00:00
Let's move on to the GI tract. So, the GI tract has got a lot of barriers in place. I mean
basically everything we put in our mouth, the mouth is a dirty place too, but everything we
put into our mouth has got some sort of microbial contamination. So we really have to have
a very robust set of barriers to prevent invasion through the GI tract. So it starts near
the top, there is acid secretions from the stomach mucosa. That low pH will kill off many
many many microorganisms, it's like dumping acid on them. There is epithelial mucus, so
lining every part of the GI tract from top to bottom. There is a thin layer of epithelial mucus
that will trap up microbes and unless they can really move quickly, they are slowed down
and kind of this mucus mock and cannot get into the cells below it. If you're down now into
the small bell, there are pancreatic enzymes and bile salts that will either eat or just
proteolytically cleave bacteria and other microbes, or will cause the balls to dissolve
because of the bile salt. As in the lungs, there are a number of antibodies secretory
immunoglobulin A and defensins and cathelicidins. Other elements that will be secreted into
the lumen will be very protective in that way. There is a very large microbiome as we're all
well aware of commensal organisms and so they make the environment relatively
non-hospitable to the new microbes setting up shops. So it's reasonably hard for a new
microbe to come in when there is already every niche in the GI tract that's been filled by
microbes that are better suited to that environment to begin with. And then, the GI tract
is constantly clearing itself. So once or twice a day depending on who you are, you are
vacating everything that's in that lumen out the other end. Okay, so if I may be successful
in getting past that barrier, what do I have to do? Well, okay, you have to be adhesive,
you do have to make enzymes that can breakdown some of the mucus so we may have to
make toxins to make the epithelium lyse or go away so that you can access what's
underneath it and get through that mucus barrier. You may have to take advantage or
may require that there be some other epithelial injury due to some other sort of trauma
or if there is diminished function. So, if we lose peristalsis, if we lose the ability to make
mucus, if we have diminished defensin or secretory immunoglobulin A production. All of
those things will allow a microbe that might not otherwise be successful to get in. And
then, you can also take advantage of antibiotics. So, antibiotics are not just targeted
against one organism. In fact, they will tend to deplete many of the bugs that are in the
microbiome. Suddenly I've taken the population that's in there of all those commensal
organisms that have filled every niche and I wiped them out with the dose of an antibiotic.
03:21
Now a new bug can come in instead of stop because there is not as much competition.
03:27
So, that maybe a mechanism by which invaders are successful in the GI tract. Let's talk
about the GU tract, genitourinary tract. So, first off, again 2, 3, 4, 5 times a day. If you
drink a lot of water that you're supposed to, then there's constant urinary flushing. So
there's not much of an opportunity, there's not much dwell time if a microbe is in your
bladder or urethra. It's constantly being flushed out. And then the vaginal vault in particular.
03:55
There is a very low pH due to glycogen breakdown by the lactobacillus, which is a normal
commensal organism in that location. So, the constant flushing in the vaginal vault, this
low pH combined to be a fairly effective barrier. So, if I'm going to be successful, what do I
have to do? Again, I have to be adhesive. Alright. I have to be able to stick. Even though
the bladder is emptying, I'm going to be sticking to that epithelium and not be flushed out
with all the urine. You may have to take advantage of other epithelial injury or diminished
urinary flow. So patients who have neuro injury and have bladder stasis because they're
not regularly voiding, now we're not having that regular flushing of the contents and bugs
can take advantage of that. And finally, particularly in women who take antibiotics that
will kill off the lactobacillus, they no longer have that low pH in the environment and then
frequently there will be a secondary infection of candida. And so a yeast infection following
antibiotics is not an uncommon phenomena and that's where the bug is now taking
advantage of the antibiotics to eliminate that nice commensal organism that lives with the
lactobacillus.