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Welcome back to The Deep Dive.
Today we are opening up Chapter 15 of Lippincott Illustrated Reviews, Microbiology.
And we've got a really interesting one today.
We really do.
We're targeting a very specific group of bacteria.
We're looking at the Spirochetis.
These are, I mean, they're some of the most mechanically fascinating organisms in the entire bacterial world.
And our mission for this deep dive is to really master the big three genera in this chapter, Treponema, Borrelia, and Leptospora.
Right.
But we're not just, you know, memorizing names.
We want to understand their unique structure, why they're shaped like corkscrews, how that shape turns them into these biological drills.
And how that leads to diseases like syphilis and Lyme.
Yeah.
It's a perfect example of form following function.
Exactly.
When you look at the overview in the text, it defines Spirochetis as, you know, long, slender, gram negative bacilli.
Which sounds a little dry for what they actually are.
Sounds so boring because they're helical.
They're coiled.
And that shape, I mean, it's not just for looks.
It is their primary weapon.
You know, I was looking at figure 15 .2 in the chapter, which breaks down the anatomy, and it just completely changed how I picture bacteria moving.
Okay.
Usually we talk about flagella, right?
These little tails whipping around on the outside of the cell.
Like an outboard motor on a boat.
That's the standard model.
Right.
But these guys,
it's like they've tucked the motor inside the boat.
That is a great way to visualize it.
Figure 15 .2 shows these endoflagella, which are also called axial filaments.
Endoflagella.
Yeah.
And they aren't floating freely.
They're anchored at the poles of the bacterium, but they run lengthwise, sort of trapped between the peptidoglycan layer and the outer membrane.
So they're literally sandwiched inside the cell wall.
Correct.
And this is the critical aha moment for understanding why they're so pathogenic.
How so?
Well, when those internal filaments rotate, they don't just push the water behind them.
They whole bacterium starts to spin and gyrate.
The entire organism becomes a drill bit.
And think about the environment inside the body.
It's not just water.
You've got connective tissue, mucus.
Yeah.
These are viscous environments.
Right.
It's thick stuff.
Exactly.
A normal bacteria with an external tail is like trying to swim through molasses.
The drag is just too high.
But a corkscrew.
A corkscrew loves molasses.
It doesn't swim.
It bores.
Precisely.
This lets them tunnel through tissues and fluids that are a complete barrier to other pathogens.
That's why they are so unbelievably invasive.
Which brings us to the first of the big three.
The ultimate stealth driller.
Treponema pallidum.
The cause of syphilis.
Right.
And treponema is the study in contradictions.
On one hand, it seems incredibly fragile.
Oh, it is.
The text really emphasizes that it's extremely fastidious.
You cannot culture this thing in a cell -free system.
You can't just grow it on an agar plate.
I read it basically dies if it dries out or if the temperature shifts.
It's a real diva.
It is.
Which tells you everything you need to know about its transmission.
Because it's so fragile, it can't survive on a doorknob.
It requires direct, intimate contact to get from one warm, moist host to another before it just falls apart.
But once it gets inside, that whole diva act drops and it becomes a ninja.
A total ninja.
I was looking at the microscopy section, figure 15 .3.
It mentions you can't even see it with a normal light microscope.
It is just too thin.
I mean, we're talking about an extremely slender organism.
A normal scope just can't resolve it.
So clinically, you have to use dark field microscopy.
That's the one where the background is pitch black and the bacteria look like these glowing white spirals, right?
Exactly.
Or you can use immunofluorescence.
But the fact that it's so hard to see physically, well, that mirrors how hard it is for the immune system to see it chemically.
This was the part that blew my mind.
The text says the outer membrane lacks lipopolysaccharide.
No LPS.
That is a huge deal.
LPS is the classic red flag for gram -negative bacteria.
It's the thing that screams, I am an invader to your immune system.
And treponema doesn't have it.
Doesn't have it.
And it has very few surface proteins.
So it's basically flying in style mode.
Which allows it to set up shop and start the clock on the clinical stages.
Yeah.
And figure 15 .4 lays this out perfectly.
We start with primary syphilis.
And the hallmark lesion here is the chancre.
Okay.
And I want to clarify this because the text makes a distinction that feels really important for diagnosis.
It says the chancre is a painless ulcer.
That's the absolute key differentiator.
