Download Gram Positive Cocci

CLASS: 10:00-11:00
DATE: 10/21/10
PROFESSOR: Waites
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VI.
GRAM POSITIVE COCCI
Scribe: Bryant Evans
Proof: Karin Tran
Page 1 of 4
Gram Positive Cocci [S1]
a. One of the most important bacteria because they are most common type of microorganisms that cause
human disease.
Objectives [S2]
a. Read over the objectives
b. As we go through this we need to keep in mind what tests we would use to identify the different types of
organisms.
Staphylococcus [S3]
a. It is a coccus and most important in the family of Micrococcaceae.
b. Not going to talk any more about the other genera Stromatococcus and Micrococcus.
c.
-They are normal flora in the Mouth and Skin respectfully.
d.
-They can occasionally show up in samples due to contamination and cause diagnostic confusion.
e.
-Very rarely of any pathological significance.
Habitat [S4]
a. The Staphylococcus will be broken down into two main categories: S. aureus (the primary pathogen) and
then everybody else (S. Epidermis, etc). The coagulase test can separate these from all others.
b. S. aureus can normally live in a lot of places like nose, skin, and mucus membranes without trouble. Over
half the people probably half it in their nose. You can screen people for S. aureus by taking a sample from the
nose.
c. When it invades areas that it shouldn’t be at normally (like blood/bone), it can cause an abscess or infection
and possibly life threatening.
d. Many organisms have different virulent factors depending on things like host and organism ecological
relationship with one another.
e. Most common pathogenic organism found in hospitals.
f.
-Nosocomial – a pathogenic organism that is causing an infection is someone that is hospitalized.
g.
-Survives easily on inanimate surfaces and also within caregivers and the patient itself.
h. Other Staphylococci are ubiquitous on our skin also but do not cause as bad of an infection/disease as S.
aureus. However, in sick people or immunocompromised patients, the Staph can cause infections as well.
This occurs because they are enabled to breach the skin through things like catheters or IVs.
i. S. saprophyticus – Most common microorganism in the urinary tract of young women. Main cause of UTI in
young women. Not the only one though.
Lab Characteristics [S5]
a. Staph share most characteristics but also have differing characteristics that allows for identification within the
lab.
b. They stain crystal violet because of the peptidoglycan in the cell wall.
i. Appear in clumps
ii. This one slide (upper right) isn’t enough to determine what specific Staph it is
c. S.aureus is about 7 times smaller than a RBC.
d. When put on a blood agar plate, it will appear large, creamy colonies and show beta hemolytic properties: a
clearing of the RBC’s on the plate.
e. S. aureus converts mannitol to acid via fermentation and lower the pH; turning the agar from red to yellow via
the pH indicator.
f. Only a few bacteria can grow in high salt concentrations. In general, only a Staph can grow in this
environment so to separate S. aureus from other bacteria you put it on a salt agar plate. If you then see that
fermentation occurred and it changed to yellow, then you most likely have S. aureus.
g. It produces catalase. Catalase is important in that it helps separate the Staph from Strep
h. It also produces Coagulase – important virulence factor.
i. These are all characteristics that help identify S. aureus
Catalase Test for Distinguishing Staph from Strep [S6]
a. Catalase is an enzyme that many bacteria contain which breaks down peroxide into oxygen and water.
b. Why do they produce catalase?
c.
Peroxides can be toxic to bacteria (cause oxidative stress) and our bodies naturally produce peroxides as
part of our innate defense. This is why adding hydrogen peroxide to wounds helps kill bacteria.
d. The Staph cocci have evolved to circumvent peroxide by breaking it down.
e. This catalase test is a way to separate Strep from Staph.
f. *Normal board question*: What test will distinguish Staph from Strep?
g.
-The catalase of course: Staph are + and Strep are –
h.
