and the Vcn-23 Derivative Peptide, Have Anti-Microbial Activity against Gram-Negative and Gram-Positive Bacteria.
Microorganisms, 11(11)
Citation
Hernández-Arvizu, Edwin Esaú; Silis-Moreno, Teresa Monserrat; García-Arredondo, José Alejandro; Rodríguez-Torres, Angelina; Cervantes-Chávez, José Antonio; Mosqueda, Juan. (2023). Aquiluscidin, a Cathelicidin from Crotalus aquilus, and the Vcn-23 Derivative Peptide, Have Anti-Microbial Activity against Gram-Negative and Gram-Positive Bacteria.. Microorganisms, 11(11). https://doi.org/10.3390/microorganisms11112778