Bacteria 1A: Gram-positive Cocci- Staphylococcus, Streptococcus (Diseases)
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in this video we’ll continue the
discussion on gram-positive bacteria specifically looking at the gram
positive cocci or circular shape within the gram positive cocci there are
a few important genus and species to discuss remember these bacteria will
stay in purple under Gram stain due to the peptidoglycan cell wall the
different proteins and sugars found in the bacterial wall allow the purple
stain to set and not be washed away by alcohol rinse when prepared on a slide
it’s also important to distinguish between the types of bacteria within the
circular shaped genre because they will have different sensitivities to
different antibiotics obviously bacterial resistance has gained a lot of
popularity lately and it’s important to know which bacteria we are treating in
order to give the most effective treatment staphylococcus and
streptococcus are the more common genus within the gram positive cocci leading
to a wider variety of ailments we also have the entero caucus which is a less
common type of bacteria but still causes severe human disease we can use
specialized tests such as hemolysis testing to differentiate between these
different species within the same family there’s alpha beta and even gamma
hemolysis hemolysis basically describes the way that the bacteria can break down
cells particularly red blood cells when put on an agar plate Staphylococcus also
has an enzyme called catalase that allows it to evade immune cells the
function of catalase is to help break down hydrogen peroxide this hydrogen
peroxide is used by certain immune cells to help fight off the bacteria and other
microbes so by breaking down the peroxide by using this enzyme the
bacteria can escape the immune system Staphylococcus generally forms in
clusters which can help separate out this genus when visualized under the
microscope streptococcus on the other hands is
usually in Chains as we also know here it is catalase positive now for the
types of diseases Staphylococcus aureus is going to be one of the larger disease
groups here it has some of the most associated infections and it’s one
you’ll hear about more commonly in clinics staph aureus has
a more dangerous variant called MRSA or methicillin-resistant staphylococcus
aureus these can cause severe infections and are resistant to many of the
antibiotics that work against normal sensitive strains of staph this is why
we have to be cautious when prescribing antibiotics to patients or over
prescribing however it’s normal vector is on the skin and the human nose so
it’s already on many of us in the general public not all of this
inoculation is MRSA but the microbe is found everywhere obviously due to this
if you have a skin abrasion nasal congestion or nasal information it can
lead to the bacteria inoculating other sites within the body one of the
diseases it can cause isn’t so intuitive based on where it lives is endocarditis
this is an infection of the inner heart lining however if you think of it cuts
in the skin whether it be a penetrating wound or surgical incision or even a
simple scrape on the elbow can lead to the staff getting through the skin once
through this barrier it may enter the bloodstream once it’s in the bloodstream
it’s catalase enzyme can help it along with other virulence factors to evade
the body’s immune system it travels through the blood until it reaches the
heart sets up shop in the heart and then you have endocarditis it can also cause
toxic shock syndrome which is one of the many skin pathologies that can be found
from this infection notice here it basically looks like the skin is peeling
off it resembles a very very bad burn and it’s caused by a particular toxin
which is a super antigen protein a the super antigen can cause fever
hypotension tachycardia since the skin is no longer there to
protect you from other bacteria that might be on or around the skin it can
lead to new infections impetigo is one of the many skin infections of
importance generally this is seen more in children you can picture a kid with a
runny nose perhaps they touch another part of their body wipe their nose and
inoculate the area with staph that was otherwise on their body it leads to a
crusty lesion often described as a honey colored crust which is a mixture of
mucus and staph aureus though their nose is the more common area to find this
infection it can also be found on the arms or legs think of a child running
through the woods scraping up their legs with branches and other plant life and
the bacteria that’s already on the skin then
infects these new scrapes and you have impetigo Staphylococcus scalded skin
syndrome similar to toxic shock syndrome in some dermatological appearances
causes a diffuse full-body reaction as well as desquamation of the skin also
the Nikolski sign can cause a top layer of skin to bubble up and slough
off which can induce further infection more specifics about the different types
of disease states will be described in next video for now let’s try to remember
all the diseases that are associated with each particular bacteria with
osteomyelitis note that anything that infects the skin and the tissue if it
goes deep enough can probably infect the bone as well alternatively it might
spread from elsewhere in the body via the bloodstream a patient may present
with a superficial skin infection from a few weeks ago maybe it’s even healing on
the outside but the bacteria is already penetrated into the wound anything that
allows for a deep enough penetration can allow the bacteria to get to the bone
tissue and then spread and cause further bone infection if staph can be found in
and around the nose then it makes sense that the oropharynx and sometimes the
respiratory system can be infected tracheitis is one of the inflammations
of the tube leading from the larynx to the respiratory system typical
presentations will consist of sore red edematous throat we also have cellulitis
on this list of common diseases for this pathogen this is yet another type of
skin infection and is important to note the differences between cellulitis impetigo and other types of skin infections so be described a little bit
more and future images that will help to pick the different depths of infection