If a patient comes in with the genital ulcer that's painful, you're thinking herpes.
Right.
But a syphilis chancre is hard, it's indurated, and it is painless.
That just feels like a trap.
If it doesn't hurt, you might ignore it.
And to make the trap even worse, the chancre heals all by itself.
So you think you're fine.
You think, oh, I guess it's gone.
But no.
The bacteria have just replicated and drilled deeper into your system.
And they're on the move.
Exactly.
So weeks to months later, you hit secondary syphilis.
The text calls this the bacteremic stage.
The organism has disseminated everywhere.
And this is where we get that classic rash in figures 15 .6 and 15 .7.
It's described as maculopapular.
So a mix of flat spots and little bumps.
But the location is the big giveaway.
It is one of the very few diseases that causes a rash on the palms of the hands and the soles of the feet.
If you see that, syphilis has to be at the top of your list.
Right at the top.
And the text also mentions
condylamatolata in this stage.
Those are the lesions in moist areas, like the armpits or groin.
Yes.
And they are so dangerous from a public health standpoint.
They're these moist sort of wart -like lesions that are just absolutely teeming with spirachettes.
Highly infectious.
So after that rash fades, we enter the latent phase.
It goes quiet again.
Complete silence.
Sometimes for years.
But in about 40 % of untreated cases, it comes roaring back as tertiary syphilis.
And this is where the damage becomes, I mean, catastrophic.
It really is.
You get gummas.
The gummas.
Yeah, these are granulomatous lesions.
The body's immune system basically gives up trying to kill the bacteria and just walls them off in these big rubbery masses.
And they can form anywhere.
Skin, bone, liver.
Anywhere.
And then you have neurocyphilis, cardiovascular syphilis.
It attacks the aorta.
It attacks the spinal cord.
It's this slow, progressive destruction.
And we can't skip congenital syphilis?
The text says the bacteria can drill right through the center.
Usually after the 10th to 15th went of gestation, which is why prenatal screening is so critical.
Right.
Because if it's untreated.
It can cause fetal death or just severe deformities.
It's devastating.
So speaking of screening, I spent some time trying to get my head around the diagnosis section.
Talks about this two -step method.
The non -troponamal and triponamal tests.
Yeah.
It seems a little counterintuitive at first, because the first test, the screening test, it doesn't even look for the bacteria.
It looks for us.
You've got it.
Then non -troponamal tests like RPR or VDRL, they detect something called ragin.
Which is an antibody our body makes against cardiolipin.
Right.
Which is a lipid that gets released from our own cells when they're damaged by the infection.
So it's like a smoke detector.
It senses the smoke, the cell damage, not the actual fire.
That's a perfect analogy.
And because it's just detecting damage, it's not 100 % specific, but it's sensitive and cheap.
So if the smoke detector goes off, then you send in the fire department.
That's the troponamal test.
It detects antibodies that are specific to troponamal pallidum that confirms it.
And there's a really great clinical tip here.
The non -troponamal tests.
The smoke detectors.
Right.
They go negative after you treat the patient.
The smoke clears.
But the troponamal tests, the specific ones, they usually stay positive for life.
So that tells you if the treatment worked.
Exactly.
And speaking of
news is good.
Penicillin G.
The original magic bullet.
It still works.
We don't see significant resistance, which is, you know, it's a miracle in microbiology these days.
Okay.
Let's leave the stealth agent and move into the woods.
Section three covers Borrelia.
And right off the bat, the text drops this genetic bombshell.
It doesn't have a circular chromosome.
It is so weird for a
almost all bacteria have a single circular loot of DNA.
Borrelia has a linear chromosome.
That's wild.
And it has all these plasmids too.
It's just a messy complex genome.
But breaking all the rules.
But let's talk about the big one.
Long disease from Borrelia burgdorferi.
Transmitted by the Ixodes tick, the black -legged tick.
Now I want to drill down on something in the pathogenesis section.
The 24 hour rule.
Oh, this is so important.
I've heard this before, but the text actually explains why it takes a day.
Yeah, it's not an arbitrary timer.
It's a biological commute.
Commute.
When an infected tick bites you, the bacteria are dormant in the tick's mid gut.
They're not in the saliva yet.
They're just sleeping in the stomach.
Right.
When the tick starts feeding on your warm blood, that's the wake up call.
The bacteria multiply, they change their surface proteins, and then they have to physically migrate from the gut into the salivary glands.
