Lesson 2 - Probiotic MRSA C. elegans

Applied Molecular Cellular Biology

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🧬 Big Picture

Antibiotic resistance is a huge global problem 🚨. MRSA (methicillin-resistant Staphylococcus aureus) is especially dangerous because it resists many treatments.
Probiotics 🥛 (beneficial bacteria) might be a safer alternative. They can boost host defenses without wiping out the whole microbiota.
The tiny worm C. elegans 🪱 is used as a model to test which probiotics really work and how.

🧪 Main Findings

1. Lb21 Extends Lifespan

Researchers screened 93 Lactobacillus strains in C. elegans.
One strain, Lb21 (a mix of L. plantarum and L. brevis), made worms live 9–38% longer. 🎉
Another strain, Lb23, actually shortened lifespan. So probiotic effects depend strongly on the exact strain.

2. Lb21 Protects Against MRSA

Worms pretreated with Lb21 survived MRSA infections ~40% better than controls. 🛡️
But this protection was specific: Lb21 did not help against pathogenic E. coli (ETEC).
Lb21 didn’t block MRSA colonization directly—so the effect comes from host response, not just bacterial competition.

3. The DBL-1/TGF-β Pathway is Key

The TGF-β pathway in C. elegans regulates growth and immunity.
Lb21 protection did not work in worms lacking DBL-1, the ligand of this pathway.
Other immune pathways (DAF-16/FOXO, p38 MAPK, TOL-1) weren’t essential here.
👉 DBL-1 is essential for the probiotic effect.

4. Proteomics: 474 Proteins Affected

Worms fed Lb21 showed changes in 474 proteins.
Highlights:
- ACS-22 (fatty acid transporter) ⬆️
- VIT-2 (vitellogenin yolk protein) ↔ (moderate levels seem best)
- ASP-6 (aspartic protease in intestine) ⬇️ but still required
These three (ACS-22, VIT-2, ASP-6) were confirmed to be important for MRSA resistance.

5. Conserved in Mammals 🐷

In pig epithelial cells (IPEC-J2 line), Lb21 supernatant triggered TGF-β production.
Lb23 did not.
Suggests that the probiotic mechanism is evolutionarily conserved.

📊 Discussion Highlights

Probiotic effects are strain-specific and multifactorial.
Lb21 boosts MRSA resistance through:
- DBL-1/TGF-β signaling ➡️ immune genes (lysozymes, lectins)
- ACS-22 ➡️ stronger gut barrier + lipid metabolism
- VIT-2 ➡️ lipid transport + immune response
- ASP-6 ➡️ normal protease function during infection
Together, this creates a layered defense system 🛡️.
Interesting twist: Lb21 is a mix of two species, and the combo works better than each alone → possible synergy.

🧑‍🔬 Methods Snapshot

C. elegans strains: normal and mutants (daf-16, pmk-1, tol-1, dbl-1, acs-22, vit-2, asp-6).
Assays: lifespan, MRSA killing, CFU colonization counts, proteomics (LC-MS/MS), RT-PCR in pig cells.
Controls: OP50 (E. coli) as standard diet, Lb23 as a non-protective Lactobacillus.

Feeding worms Lb21 acts like a probiotic “vaccine” that primes their immune system through DBL-1/TGF-β signaling. This doesn’t just extend lifespan but also gives specific resistance against MRSA. The same pathway works in pigs, so there’s potential relevance for humans too. 🌍💊

Quiz

Score: 0/31 (0%)

Q0. Which probiotic strain was identified as extending lifespan and providing MRSA resistance in C. elegans?

Lb01

Lb17

Lb21

Lb23

Q1. What signaling ligand in C. elegans is essential for Lb21-mediated MRSA resistance?

DAF-16

PMK-1

DBL-1

TOL-1

Q2. How many Lactobacillus strains were initially screened for probiotic potential in this study?

120

Q3. Which of the following immune pathways was NOT required for Lb21-mediated MRSA tolerance?