and describe the types of infections as mentioned in the etiology for tracheitis
we can also develop pneumonia from staph aureus though not as common as many of
the other bacteria that cause pneumonia coughing and breathing can sometimes
dislodge moisture and bacteria from higher-up in upper respiratory tract
allowing it to disseminate further down into the lungs causing pneumonia next to
cover is Staphylococcus epidermidis staph epi obviously likes the epidermis
or the skin we see a lot of similar superficial skin infections but it’s not
as common as staph aureus it doesn’t have as many of the important virulence
factors these virulence factors will be covered in
more detail in the distinguishing features tier however staph epidermidis
is another cause of the severe cardiac disease endocarditis although any skin
lesion can potentially lead to an infection with this bacteria a common
demographic is an IV drug user as they’ll pierce their skin and push
bacteria living on the surface of the skin into a tissue and into the
bloodstream next and last for the staph bugs
we have Staphylococcus saprophyticus which is one of the bacteria found in
the urogenital tract thus it’s going to infect the urogenital anatomy due to
this there is a gender difference seen in the prevalence rates with this
bacteria it’s going to affect women more than men
due to the obvious anatomic differences between the genders this includes having
a shorter urethra and a decreased distance from the perianal region to the
urogenital region one of the sequela of this is a higher potential for UTI or
urinary tract infection here we see a splayed out depiction of the renal
system the urethra bladder ureters and even kidney may be susceptible to
infections spread by staph sapro a UTI may lead to serious retrograde
infections in the kidney as well called pyelonephritis which can lead to renal
scarring another sequela of upper renal system infections is kidney stones
because a bacteria is a urease producer it can lead to ammonia production and
mineral precipitation in the kidney the precipitant is called a struvite stone
so it’s not to be confused with a different kind of stone caused by a
different kind of bacteria called a staghorn stone this will be discussed in
a later module streptococcus pyogenes is also a very important and versatile
microbe like staph aureus there is a bit to cover here it is also found in the
skin and throat so there’s going to be a lot of overlap in the diseases of
presentation between this and staph aureus however we’ll focus on the main
diseases of importance first we have scarlet fever which is classified as a
systemic infection it is generally in children and some of the presentation
includes swollen red tongue general sick symptoms and erythematous dry skin
the skin color is why it’s known as scarlet fever the skin texture is dry
and likened to sandpaper in fact I saw a case like this in
Pediatrics and the skin did feel just like sandpaper the scarlet fever toxin
is called Exotoxin A and this leads to the inflammatory response that causes
the sequela seen here for anyone that has had a strep infection early on
in life rheumatic heart disease might be a concern
it is a strep-related heart disease that generally affects an individual in later
decades of life it is caused by a specific hypersensitivity reaction
called hs2 this basically causes your own immune cells to attack your heart
valves causing mitral stenosis the immune attack leads to fibrosis and
scarring of the valve as mitral stenosis ultimately leads to valve needing to be
replaced in some instances as hypersensitivity is thought to be due to
a molecular mimicry however if you’ve had a strep infection before such a
strep throat don’t fear most patients in the
developing world anyway receive antibiotics which prevents this disease
from occurring later on in life here we see impetigo again as we saw with staph
aureus I’ll save you from repeating all the
boring details just remember that it’s a superficial skin infection and it’s much
more likely to be caused by staph aureus kidney disease can also be caused by
strep pyogenes in particular post-strep glomerular nephritis like rheumatic
heart disease PSGN is caused by a hypersensitivity reaction however this
time is caused by hypersensitivity three reaction this mechanism is not from
molecular mimicry like we saw in HS2 but it’s from an antibody-antigen
complexes being formed and deposited into the tissue
when these complexes are trying to be filtered out of the blood they stick to
the renal tissue and damage the glomerulus this irritation can cause a
nephritis this complication of strep is concerning because unlike rheumatic
heart disease it is not prevented by prophylaxis with antibiotic treatment
only a small percentage of patients will develop PSGN but it can ultimately lead
to renal failure so anyone presenting with the symptoms should be monitored
closely pharyngitis is pretty self-explanatory with strep infection
the strep throat is a common vernacular outside of the medical circles most
people don’t realize that all of these diseases are caused by the same bacteria
I know I didn’t before med school keep an eye out for
throat pain redness and fever symptoms pandas is a unique type of disease it’s
actually stands for pediatric autoimmune neuropsychiatric disorder associated
with streptococcus whoo what a mouthful they’ve associated disease with a
bacterial etiology which is pretty rare basically this disease presents after a
strep infection in a child will then develop these OCD-like symptoms the
exact association is not really well understood at this point like one of the
old Harvard Dean’s said about 50% of what we teach you will be wrong the
problem is we don’t know what 50% luckily the field is always evolving intertrigo is another skin infection that we’ll see compared later on to
impetigo and cellulitis this is a superficial skin infection and
irritation generally associated with diaper rash or rash under fat flaps or
breast tissue anywhere that a lot of moisture can collect allowing the
bacteria already present in the skin to start irritating the skin our bodies
defensive walls treatment usually consists of drying the area necrotizing
fasciitis is a more serious skin infection and soft tissue infection