If it the bacteria makes bubbles when added to peroxide it is catalase +
CLASS: 10:00-11:00
Scribe: Bryant Evans
DATE: 10/21/10
Proof: Karin Tran
PROFESSOR: Waites
GRAM POSITIVE COCCI
Page 2 of 4
VII. Tube Coagulase Test [S7]
a. S. aureus and few others animal staph are coagulase +. For our purposes, S. aureus is the coagulase +
Staph.
b. Used to separate S. aureus from the other Staph.
c. Coagulase is an enzyme secreted in two different ways
d.
-secreted as an enzyme into the extracellular environment by the organism
e.
-it’s also present on surface of bacteria as clumping factor.
f. Classic way of measurement of coagulase: take rabbit plasma and put it into test tube, add Staph bacteria
and if it clots (converts fibrinogen to fibrin which causes clotting), then you know you have S. aureus.
g. Why do bacteria produce Coagulase?
h.
-While within the host, its important for the organism to circumvent the host defenses. It can produce a
fibrin clot around itself to protect it from all the immune agents.
i. Takes several hours to get a result when using the rabbit plasma method.
j. A faster way in the lab is by doing the Slide Coagulase test with latex particles that have fibrinogen (a
substrate for coagulase) on the surface. Allows for clumping factor detection very quickly
VIII. Cell Wall of S. aureus [S8]
a. Many different things on cell wall.
b. It’s a successful pathogen because there are many different strains and each has different ways of causing
diseases. Not all types will express all kinds of virulence factors but many do.
c. In this diagram you can see the capsule - helps protect from host defense. The slime layers make it sticky to
help it attach and colonize in certain areas.
d. The teichoic acid act as receptors to some cells that the organism wants to attach to
e. Protein A binds Fc of IgG and inactivates it
f. The clumping factor we already talked about
g. Each one of these has important functions.
IX. Antigenic Structures & Virulence Factors of S aureus [S9]
a. The peptidoglycan will elicits part of the inflammatory response.
b.
-Stimulates the recruitment of WBC, activates complement, elicits cytokines (IL-1 and opsonic anitB)
c. For a bacteria to cause disease it needs to attach somewhere and be able to multiply there
d. Read Slide
X. S. aureus Soluble Virulence factors [S10]
a. Most of the things the protein produces once inside the body are proteins (enzymes)
b. Hyaluronidase – destroys HA (hyaluronic acid) so that it can break through facial planes, tissues, quickly and
get into the blood stream.
c. Beta lactamase – 95-98% of all Staph cocci produce this. It destroys penicillin by breaking open the beta
lactam ring and makes the antibiotics have no affect on the microorganism.
d. The altered penicillin binding proteins (PBP2’) play a large role in MRSA.
e.
- Bacteria have enzymes that catalyze the cross-linking of cell wall components. These are known as the
penicillin binding proteins. Most S aureus seen now have altered enzymes. So, these altered enzymes
are no longer impacted by the affects of penicillin or other beta lactam antibiotics.
f.
-Beta lactam drugs work by binging to these normal enzymes of binding proteins and
inactivating them. However, with the altered enzymes, this cannot occur and are therefore
resistant.
g. Fibrinolysin, Lipases, and Nucleases are all enzymes that break down things in the host cells and help the
organisms to multiply, gain nutrients for itself, and in many cases spread to other locations.
XI. S. aureus Soluble Virulence Factors [S11]
a. Many of these virulence factors depend on the phase or growth cycle and are therefore genetically
controlled. Also depends on the environment as well as the strain of bacteria.
b. Leukocidins lyses WBC’s – another factor that S. aureus has.
c. The cytotoxins released by these organisms damage the host tissues and this is what causes necrosis, or an
abscess. And abscess is a pathogenic lesion from S. aureus. It is a collection of pus from all the recruitment
of the neutrophils and all the toxins from the Staph that allow it to proliferate
d. Exfoliatin produces by some strains of Staph. It interrupts the intercellular junctions and causes the skin to
peel off. Looks like a burn and called “Scalded Skin Syndrome”.
e. Toxic Shock Toxin is associated with super antigens: toxins that actually stimulate T-cells to produce large
amounts of cytokines. This results in endothelial damage, shock, hypotension, and a rash. It was affiliated
with tampons that resulted in toxic shock syndrome.
