| What are staphylococci? | Gram + bacteria, they are big causes of infectious diseases in medicine, staphylo= grape like coccus = spherical.
Part of transient normal flora of skin and mucus membranes.
When skin is intact, these bacteria form colonies (colonisation)
And when skin is breached, or normal flora of skin are supressed (immunosupression) staph will take advantage and cause disease |
| Is staphylococcus always pathogenic? | it’s a pathogenic bacteria but under certain situations it’s part of the transient normal flora ,
and not all of the people have it as part of their normal flora |
| Where is staph aureus mostly found? | is usually found on the mucosa of the nose , we
talk about nostrils. |
| Where is staph epidermidis mostly found? | not a part of the transient normal flora , a part of the permanent
normal flora that is always present . |
| What are the most clinically significant staphylococcus bacteria? | Staph aureus, epidermidis and saprophyticus. |
| Talk about staph aureus. | not a part of the transient normal flora , a part of the permanent
normal flora that is always present . |
| What are the virulence factors of staph aureus? | Hemolysins: destroy the blood cells
Hyaluronidase: destroy the hyaluronic acid
Lipase: lipids
Nuclease: nucleic acid
Protein A
Biggest virulent factor = Capsule it’s found on a slime and make a biofilm that is very hard to
remove, or for the antibiotics to access it. Without this capsule, the invasiveness or avoiding the
immune system becomes more difficult. |
| Is staph aureus capable of causing sepsis? | As a gram (+) bacterium, it has a cell wall =has peptidoglycan =teichoic acid etc; so, it’s capable
of causing SEPSIS > They can induce the immune reaction: meaning the pro inflammatory
cytokines and so on |
| How does protein A contribute to the virulence of staph aureus? | IgG antibodies have an Fc portion and a Fab portion (attaches to the antigen). The Fc
portion is important in the phagocytosis mediated by antibody opsonization. However, if the protein A is attached to the Fc portion, it will replace the phagocyte and help
the Staphylococcus Aureus avoid phagocytosis and its destruction by phagocytic cells. |
| How does IgG engulf bacteria? | 2 weeks following an infection by Staphylococcus aureus, our adaptive immune
system will start producing IgG. The Staphylococcus Aureus will attach to the Fab portion, and a
phagocyte will attach itself to the Fc portion to engulf the bacteria. |
| What are some of the consequences of staph aureus infection? | Staphylococcus aureus is known to cause skin infections, food poisoning through toxins it
secretes other toxins as well that cause diseases mediated only by toxins not the bacteria.
But The bacteria itself is also capable of invasiveness so capable of bacteremia septicemia and
sepsis |
| What are the tests to identify Staphylococcus? | Catalase: Staph = catalase + (forming O2 bubbles)
Strep = catalase - (no bubbles)
Coagulase: Aureus = coagulase + (forming fibrin clot)
Epidermidis and saprophyticus = coagulase - |
| How does Staph Aureus gain resistance? | . Staphylococcus aureus has several ways of acquiring resistance. First, it acts
via plasmid mediated resistance: secreting beta lactamase that will work on the beta lactam
We have community acquired and Healthcare acquired (HA-MRSA and CA-MRSA)
There is also chromosomal resistance to antibiotics
A third type of resistance is the bacteriophage mediated |
| What is the antibiogram? | They are tests which antibiotics work on this bacterium. If we notice growth of colonies around
the antibiotic disc (a very small disc= 1cm, see next pics) this means that this antibiotic is not
inhibiting the growth of this bacteria. If no growth is detected, then inhibition did occur. |
| Give an example of antibiogram. | In the laboratory, when we find a microorganism like staph aureus in a blood/ urine
sample, we place it in a petri dish along with small discs. These discs contain antibiotics. We also
have a map of antibiotics we can use. This antibiogram with staph aureus will show that it is
penicillin resistant, methicillin resistant, clindamycin sensitive, and vancomycin intermediate. The three terminologies used with an antibiogram are: resistant- intermediate-sensitive |
| Talk about chromosomal resistance for staph aureus. | mainly methicillin on the antibiogram. We
have a gene named mecA which confers to this bacterium its resistance and enables its spread
as a community acquired MRSA. It can later acquire resistance to vancomycin and becomes
VRSA (vancomycin resistant staph aureus). It is important to know that staph itself contains
plasmids that protect it from a lot of antibiotics like tetracyclines, macrolides, amino
glycosides… |
| Talk about bacteriophage mediated resistance | . The Panton-Valentine Leucocidin (PVL) gene for example is an exotoxin virulence
factor. It destroys the white blood cells. In the nucleoid, the genetic material is integrated, and the bacteria starts
secreting the PVL toxin. At the same time, through transformation (taking genetic material
from a dead bacteria), staph can acquire the mecA gene and develop methicillin resistance. |
| How does PVL toxin cause resistance for staph aureus. | PVL toxin will bind on the PMNs (Polymorphonuclear cells) and on the epithelial cells, which
will cause a dysfunction in the mitochondria of those eukaryotic cells.
