Controlling the alien (bacterial) invaders

Sigourney Weaver and the killer drugs, part one: antibiotics

This is part one in Sigourney Weaver and the Killer Drugs series, where we use her movies to understand how antibiotics, antivirals, and cytotoxic drugs work. You can read the introductory post here.

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I’m not much of a science fiction nerd, but if there’s one thing I know, it’s that not all aliens are going to kill you and use your insides to incubate their progeny. If Guardians of the Galaxy can teach us anything (unlikely), it’s that organisms of mixed origins can exist together in harmony…more or less.

But not all aliens.

Some aliens are clearly no good from the get go. Like the Alien type aliens.

So lets imagine for a minute, that our body is some sort of spacecraft, and the creatures within it are the different cells. This is going to mash up Guardians of the Galaxy with Alien, so prepare yourself for carnage of any respected storytelling paradigms Sci-Fi lovers.

Humans be human

First, meet the human crew members¹. That’s a bit species-ist introducing the humans first isn’t it? I suppose I should declare my prejudice up front.

In Alien, the whole crew are human. Well, not Ash, but we don’t find that out until later in the movie. In Guardians of the Galaxy we’re just dealing with Peter. There’s nothing particularly interesting to differentiate the humans other than the usual stuff we’re all very familiar with. Underneath it all, we’re all pretty much the same when viewed through a biological lens.

The humans represent the human cells within the body. Now, just like there are different types of humans, there are also different types of human cells. These cells differ slightly in physical features and function, but they all share a common underlying biological structure.

If we think about the crude sort of view of almost all human cells you’d get from a microscope, you’d see a blob called the nucleus that contains the cell’s genetic material². You’d see the outer boundary, or cellular membrane, that defines its shape. And, if you look closely, you might see some sort of fluidy stuff within the cellular membrane called the cytoplasm.

Remember these three distinguishing features of human cells for later: nucleus and cytoplasm contained within a cellular membrane³.

Alien crew members and the bacterial microflora

Now we’ve met the humans on the spacecraft, let’s meet some of the alien crew members. Remember, There aren’t the type of alien that will threaten your life, they’re here to get the work done. To relax and play cards in between shifts, and whatever else space crew members do to unwind from their work sitting in the bridge and monitoring screens. Unless you do something to put them off balance, of course, then things might kick off and get heated.

There aren’t any alien crewmembers in Alien, but in the Guardians of the Galaxy franchise we’ve got a few to choose from in Groot, Gamora, Drax, Mantis and Nebula⁴. You can see by the picture below that there are some clear anatomical differences from the humans, beyond a gender or race aspect. There are also some obvious differences between them.

The useful alien crewmembers represent the bacterial cells that reside naturally within the body - your bacterial microflora. Our bodies are home to many bacteria that dwell in our mucus membranes (if you want to learn more about this, check out this post which talks about the inside-outside spaces in our bodies). The amount, and variety of bacteria residing within you is kept at a status quo most of the time. A useful crew on board, doing their thing and keeping things functioning.

Remember those three key features of human cells from before - cellular membrane, cytoplasm, and nucleus? Well, the physical make up of bacteria is a bit different.

Like human cells, bacteria have a cellular membrane which that holds in the cytoplasm with all its bits and bobs. in addition to this, they also have a cell wall. Some have a cell wall that’s really thick and covered in an external capsule, while others have a thin wall that’s covered in an additional membrane. Another critical difference between bacteria and human cells is that bacteria don’t have a nucleus⁵.

Critical bits to remember here: you’ve got a diverse crew of bacteria on board in your body, that most of the time is pretty happy just doing their thing trying to live their best life.

Killer aliens and pathogenic bacteria

Finally, let’s talk about the killer aliens of the Alien movie franchise that are trying to invade the space craft. Shifty little bastards trying to get in whichever way they can. One eventually succeeds breaching the airlock by attaching itself to a crew member’s face, using him as an incubator to breed their spawn and then, Bam! Alien baby forces its way out of his stomach by ripping through his abdomen. Watch out for the fully grown ones too- they’ll rip you apart.

These killer aliens represent the disease causing bacteria known as pathogenic species. Unlike the non-pathogenic bacteria of micro flora fame, pathogenic species are not here to help you live your best life.⁶

Pathogens move into a part of the body, take up residence and start wreaking havoc. Also known as causing an infection.

Most of the time, the entry point for an infection will be a break in the external surface of the body (your skin) or one of those mucous membrane inside-outside spaces in your body…whichever orifice is most inviting. The good news is, this is what the mucous membranes are made for, and they are up to the task of keeping these invaders contained and not allowing them passage through to the rest of the body. This is why most of these types of infections (like ear, sinus, respiratory infections) are limited in how long they last, even without drug treatment.

More concerning is when an invader gets into a space that is otherwise sterile, like the urine, the eye, the bones, the cerebrospinal fluid, or the blood. The last two are particularly concerning, because once they make their way into these spaces, they can take down the whole ship.

Structurally, the cells of pathogenic bacteria are the same as the non-pathogenic ones. There are the same variety of types, some with the thick wall, some without. But, because they’re often coming into the body from the external environment, there’s a chance they’ve picked up some mutations along the way. This is not a good thing.

Critical point to remember here: structurally the bad guys are the same as the good guys, which can make things tricky, especially if they’ve mutated.