And that trip takes time.
It takes about 24 hours.
So if you find a tick and you get it off within, say, 12 hours, you're probably safe.
The bacteria just haven't made it to the saliva.
That makes me feel so much better about doing tick checks.
But if they do make the transfer,
we get stage one erythema migrans.
The bullseye rash.
And figure 15 .9 shows this beautifully.
This big red expanding ring with a clear center.
But just like with syphilis, if you miss that early sign,
the corkscrew just keeps on drilling.
It disseminates.
So weeks later, you can get cardiac problems, neurological issues like Bell's palsy, and months later, severe arthritis.
Joint pain is a huge feature of late Lyme.
Diagnosis is serology again, right?
Yep.
And ELISA test followed by a Western blot to confirm.
And you treat it with doxycycline for early stages or ceftriaxone if it's gotten more severe.
Now Borrelia has this other cousin mentioned here that pulls off one of the greatest disguises in history.
Borrelia recurrentis.
The cause of relapsing fever because the fever comes and goes.
Over and over.
A high fever, it breaks, you feel better for a week, and then bam, it's back.
And the why here is antigenic variation.
It's brilliant.
Think of it like a bank robber changing clothes.
The bacteria show up in your blood wearing coat A.
Okay.
Your immune system recognizes coat A, makes antibodies, and kills 99 % of them.
The fever breaks.
But 1 % survive.
Because that 1 % already switched to coat B, and your old antibodies don't work on coat B.
So they multiply, the fever spikes again, and the whole process repeats.
That is exhausting.
Figure 15 .11 actually charts this out.
It looks like a roller coaster.
It's a battle of attrition.
Eventually your immune system wins or the bacteria run out of coats.
And there's a quick distinction the text makes.
Epidemic versus endemic relapsing fever.
Just remember the vector.
Epidemic is louse -borne, body lice.
That's human to human, usually in crowded conditions.
And endemic.
Tick -borne.
That's zoonotic, coming from rodents to humans by accident.
Okay, so we've done the stealth driller and the shapeshifter.
Let's finish with the water hazard.
Leptospora.
Leptospora interrogans.
I love that name.
Interrogans.
Is that because under a microscope it looks like a question mark?
Exactly.
Figure 15 .13 shows it so clearly.
These tight coils with the hooked ends.
It looks just like a shepherd's crook.
And the ticks.
We're talking about animal urine.
It's a classic zoonosis.
The bacteria colonize the kidneys of rodents, dogs, farm animals, you name it.
And they're shed in the urine.
Right.
So if that urine contaminates a pond or flood water or even just wet soil.
And you step in it with a cut in your foot or get some in your eye, the corkscrew drills in.
Exactly.
And the disease is leptosporosis.
The text describes a biphasic illness.
But the really scary version is wild disease.
Wild disease is the severe systemic form.
And because these bacteria love the kidneys and liver, the classic presentation is renal failure and jaundice.
Jaundice.
So the patient turns yellow.
Yellow skin, failing kidneys, and hemorrhage.
Yeah.
If you see that combination in a patient with a history of, say, flood exposure or water sports, you have to think leptospora.
And unlike the divatropenema, we can culture this one.
You can, though serology is still very common.
And treatment is similar.
Penicillin or doxycycline.
So we've covered the big three.
When I look back at this chapter, I don't just see a list of diseases anymore.
I see a theme.
It really is a story about mechanical advantage.
It is.
We usually think of bacteria using chemical warfare, right?
Releasing toxins.
Right.
But the spears sheds are engaged in mechanical warfare.
They've evolved a specific shape and an internal engine to physically access parts of our body that are supposed to be fortresses.
It's a great point.
It challenges how we think about infection.
It's not just about what toxins bacteria has.
It's about how the bacteria moves.
That corkscrew shape lets treponema just ignore the viscosity of connective tissue.
It lets Borrelia get from a simple bug bite into your joints and your heart.
Structure dictates function.
And unfortunately for us, the function in this case is a very, very effective drill.
It's a good reminder that in microbiology, sometimes the most dangerous weapon isn't a chemical.
It's just a shape.
A simple, elegant, and deadly spiral.
On that happy note, we will wrap up this deep dive into this Bureau of Sheddies.
Check for kicks, watch where you swim, and we will see you next time.
Stay curious.