After seven hours of three horrific tests yesterday, we started up again bright and early this morning. Thankfully, in my humble opinion, we are starting the actual microbiology portion of our microbiology course, having wrapped up the immunology section. So, to celebrate the end of ridiculous detail (I'm looking at you, cytokines!), this post will be about a fairly broad idea.
Why do bacteria cause diseases? This may seem obvious, but hear me out. Viral diseases make sense: viruses depend on infecting and lysing cells for reproduction. But bacteria can live without our cellular machinery, so why evoke the wrath of the immune system by picking a fight with the local cells?
Well, first of all, many bacteria don't! These are the commensal bacteria that make up 90% of the cells in "our" bodies*. We love these guys because they do a couple important things for us. Some bacteria help us digest and/or absorb things that we can't easily digest and/or absorb on our own. But more importantly, all commensal bacteria help us out by outcompeting pathogenic bacteria from their niches. And this is the big hint as to why other bacteria need to cause disease.
Essentially, these other bacteria know (evolutionarily, not literally) that they can't win when playing by the same rules as those other extremely well adapted commensal bacteria. So, they change the rules. What do these bugs need to flourish? Water, nutrients, and hopefully a route to move on to other organisms. A great way to get these things is to make the body bring it to you through the well-intentioned but often overzealous actions of the immune system.
In broad terms, the immune system frequently starts it's fight by bringing in reinforcements in the form of immune cells riding a wave of fluid through leaky blood vessels. This fluid gives the bacteria the water it's hoping for, while the damaged cells of the surrounding tissue leak nutrients providing a great environment for the critters to multiply and thrive. If they flare up big enough to cause coughing, sneezing, diarrhea, sores, bleeding, or death, then they can spread to other people and start the cycle anew.
So bacteria often cause disease because all the peaceful positions are usually taken and you either die by the system or break the system in order to survive.
TIL: Streptococci like to grow in chains, pneumococci in pairs, staphylococci like clusters, and enterococci can do pairs or small clusters.
* They make up 90% of the number of cells not the volume of cells; most prokaryotic cells are very small compared to those of eukaryotes. To give perspective, some bacteria can live inside our cells and some eukaryotic organelles, like mitochondria and chloroplasts, are thought to be very old intracellular commensal organisms that were so symbiotic that we essentially annexed them.
No comments:
Post a Comment