Once the PVL toxin penetrates the mitochondria, it will induce a series of chemical reactions that will eventually lead to cell necrosis (not apoptosis). Proinflammatory cytokines will be released following the necrosis of the cell. |
| To what cells are staph aureus invasive? | Staphylococcus aureus can be considered invasive to polymorphonuclear cells and epithelial cells. |
| How do cutaneous infections of staph aureus occur? | Hemolysis, hyaluronidase, lipase, nuclease and PVL toxin, will all target the different layers of the
skin |
| What is impetigo? | formation of a very superficial crusting peri-orally (around the mouth).
1. Starts with the formation of a Macule (a small spot/lesion that is not elevated).
2. It will elevate with time and become a Papule
3. It will fill with pus and become a Pustule
4. Drying of the pustules and formation of the crusts
5. The crusts will fall off and there will be no scars left. |
| What is folliculitis? | a pustular/pyogenic infection that happens inside the hair follicle |
| What are furuncules? | /Boil: it is folliculitis that involves a deeper progression inside the tissue with a small
abscess based in the hair follicle. A huge inflammatory reaction can be observed. |
| What are cabunucles? | The inflammation spreads to the surrounding follicles. There are sinus tracts that
connects abscesses under every follicle. But since the infection is in the deep layer of the dermis,
the disease can be very painful and the abscess can be so big that it will either drain to the
outside, or drain to the inside (in the blood) causing bacteremia, or it will need surgical drainage
done by the doctor followed by antibiotics |
| List in order of invasiveness and deepness the cutaneous infection types. | the impetigo is the most superficial, folliculitis is that of the follicle it is not painful nor deep,
there are no swelling. But when we talk about furuncles and carbuncles there’s a possibility to
have an invasion to the deeper tissue caused by bacteremia |
| What occurs when we have a deep infection? | the deeper we go the more the
non-specific symptoms increase which means the patient might have fever if he has a huge
carbuncle because this is due to the inflammatory cytokines that are spread somehow into the
blood after this deep infection whereas in the impetigo (crusting) I will definitely not have fever
that is due to inflammatory cytokines because it is just the epidermis that is being damaged |
| What is the Hordeolum? | This is in the ophtalmo: called Stye or Hordeolum. It is commonly seen and resolves on its own and it is the folliculitis of the eyelashes caused by the staph aureus. |
| What is a regular abscess? | When you have an abscess normally it is a sign of inflammation (red, warm, painful, swollen),
the skin is full of puss (loss of function of this piece of skin) and this one should be drained and
as you see this puss is on the inside. Once you do a very small incision, the puss will get out of
the abscess |
| What is a cold abscess? | usually in people who are immunosuppressed (eg: takes corticosteroids, or
leaving HIV untreated) he will have an infection with staphylococcus. The destruction will happen
because the bacteria is destructive (it will destroy the tissue) but to the outside world, the body
(inflammatory response) is not strong enough to show me how bad the situation is.
