A scorpion-derived antimicrobial peptide (ToAP2) killed multidrug-resistant mycobacteria in lab tests and reduced bacterial loads in mice by 90% — matching the antibiotic clarithromycin — partly by recruiting immune cells to the infection site.
~90% Bacterial Load ReductionScorpion peptide ToAP2 matched the standard antibiotic clarithromycin in clearing M. massiliense from liver, lungs, and spleen in infected mice
What the researchers found
ToAP2, a peptide from the scorpion Tityus obscurus, inhibited growth of four M. massiliense strains at a minimum bactericidal concentration of 200 µM. At this concentration, it inhibited 50% of bacterial growth in infected macrophages. In mice, ToAP2 reduced bacterial loads in liver, lung, and spleen by approximately 90%, matching clarithromycin effectiveness. Uniquely, ToAP2 also demonstrated chemotactic activity — recruiting monocytes (F4/80low Gr1), neutrophils (F4/80- Gr1), and eosinophils (F4/80+ Gr1+) — and modulated macrophage populations in infected mice, suggesting its in vivo efficacy is enhanced by immune cell recruitment beyond its direct antimicrobial action.
Why it matters
Multidrug-resistant mycobacterial infections are notoriously difficult to treat, and the antibiotic pipeline for these pathogens is thin. ToAP2 offers a dual mechanism — direct bacterial killing plus immune system activation — that could make it harder for bacteria to develop resistance. This dual action is particularly valuable against intracellular pathogens like mycobacteria that hide inside immune cells.
How the study worked
The researchers performed bioinformatics analysis of ToAP2's structure, then tested it in vitro against four M. massiliense strains to determine minimum bactericidal concentrations. They assessed its ability to kill bacteria inside infected macrophages. In vivo experiments used BALB/c and knockout mice infected with M. massiliense, with ToAP2 treatment compared to clarithromycin. Immune cell recruitment was measured using flow cytometry.
What this study cannot tell us
This is a preclinical study using mouse models, which may not directly translate to human infections. The minimum bactericidal concentration of 200 µM is relatively high, which could present dosing challenges in clinical applications. Toxicity to human cells was not comprehensively assessed. The study used a limited number of M. massiliense strains.
How to read the evidence
This is a preclinical study combining in vitro bactericidal assays with in vivo mouse experiments and flow cytometry. While the evidence is strong for an early-stage antimicrobial candidate, it has not been tested in humans.
When this study was published
Published in 2018, this study established ToAP2's dual antimicrobial-immunomodulatory activity. Further development and optimization may have occurred since publication.
The bigger picture
Venom-derived peptides represent a largely untapped source of antimicrobial compounds. ToAP2 is particularly interesting because it combines direct antimicrobial activity with immunomodulatory properties — something conventional antibiotics don't do. As drug-resistant infections become more common, these dual-action natural peptides could complement or even replace traditional antibiotics for difficult-to-treat pathogens.
Questions still open
- Can ToAP2 be modified to lower its effective concentration while retaining both antimicrobial and immune-recruiting activity?
- Would ToAP2 be effective against Mycobacterium tuberculosis and other pathogenic mycobacteria?
- What are the safety and toxicity profiles of ToAP2 at therapeutic concentrations in mammalian tissues?
Common questions
How does a scorpion peptide fight bacteria?
Could scorpion venom peptides replace antibiotics?
Read the original research
Antimicrobial and Chemotactic Activity of Scorpion-Derived Peptide, ToAP2, against Mycobacterium massiliensis.
Toxins, 10(6)
Citation
Marques-Neto, Lázaro M; Trentini, Monalisa M; das Neves, Rogério C; Resende, Danilo P; Procopio, Victor O; da Costa, Adeliane C; Kipnis, André; Mortari, Márcia R; Schwartz, Elisabeth F; Junqueira-Kipnis, Ana Paula. (2018). Antimicrobial and Chemotactic Activity of Scorpion-Derived Peptide, ToAP2, against Mycobacterium massiliensis.. Toxins, 10(6). https://doi.org/10.3390/toxins10060219