“There’s gotta be a way of killing it”

So let’s consider the situation where the bad aliens from Alien invade the Guardians of the Galaxy spacecraft, and Ripley’s along for the ride. How do we eradicate the bad guys without knocking of Groot and the other useful crew members?

Contain them in the airshafts

One method, utilised in the movie Alien, is to try and contain the invaders to one area of the spacecraft - like the air shafts. Then you can either hope they gradually die off, or you can get in there with your flamethrower and turn them to cinders. This is manageable with small numbers of invaders that are sensitive to your weapon of choice.

This is the type of method used in the treatment of most of your ‘everyday’ type infections within those inside-outside spaces of the body I mentioned earlier. If it’s in an area where it’s unlikely to cause too much damage, the best approach is to watch and wait for it to sort itself out. But if it’s at a point where it’s becoming more problematic, you want to get in there with a weapon of choice that is good enough to match your foe. Enter some careful use of antibiotics.

There are a few things we want to make sure we get right if we decide to go down the antibiotic route. The first is choosing an antibiotic that’s actually going to work on the type of bacteria causing the infection. This means we’ve got to have some idea of what to expect is causing the infection in the first place. We might base this on a ‘best guess’ based on what we know are the common culprits, known as empirical therapy. Or we take a sample and see if there’s anything that grows, enabling targeted therapy.

The good news is, because the antibiotic cells are different from human cells, the antibiotic drugs we use only damage the bacteria. The bad news is, they’re not so good at distinguishing between those in your microflora and the pathogens. More on this later.

Antibiotics can either kill the bacteria cell (bacteriocidal) or stop it from replicating (bacteriostatic). The easiest way to kill a bacteria is break down it’s cell wall and capsule, but unfortunately it only works for those with the thick cell walls (gram positive species). Other antibiotics work within the internal machinery of the bacterial cell, stopping them from being able to replicate.

If an antibiotic is quite specific in the types of bacteria it kills or controls, we call it narrow spectrum. If it’s less discriminate, we call it broad spectrum. The aim of the game is to choose one that will be just broad enough, and use it at a dose and duration that’s not to little, and not to much…just right. Yes, goldilocks is back.

The reason for this approach is because these pathogenic bacterial invaders just love to evolve into more dangerous little bastards. Yes, expose them to antibiotics and they will adapt and possibly become resistant to those same drugs in the future. You’ll understand the problem of this in a few paragraphs time.

Poison them through the air shafts

OK, this method does not fit with the movie, but I feel like it would work in my Guardians of the Galaxy meets Alien spin off.

I think you could pump out some sort of chemical gas that’s poisonous to aliens, but not humans. The problem with this approach is though, while there happens to be poisonous gas on board, there aren’t any gas masks available for the alien crew (seems like an occupational work and safety issue to me). So, if you take this approach you’re going to have to accept that there’ll be some collateral damage. You’re going to take some of the good guys out with the bad guys.

Whether or not this is considered necessary will depend on the extent of the invasion. If there’s a broad scale invasion, it may be the only hope you’ve got. However, it’s a bit of overkill it we’re just dealing with a few in a confined area.

If there’s an epic infestation of Aliens proportions, things are not looking good. There are too many to confine locally. They’ve evolved to become resistant to flamethrowers and poisonous gas. There are little options available, other than to ‘nuke it from space’. OK, that’s going to destroy the entire spacecraft along with it’s crew, so we can’t do that, but we’d have to do something as close to that as possible while preserving critical aspects of life.

This relates to the concepts discussed earlier around choice of agent, dose and duration of treatment. What we didn’t discuss at that time, is route of administration.

I think this is the third or fourth time that I’m referencing this post that covers route of administration in detail, so if this is new to you, it might be worth reading it:

How do you like your coffee — espresso or enema?

As a general principle, it’s best to avoid giving any drug intravenously if you can. It just adds complications (including infection) that are better avoided. But if you’ve got a severe or system wide infection, then intravenous is going to allow you to get things under control more quickly than giving them orally.

It also allows your healthcare team to have access to some of the more ‘nuclear’ type options. The types of antibiotics that are kept for special occasions. This is why it’s so important to keep the level of antibiotic resistance under control. Because we need to make sure they work when we need them to. Resistance to these drugs is bad bad news (double bad intentional type bad, not a typo).

So if you find yourself in the situation where you’ve got a manageable, localised infection, and you’re wondering why the prescriber is hesitant to give you the prescription for antibiotics you’re expecting, remember this post. Think of it as you doing your bit to keep those killer alien bastards at bay, so we can anv anyone else having to be nuked from space because they’ve been infected with a fully resistant species.

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1. Peter would be no match for Ripley, in any way.

2. An exception is red blood cells- they don’t have a nucleus.

3. Other biological cells have these features too, like animals, plants and fungi, all of which fall under the domain of eukaryotes. To learn more about this, check Gunnar’s post The Battle of Microbial Asgard and the Rise of Complex Life.

4. I’m no biologist, but I believe Rocket is a genetically modified raccoon, so he’d fit within the mammalian/human category rather than alien. Definitely eukaryote.

5. I thought this meant the fit under the domain of prokaryotes, but I learned in the post mentioned in footnote 3 that it’s now a three domain model: eukaryotes, bacteria, and archaea.

6. The bacteria that naturally occur in your body can also cause disease if they’re relocated to an area of the body that isn’t their usual environment. For example, if the E. Coli in your lower intestines makes its way into your upper intestines…not good news. Also known as the faecal-oral route of transmission. Needless to say, always wash your hands after going to the toilet.