It is cold because it looks less inflamed, no puss, no warmth |
| What treatment is used for abscesses? | Same treatment for both should be done but we should also investigate the immune suppression
(reason) in the cold abscess |
| Why are cold abscesses dangerous? | Cold abscess is an abscess that already started but is not showing which makes it worse because
the disease might be ignored by the patient. |
| What is the exfoliative toxin? | Toxin released by staph aureus, causes baby impetigo it will work on the epithelial
junctional cells and will leave a huge surface of the skin of the baby exposed which will increase
risks of other infections. |
| What is SSSS? | Staphylococcal Scalded (burned) Skin Syndrome (also known Ritter’s Disease): The toxin A is coded by a
bacteriophage and the B is coded by a plasmid. SSSS disease start in the perioral area and then it will spread to the whole body |
| Can we detect bacteria on px's skins? | This skin changes are interesting because we can’t detect bacteria on the patient skin. It’s only
the exfoliative toxin working without the presence and the multiplication of the bacteria |
| How do we recover from skin infections caused by staph aureus? | The recovery is spontaneous: the patient will recover on his own we just need to prevent
superinfections and to give enough fluid and protect the baby from deteriorating. The rash will
heal leaving non scars behind it |
| Talk about the food poisoning caused by staph aureus. | Staph aureus besides causing skin infections and having toxins that cause SSSS also has a toxin
that cause food poisoning
Example: enterotoxin A and enterotoxin B. The B can be found in meat dishes, ice cream and custard filling. The B is more important and dangerous than A because B is heat stable and resistant to the digestive enzymes. |
| How does food poisoning caused by staph aureus visible? | The toxin after it was ingested by food will have few hours (incubation period) before the
symptoms appear. The symptom is only vomiting. The vomiting is because the enterotoxin
work on the vomiting center in the brain. We can have in some cases diarrhea and abdominal
pain but not fever |
| How do we treat food poisoning caused by staph aureus? | The treatment is symptomatic: we give the patient fluid and electrolytes
It is chromosomally mediated (enterotoxin) |
| What is the third type of toxins released by staph aureus? | TSST1 (the two others are enterotoxin and toxin)TSST1 acts like an endotoxin. It works on the skin causing the rash and cold skin because of the dilation of the vessels. And the dilation of the vessels causes tachycardia to compensate the decreased blood flow to the heart and will also work on hypothalamus to increase the temperature causing the fever. |
| Give an example on toxic shock syndrome. | A 32 years old female is a surgeon and has long time of work in the operating room.
After a break she had to return to the operating room. She started to had a headache and fainted.
She had a hypotension with tachycardia. Rashes started to appear on her skin and the patient started to have signs of a shock. Its like a septic shock but here there is no bacteria that is multiplying and causing the septic shock.
Because the female surgeon was putting tampons and not changed on time there was growth of staph aureus and it started to secrete TSST1 in the vaginal area. The toxin in the genital area passed to the blood (bacteria are still on the tampon/pad, it is the toxin that spread). This is toxemia (not bacteremia) |
| What are the symptoms of a toxic shock? | Headache, Fever, Redness of eye, Racing Heart, Rashes on hand and feet, Fainting, Low blood pressure
Also caused by strep pyogenes. |
| What are the consequences of staph aureus infection? | 1. Skin infection
2. Scalded Skin Syndrome
3. Food poising (Enterotoxins)
4.toxic shock syndrome
5. effects that are caused by bacteremiaWhen staph. reaches the blood it can virtually go to any other distant organ. |
| How does acute endocarditis occur due to staph aureus infection? | When staph. reaches the blood it can virtually go to any other distant organ. If it went directly to the heart and attached itself on the endocardium of the heart, it will
cause acute endocarditis. Endocarditis is a very dangerous disease because the inside layer
of the heart usually is infected, the staph aureus might multiply and do vegetations on the
valve of the heart |
| How does pulmonary infection due to staph aureus infection occur? | It can cause pulmonary infections like pneumonia. However staph. aureus pneumonia is
commonly caused after a viral infection (post viral Example: Influenza virus) it will cause
destruction of columnar ciliated cells and goblet cells which will lead to exposure of surface
tissue and we won’t have a working mucocilliary escalator |
| Can staph aureus cause an aggressive infection? | the staph aureus can establish an aggressive infection that I can sometimes call necrotizing
pneumonia.
It can also cause a pulmonary abscess and empyema |
| What is an empyema? | When we start reading x-rays, we will see that the pointy end of the lung is not found and
there is a huge amount of puss inside the pleural cavity
(Biconvex displacement is visualized in X-rays in case of empyema) |
| How is empyema treated? | It requires antibiotics to be treated but sometimes it isn't enough. Sometimes we need to
insert a chest tube in order to drain this puss. |
| What is thoracocentesis? | to take a sample from fluid inside the chest and send it to laboratory analysis. |
| Give an application of thoracocentesis. | If we take a sample via thoracocentesis from a patient suffering from empyema, I will visualize
the gram +clusters on the gram stain and if I cultured them, I will isolate staph aureus. And
when I culture the staphylococcus aureus, I request an antibiogram in order to know which
medication I should give |
| What is osteomyelitis? | is when bacteria go to the blood and then goes inside the marrow of the bone |
| Can staph aureus infection cause meningitis? | Staph aureus can also go the brain and cause meningitis which is the inflammation of the
meninges of the CNS. |
| How can a carbuncule lead to further symptoms? | Patient could have carbuncle skin infection and because of it the bacteria will go and spread to
distant tissue. (thanks to the carbuncle, the bacteria can travel to distant organs) |
| How is pneumonia due to staph aureus acquired? | Usually pneumonia occurs post-viral infection. This means that after a viral infection the
ciliated apparatus becomes damaged. Then staph aureus takes advantage of the situation
leading to a bacterial infection causing pneumonia |
| What is hemolysis? | After streaking and adding staph aureus bacteria on a petri dish, Dots (colonies) of staph aureus are found, surrounded by a halo of clear agar, this is called the zone of hemolysis, where hemolysins secreted by the staph aureus are found. |
| What is the mannitol salt agar? | an agar containing mannitol and NaCl (7.5%). staph aureus growth occurs in this agar, they are usually golden (aureus=gold) but the bacterial colonies appear in yellow.