CLASS: 10:00-11:00
Scribe: Bryant Evans
DATE: 10/21/10
Proof: Karin Tran
PROFESSOR: Waites
GRAM POSITIVE COCCI
Page 3 of 4
f. Enterotoxins – food poisoning. Don’t eat potato salad with enterotoxin. It’s just the toxin that targets the
vomiting sensation in the brain. You don’t need to actually intake the pathogen, the toxin of the pathogen is
what causes this. Can also cause severe nausea. Usually self limited to vomiting, not much diarrhea.
XII. S. aureus Diseases [S12]
a. Skin and soft tissue diseases are among the most common infections cause by S. aureus.
b. Impetigo – caused by staph as well as strep.
c. -Severe crusting of the skin on the face with an underlying inflammation.
d. Get the furuncles – the abscesses
e. Carbuncles – the furuncles that spread together and form the infection under the skin and can cause the
wound infections.
f. Cellulitis - can be seen on the eyelids
g. In some cases in can spread to the blood known as bacteremia. It can spread further into the heart valves
and potentially cause endocarditis.
h. It can also occasionally get into the brain in severe cases and cause abscesses there.
i. Occasionally causes meningitis (rare)
j. Epidural abscesses also occur by a complication of someone getting a lumbar puncture for meningitis Dx and
Staph is inadvertently introduced.
XIII. S. aureus Diseases [S13]
a. S. aureus (MRSA) is becoming an increasing cause of pneumonia in hospitals. It is also one of the leading
causes of osteomyelitis.
b. Osteomyelitis is difficult to treat – sometimes months of antibiotics are needed.
c. It can get into joints to cause arthritis and the GI tract to cause abscesses in the kidney. S. aureus is not a
common UTI pathogen, but other staph is.
d. The Toxin mediated diseases cause (main three):
e.
-Scalded skin syndrome
f.
-food poisoning
g.
-toxic shock disease
h. This carried organism can produce all kinds of diseases.
XIV. Treatment of Staph. Infections [S14]
a. Not going to talk much about treatment here. Mainly in Pharm.
b. Key facts are pointed out here.
c. Oxacillin and methicillin are used interchangeably. MRSA came about because it was resistant to methicillin,
but in the lab they no longer use methicilin since it is unstable.
d. Vancomycin is the only antibiotic that remains one of the few left that has an effect on S, aureus.
e. Over the past years, community acquired MRSA is becoming a big deal. Use to not be a problem and was
only found in hospitals, but is now found in the community.
f. Also over the last several years, new cases of Vancomycin resistant (VRSA) have come about.
g. Occurs because it acquired the vanA gene from Enterococcus.
XV. Coagulase negative Staphylococci [S15]
a. They are not as virulent as S. aureus.
b. Cause opportunistic infections
c. Can cause blood stream infection - bacteremias
d. Drug users injecting the drug can get endocarditic. Right sided in an IV drug user is common because the first
valve to get is attacked is there
e. Found often in babies and with patients with low number of neutrophils
f. Due to their slimy and sticky nature it’s hard to get rid of them. This slime also protects the bacteria from host.
Sticks to plastics and is why they are found in “line infections” in IV lines
g. White, non-hemolytic colonies
h. Don’t have the toxins like S. aureus.
XVI.
Streptococcaceae [S16]
a. Separated from staph via the catalase test.
b. There are many more gram + bacteria than the ones we are talking about.
c. The gram stain has staph (clusters) at the top with strep at the bottom.
d. Strep is most often seen in chain, or pair, formation, but is not always the case.
e. In the human body they usually grow like this.
f. On agar it is not always like this since there are so many bacteria in bunches.
XVII.
Streptococcus Classification [S17]
a. Can be classified in many ways. One of the simplest ways is the type of hemolysis they have. (alpha, beta,
gamma).
CLASS: 10:00-11:00
Scribe: Bryant Evans
DATE: 10/21/10
Proof: Karin Tran
PROFESSOR: Waites
GRAM POSITIVE COCCI
Page 4 of 4
b.
Gamma=no hemolysis
c.
