Antimicrobial resistance is poised to be the next pandemic. And yeah, I’m scared: I still haven’t recovered from the last one!
Can synthetic biology offer a new solution to an old problem?
Let’s hope!
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Simple Cells, Dead Bacteria
Researchers engineered chromosome-free, non-replicating SimCells and mini-SimCells to destroy antibiotic-resistant bacteria using two different killing mechanisms.
Antimicrobial Resistance: The Next Pandemic?
Antibiotic-resistant bacteria scare me.
And I’m not alone. The WHO has named antimicrobial resistance (AMR) as one of the top public health challenges for humanity. In 2019 alone, AMR was linked to over 1 million deaths, and the situation has only gotten worse since then.
By 2050, AMR could cause over 10 million deaths per year. Today, around 1 in 6 bacterial infections is already resistant to standard antibiotics, and for some strains, the number is closer to 50%.
Yeah, we’re clearly moving towards the next pandemic.
But why is this happening? The basic answer is evolution. Bacteria and other microorganisms adapt to survive the drugs designed to kill them. And this has been going on since forever!
What changed is the speed.
Human activities have made resistance evolve faster → misuse and overuse of antimicrobials in healthcare and agriculture, plus weak sanitation infrastructure.
We’re running out of effective antibiotics!
The Golden Era of Antibiotics
Antibiotics had a golden era, too.
Between the 1940s and the 1970s, we discovered 2/3 of the antibiotic classes still used today. The last new class of antibiotics was discovered in the 1980s (!), and only in 2024 did we see a promising new candidate like zosurabalpin.
So, not good.
Honestly, this is a complex issue. But this hasn’t stopped scientists!
They came up with some cool ideas:
Antimicrobial peptides that attack bacterial membranes directly. Fast-acting, with low resistance risk
Monoclonal antibodies that target microbes and recruit the immune system.
Phage therapy, which uses bacteriophages to kill bacteria without broadly hurting the microbiome.
Modified microorganisms, which use engineered microbes as therapeutic tools. The synthetic biology way!
These cool new systems come with limitations: stability, toxicity, cost, or biosafety concerns. Not great for a clinical trial…
Can we build something specific and safe?
New Weapons Against Resistant Bacteria
Today’s paper proposes an alternative!
The authors built a modular antimicrobial platform using chromosome-free, non-replicating bacterial particles called SimCells and smaller mini-SimCells. The idea is to turn these into programmable “bioparticles” that can target pathogens while remaining safe and scalable!
The team combined:
surface-displayed nanobodies to bind target bacteria
type VI secretion system (T6SS) → killing mechanism 1
enzymatic, local production of H2O2 → killing mechanism 2
The results? A single dose killed 94% of bacteria by 24 h and 99% by 48 h. And mini-SimCells could eliminate 97% of multidrug-resistant E. coli within 24 h!
Amazing! But first: what even are SimCells?
Simple Cells for Complex Problems
The platform uses two related chassis:
SimCells (simple cells): Around 1-2 μm in size, they’re produced by removing the chromosome from E. coli using inducible chromosome degradation.
mini-SimCells: They’re smaller, at around 100-400 nm in size. They’re produced from an E. coli mutant that generates minicells through aberrant division.
They both retain transcription/translation machinery, but are non-replicating and chromosome-free → much safer than “normal” engineered organisms. And both systems meet the NIH recombinant microorganism safety guidelines.
Super cool! I didn’t know about them.
And you know what’s even cooler? A similar system is currently in phase I clinical trial for cancer treatment. Yes, these bacterial-derived minicells got fast-track approval from the FDA!
This makes the translational path for SimCells much easier.
So, SimCells are mini-reactors that can’t replicate, but can do everything a cell can, including producing proteins. Promising! How do you get them to fight resistant bacteria?
Fighting Bacteria with SimCells
The engineering strategy is modular.
The team placed nanobodies on the outside of SimCells and mini-SimCells → the particles bind to specific antigens on the target bacteria. And this isn’t just for specificity. It also brings attacker and prey into close contact: exactly what the killing mechanisms need!
The two killing modes are:
T6SS-mediated killing: A contractile secretion system injects toxic effectors directly inside target bacteria.
NahG-mediated aspirin conversion: The membrane-bound enzyme converts aspirin into catechol, and catechol auto-oxidation generates H2O2 locally and continuously.
The idea is:
The nanobody brings SimCells into contact with the pathogen
T6SS rapidly kills the bacteria
NahG gives slower, but more durable chemical killing
Simple Cells Killing Bacteria
The team explored the killing systems first separately.
T6SS kills cells, fast
The authors tested SimCells and mini-SimCells expressing nanobodies and T6SS, comparing them to nanobody-only and T6SS-only. The results were great: SimCells with nanobodies and T6SS eliminated >85% of the target prey after only 6 h!NahG: aspirin → catechol → H2O2
The second mechanism gives a sustained killing effect, complementing T6SS’s rapid action. Significant bacterial reduction can already be seen after 6 h, but at 48 h it’s magical: over 99.9% of prey bacteria are dead!
And the two mechanisms can be combined.
The team engineered a consortium of two mini-SimCells types:
Attacker1: Nanobody + T6SS mini-SimCells
Attacker2: Nanobody + T6SS mini-SimCells
The system looks like this:
T6SS acts immediately
Aspirin is added later
NahG drives H2O2 production
The delayed chemical toxicity doesn’t interfere with the T6SS system!
The results are amazing: the consortium killed 94.4% of prey by 24 h and 99.3% by 48 h! And a lower dose still delivered around 90% prey elimination!
Targeting a Real Clinical Pathogen: E. Coli ST131
The major demo came next.
The team tested the mini-SimCells against E. coli ST131, a clinically important, multidrug-resistant pathogen. The team switched the targeting nanobody to Nb39 for a surface protein specific to ST131.
Yeah, the system is modular like that.
After checking the strong binding, they tested the killing. T6SS alone killed more than 70% of ST131 in 6 h, and the dual-mechanism consortium reached 97.19% elimination at 24 h and 97.58% at 48 h!
Meanwhile, ST131 was still resistant to the tested broad-spectrum β-lactams.
Oh yeah, and don’t worry. The team also checked that the SimCells systems were not toxic to human cells and that bacteria couldn’t develop resistance.
Simple Cells, Big Results
Cool idea!
I’d never heard of this SimCells system, even though it looks quite advanced. It’s clear it brings many advantages:
Specificity and efficacy
Modularity
Scalability
Biosafety
Now, of course, there are also limitations:
It’s all preclinical work
Done in controlled lab cultures (even if with real pathogenic strains)
On know surface antigens
But it’s a big step!
AMR is scary. And there’s a lot of work to stop it, but too little money behind it to bring it out there. Antibiotics are not a sexy area (maybe we should put some AI in there…). Hopefully, systems like this, already validated (and FDA-approved) for other indications, will actually make it to the market!
In the meantime, this is a cool paper! Go read it here.
If you made it this far, thank you! What do you think of AMR? And do you think these new antimicrobial approaches have a possibility? Reply and let me know!
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