TGF-β pathway

DAF-16/FOXO pathway

p38 MAPK pathway

TOL-1 Toll-like pathway

Q4. Which of these bacteria did Lb21 NOT protect C. elegans from?

MRSA 64

MRSA 43484

E. coli ETEC F18

Both MRSA strains

Q5. What was the approximate percentage increase in survival of C. elegans after Lb21 pretreatment against MRSA?

10%

25%

40%

70%

Q6. What experimental method identified 474 regulated proteins in response to Lb21 feeding?

Western blot

qPCR

Mass spectrometry (LC–MS/MS)

ELISA

Q7. Which three proteins were found critical for Lb21-mediated MRSA resistance?

ACS-22, ASP-6, and VIT-2

DAF-16, PMK-1, and DBL-1

CLEC-65, SRP-7, and VIT-3

ACS-20, ASP-1, and VIT-6

Q8. Which C. elegans tissue is mainly associated with DBL-1-mediated immune responses?

Neurons

Pharynx

Intestine

Hypodermis

Q9. What effect did UV irradiation of Lb21 have on its protective capability?

Abolished it completely

Enhanced it

Had no effect

Reduced MRSA colonization

Q10. How did Lb23 compare to Lb21 in terms of lifespan effects in C. elegans?

Increased lifespan

No effect

Decreased lifespan

Same as Lb21

Q11. In the proteomic analysis, which biological processes were upregulated by Lb21 compared to Lb23?

Protein degradation processes

Macromolecular catabolism

Lipid transport and organic acid metabolism

Defense response suppression

Q12. Which model system beyond C. elegans showed TGF-β induction by Lb21?

Mouse intestinal cells

Human fibroblasts

Pig epithelial cells (IPEC-J2)

Yeast model

Q13. What is the main proposed role of ACS-22 in the Lb21-mediated response?

Signal transduction in neurons

Intestinal barrier maintenance and lipid metabolism

Direct antibacterial secretion

Protein degradation

Q14. Which combination of Lactobacillus species made up Lb21?

L. paracasei and L. gasseri

L. plantarum and L. brevis

L. acidophilus and L. casei

L. fermentum and L. reuteri

Q15. True or False: MRSA resistance caused by Lb21 was due to reduced MRSA intestinal colonization.

True

False

Q16. True or False: The probiotic effect of Lb21 required living, dividing bacterial cells.

True

False

Q17. True or False: Lb21 increased resistance to both Gram-positive and Gram-negative pathogens.

True

False

Q18. True or False: The DAF-2/DAF-16 pathway was necessary for Lb21-mediated protection.

True

False

Q19. True or False: Proteomic analysis revealed over 2000 total quantifiable proteins.

True

False

Q20. True or False: Vitellogenins transport lipids from the intestine to oocytes.

True

False

Q21. True or False: ASP-6 was upregulated after Lb21 feeding.

True

False

Q22. True or False: The Lb21 probiotic mixture showed synergistic effects greater than each strain alone.

True

False

Q23. True or False: The TGF-β pathway is unique to nematodes and not conserved in mammals.

True

False

Q24. True or False: The increased MRSA tolerance by Lb21 can be transferred via bacterial supernatant.

True

False

Q25. True or False: GO enrichment showed that Lb21-fed worms downregulated lipid metabolism genes.

True

False

Q26. True or False: Lb21 increased expression of TGF-β in pig intestinal epithelial cells in a dose-dependent manner.

True

False

Q27. True or False: The authors suggest that personalized probiotic treatments may be more effective in the future.

True

False

Q28. True or False: Lb23 showed equal ability to colonize the C. elegans intestine compared to Lb21.

True

False

Q29. True or False: DBL-1 signaling affects antimicrobial peptide production in the C. elegans hypodermis.

True

False

Q30. True or False: The probiotic mechanism of Lb21 was completely explained by DBL-1 activity alone.

True

False