Alpha=partial hemolysis and it will appear green
d.
Beta=complete clearing of the RBCs. You can read print through the plate because the RBC is gone.
e. Some bacteria have stronger beta hemolysis than others. S. aureus and some of the strep cocci show strong
beta hemolysis.
f. Among the beta hemolytic strepts, they can be further classified based on their Lancfield Groups. Lancefield
discovered that beta hemolytic strept cocci have unique carbohydrate antigens in their cell wall that are unique
and allows for identification. This is where the groups (A,B, …all the way to T) originate.
g. **Don’t need to fully understand the taxonomy here because it doesn’t serve our purpose. Know that the beta
hemolytic groups are further separated into Lancefield groups.
h. The species can be ID’d through biochemical reactions but is often not necessary and leave the taxonomy at the
Lancefield groups.
XVIII. Streptococcus Habitat [S18]
a. Can occur in many different places and is often species specific. (GI, urinary, respiratory, etc)
b. 20% of children carry group A during the winter months and is what can lead to strept throat.
c. S. pneumoniaeis one of Alpha hemolytic (no Lancefield groups), main cause of ear infections, meningitis, and
pneumonia.
d. Enterococci are important nosocomial. Normally in GI tract and is ok if it stays there. Can often be found in large
amounts in GI when being treated with antibiotics because most of the normal glut flora is killed off and it takes its
place. When outside of GI tract it causes trouble
e. Can be spread via droplets, contact, and fomites (inanimate objects)
XIX.
Lab Characteristics (of Strept) [S19]
a. Few things used to separate streps form staphs.
b. Morphology, seen as pairs or chains. Gram + stain in pairs or chains is almost always strep. The pairs are more
typical.
c. Just a little smaller than staph and will grow easily on normal agar.
d. They are capnaphilic (sp?) meaning they like CO2 ***streptococci are canophilic (CO2) loving
XX. Antigenic Structure and Virulence factors of S. pyogenes [S20]
a. Best known of Strep
b. Has many ways to produce disease. Like aureus it has learned many tricks over time. Can be related to
structures in the bacteria itself and some of the factors it actually produces.
c. It has a Hyaluronic acid capsule that prevents it from phagocytosis. Conversely it may produce high amounts of
hyaluronidase which can also destroy its own capsule. But once it reaches a high level within in a colony, it
decides that spreading is more important so it breaks down its own capsule while trying to reach new tissues by
using its hyaluronidase.
d. The group specific cell wall antigen is present on the surface as part of the cell wall. Its what separates the
microorganism. (Lancefield Group)
e. Also has beta hemolytic component that allows it to lyse RBC’s.
XXI.
Antigenic Structure & Virulence Factors of S pyogenes [21]
a. Another important component is the M Protein.
b. Important in the pathogenesis of rheumatic fever.
c. M Protein on surface of group A strep is a virulence factor keeping it from being phagocytized and binds fibrin.
d. Important in helping the bacteria cause disease.
e. We make antibodies against M protein and when we make a lot of antibody for M protein it will cause cross
reactions in the heart tissue and over time it will cause damage in the heart and affect the mitral valve.
f. Any heart disease makes you susceptible to endocarditis so that you have a subsequent of the blood stream
could possibly land on the heart valves. This is why there are guidelines for certain patients with known heart
disease.
g. Only the strains of Strep that cause strep throat is what can cause this
XXII.
Antigenic Structure & Virulence Factors of S. pyogenes [S22]
a. Scarlet fever(caused by the erythrogenic toxin) produces cellulitis in the dermal tissues.
b. Streptokinases have been known as “clot busting drugs”. They transform plasminogen to plasmin and digest
fibrin.
c. Read Slide
XXIII. Antigenic Structure & Virulence Factors of S. pyogenes [S23]
a. Patient shown with Erysipelas – more sever than impetigo.
b. The toxins that pyogenes produces are protein F, G, DPNase, C5a, etc. All these are produces by pyogenese to
help cause disease, spread in the body, and/or counteract the host defenses.
[End 51:32 mins]