leading to tissue breakdown to be clear this list of diseases that we’re
covering is not by any means exhaustive these are some of the more frequent
diseases associated with the bacteria but there are always other diseases
associated with each bacteria we’re going to discuss for simplicity and the
sake of your brain these are a concentration of the most common and the
ones who are more likely to mix up clinically necrotizing fasciitis or nec
fasc is fairly distinctive and then it causes this foul-smelling tissue
necrosis this infection if not cleaned and treated soon can lead to loss of
limb sepsis and become fatal on to strep agalactiae this is another one that
we’ll see in the urogenital tract however this one is generally
asymptomatic in carriers babies on the other hand don’t necessarily have
protection yet their immune systems aren’t developed this is why strep
agalactiae is a main pathological concern in ob/gyn specialties and why
all pregnant women should be tested for colonization in their third trimester
severe neonatal infection leads to meningitis pneumonia and sepsis testing
and treatment of pregnant women is a quick and easy
preventive measure with strep pneumoniae the obvious disease is going to be
pneumonia the microbe colonizes the respiratory tract here we see a lung
field on x-ray where the entire lung is cloudy a healthy lung should be fairly
clear which appears black on an x-ray generally you don’t see an infection to
this degree assuming the infection was caught early enough with bacterial
infections you’ll see a lobular infection strep pneumo also causes the
majority of cases of adult meningitis it’s important to know adult meningitis
here as a lot of pneumonia and meningitis pathogens can look similar
and present similarly however age can be an important clue to deciding if it’s
strep pneumo or another microbe that’s causing the patient’s disease lastly
it’s the most common type of otitis media or ear infection we’ve probably
all had several ear infections in our lifetime this bacteria might be the one
to blame though there are other causes of your infection as well this one’s the
most common recurrent ear infections are not only annoying but can lead to
permanent hearing loss and even hint towards a more serious immunodeficiency
viridans strep is a group of streptococcus that doesn’t really fit in
with the others viridans is normally found in the human mouth along with many
other types of bacteria it’s interesting that the human bite is actually much
more dangerous than most animal bites including dogs and cats after dental
procedures as you probably notice from flossing you might end up with bleeding
gums these open wounds allow for hematogenous spread of bacteria that’s
already in your mouth to other parts of your body this is another pathway in
which a bacteria may latch onto the heart tissue causing endocarditis I know
we’ve had several microbes so far that caused this disease and we’ll review all
of them at the end of this module the last group to discuss in the gram
positive cocci is Group D Strep or the enterococcus enterococcus is
normal flora or the human gastrointestinal tract or GIT like most
bacteria in our guts they keep each other balanced until something throws
them out of whack in particular enterococcus can be a concern if there’s a
penetrating wound such as a stab wound or gunshot to the abdomen and I know
you’re probably getting sick of everything we’re discussing causing
endocarditis but we have one more to add to the list here
you may be thinking how am I supposed to separate all of these causes of
endocarditis how am I supposed to pick one from the other don’t worry in the
next video series we’ll go over the different ways to distinguish between
each bacteria here in the image you can see the endocardium the thin layer of
the heart muscle then you have the myocardium or the muscle that contracts
and then on the outside the pericardial sac the pericardial sac can be seen as a
white ligamentous tissue it acts to protect the heart also because enterococcus is in the GIT and close proximity to the urinary system in
females this can be another cause for UTIs this is an important non-staph
microbe that causes UTIs also if it grows out of control in the
GIT it can lead to gastroenteritis which includes cramping and diarrheal
symptoms strep bovis has more recently been moved to the group d strep as well
though the reason is not really important this actually makes it a bit
easier to remember first it’s also found in the GIT though of non-human animals
usually second it’s pathology includes the GIT so like viridans it’s kind of
similar namely it causes colon cancer pretty much all you need to remember for
this one so just a quick review I know we’ve had a lot of pathogens that cause
UTIs we’ve had a lot of diseases of the skin and soft-tissue we’ve had a lot of
bacterial infections for endocarditis so let’s just sum them up real quick
endocarditis can be caused by staph aureus staph epidermidis viridans strep
and enterococcus for UTIs you want to be thinking staph saprophyticus or group B
strep for the skin and soft-tissue infections including bone
we have cellulitis impetigo erysipelas osteomyelitis and necrotizing fasciitis
for these you want to think staph aureus and strep pyogenes here in the image you
can see the different types of diseases and the relative depth of infection in
the epidermis you’ll see a more superficial infection such as impetigo
in the dermis you will find erysipelas followed by the lower dermal infection
of cellulitis below the dermis is the fascia which leads us to necrotizing
fasciitis lastly if something makes it past the skin and deep enough or
travels through the blood and reaches the bone then we can have osteomyelitis
well that ends it for this video there was a lot of material and if it’s all
new make sure that you review everything at least one more time now that we can
put some more common diseases to a particular bacterium how can we tell if
the patient has a particular disease this topic will be explained more in our
next video tier the presentation tier in the next video in the series we’ll begin
discussing gram-positive bacillus if you appreciate the material we are creating
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