00:01
and inhibit protein synthesis. Now let's
move to salmonella. These are another
strain of enteric bacteria that cause
focal infection of the vascular
endothelium, may cause bloody diarrhea
as do some of the E. coli strains. These
bacteria infect not just the gut, but a variety
of other organs as well. They can
infect the bones for example in patients
with sickle cell disease
causing osteomyelitis. Infections with
salmonella are associated with nausea,
vomiting and diarrhea. And then another
consequence with different strains is
called typhoid fever, in which we have
systematic spread of the bacteria.
00:42
These salmonella strains are common members of
the microbiome of many animals, for
example chickens, cows and reptiles. Pet
turtles often have these strains of
salmonella in them, the turtles are fine,
in fact all these animals are not
affected by their presence, but there have
been outbreaks of salmonella
disease in children caused by contamination
from pet turtles. You buy a
pet turtle at a pet shop, you bring it home
and you have a salmonella infection.
01:12
Eggs are often contaminated with salmonella
and there have been food
foodborne outbreaks of infection from egg
products. Typhoid fever, another
manifestation of salmonella infection, is
often transmitted from a human carrier.
01:30
This can involve transmission via food or
water, a very famous example of this
kind of infection, typhoid fever, is typhoid
Mary, she was a carrier of the
bacterium, she was not sick and she was
involved in food preparation and
infected many, many people until it was
discovered that she was the source of
the infection. So typhoid Mary lived many
years ago and the solution
was to put her away in a room and not let
her interact with anyone, which is
not really satisfactory of course. But now
we understand what's happening and
we can take other measures to minimize
transmission from these carrier
individuals who still exist. So as you might
guess, these infections are
acquired by fecal-oral contamination, in the
case of typhoid Mary for example,
the bacteria, she's excreting them, if she
doesn't have good hand hygiene, she's
going to contaminate
food preparation. Bacteria make their way
to the intestine, they penetrate the
mucosal barrier, they enter M cells as well
as epithelial cells and they're
carried through to the underlying
tissues by endocytic
processes. Bacteria make their way to
lamina propria, which is again that space
underlying the epithelial sheet, in
the process
sodium chloride imbalance is introduced so
that diarrhea results and
the bacteria then spread from the underlying
spaces to the bloodstream. So
this is not something that we see with the
watery diarrhea strains, the spread
from the initial site of infection, they're
confined, but these salmonella
strains can spread typically from the lamina
propria, the bacteria enter
mesenteric lymph nodes and then from there
enter the bloodstream where they
can spread. So these infections are associated
with gastroenteritis and the
production of cytokines and an influx of
neutrophils, which attempt to clear the
infection and of course as the neutrophils
die, they release into the
stool, which has pus in it. Typhoid fever
is a kind of infection that involves
dissemination of bacteria from the intestine
using the mechanism that I
just described, but there are also non-typhoidal
systemic infections with
salmonella that are caused by food acquired
bacteria, which go beyond the
lamina propria in the intestine, get into the
bloodstream and spread to other
tissues. These are not considered infections
of typhoid strains of salmonella,
they are non-typhoidal. So let's look at how
typhoid causing strain survive and
infect. So we take them up into the gut, as
you can see on the top there,
there is an incubation period shown by the
dotted line, where the bacteria invade
the small intestine, move to mesenteric lymph
nodes and then enter the lymph
system. They can replicate in macrophages, in
various organs, so once they're in the
blood they can spread to various organs, they
are taken up into the organs,
they can replicate in macrophages of the liver,
the spleen other lymph nodes. This is an
asymptomatic phase, part of the incubation period.
Then these bacteria
are released from the phagocytes into the
bloodstream, this initiates a
septicemia or a bacteremia and that again
spread the infection to other
organs and that release is associated with
high fever. It's a typical sign of
typhoid fever. Once the bacteria are in the
blood for this second phase, they can
invade the gallbladder, and from there
they can go on and re-invade other
tissues, but the gallbladder is an important
site, because this is often a
place where chronic infection is maintained.
From the gallbladder, of
course, the bacteria can get out
through the bile duct
into the intestinal lumen and be shed,
or they can re-invade tissues, cause
ulceration of peyer patches in the gut
mucosa, be released into the stool and can
be present in the urine as well. So
there's a cycle here that you can see
from the initial infection, multiple
releases into the bloodstream and other
organs and then release and reinfection as
well. This gastroenteritis can be
treated with antibiotics, but the use of
fluoroquinolones in treatment of this
disease is controversial and if you read
the literature, you'll see people who
believe you should treat or you should not.
The systemic non-typhoidal
infections, non-typhoidal meaning not salmonella
typhi. These require antimicrobial
therapy; of course in all cases when there is
diarrhea, you also have to have oral
rehydration therapy. Typhoid fever itself
caused by salmonella typhi is very
difficult to treat. People who are carriers
of the infection cannot, the
bacteria cannot be eliminated with antibiotic
treatment, so they have to be
very careful not to contaminate others
with the bacteria in them.
So we've now gone.