Staph aureus vs. Serratia marcescens on MSA: staph aureus appears yellow when incubated in MSA while Serratia appears orange. |
| How do we prevent Staph aureus infection? | To prevent staph aureus infection, proper hygiene and sterile surgical instruments are required (in reality sterility and hygiene are not properly happening, so staph aureus may be transmitted to people through contaminated instruments, or infected health care providers.) |
| How do developed vs underdeveloped countries deal with resistant staph aureus infections? | In well-developed countries, if someone is infected by MRSA or VRSA or complete drug resistance they isolate infected individuals and start taking samples to look for the most proper way of dealing with the situation, unlike other less fortunate countries where these kinds of nosocomial infections may lead to an outbreak. |
| Why is there no vaccine for staph aureus? | There is no vaccine for staphylococcus aureus because it has 7 or 8 ways of resistance including beta lactamase, MIC A, and VRSA. And it’s hard to predict mutations that may happen.
What doesn't kill you mutates and tries again. |
| What is MSSA? | methicillin sensitive staph aureus (it is not resistant to methicillin) |
| What is MRSA? | methicillin resistant staph aureus
o HA (hospital acquired) treated by vancomycin intravenously
o CA (community acquired) treated by clindamycin, Bactrim and doxycycline |
| Can we use serology to detect staph aureus? | is useless in detecting staph aureus because it is hard to detect them especially that they have a capsule and protein A. |
| Where is staph epidermidis found? | is part of the resident normal flora and it can cause subacute endocarditis.
Normally we have it everywhere on the skin, but the growth has also a slime (or biofilm).
staph epidermidis is at peace with my body, but it will take opportunity of the introduction of catheters, valve replacements or knee prosthetic joint. And on these surfaces the bacteria will spread by bacteremia, and attach itself to these foreign objects. |
| How do we treat staph epidermidis? | we should give antibiotics like rifampicin (that can move inside the biofilm) |
| What is the difference between acute and subacute endocarditis? | Acute endocarditis can happen because of staph aureus suddenly (acutely)and the patient won't suffer from anything or will suffer from valve problems, but subacute endocarditis happens slowly over the course of few months and necessitates the presence of a valve that’llreplace the damaged valve or any opportunity of a foreign body that it can be attached on |
| What is staph saprophyticus? | The last one of staph it is called Staph. saprophyticus it can feed on dead tissue , sapro= dead tissue usually we can see in transient normal flora in GI tract or urinary area but because in females there is proximity between the GI orifice and the vaginal orifice> |
| When does staph saprophyticus infection occur? | the Staph saprophyticus can cause a local spread on the outside and move to the UT to cause cystitis , acute cystitis is the inflammation of the bladder usually it happens in sexually active young females but it is not an STI it is just a UTI , when we talk about STI this means that the organism
is mainly if not absolutely transmitted through sex like gonorrhea and chlamydia and heaemophilus ducreyi . Staph it is just a simple UTI |
| What is Dysuria? | Painful urination. |
| What is pyuria? | we have puss in urine or we have WBC in urine |
| How do we differentiate between staph epidermidis and saprophyticus? | Both of Staph epidermidis or saprophyticus are catalase + and coagulase – these is why the only way which I can differentiate them from each other is that when I incubate them on agars or petri dishes, I can put a certain antibiotic disc (the disc is about 1 cm in diameter).anitbiogram using disc containing novobiocin, the saprophyticus is resistant to the novobiocin but the epidermidis is sensitive to novobiocin |
| What is streptococcus? | Streptococcus is a chain of cocci grouped next to each other. The streptococci are gram+, facultative anaerobes. They are fastidious which means they are picky in their growth. If I don’t provide them with the factors required for their growth, they won’t grow resulting in a
false negative culture. |
| List some streptococcus bacteria. | Streptococcus pyogenes or Streptococcus A or Group A streptococcus (GAS) is the most
important type to be discussed.
Streptococcus agalactiae causes certain problems in children.
Streptococcus pneumoniae causes pneumonia. (Inflammation of alveolar lungs)
Viridans streptococci
Enterococcus |
| How do we classify streptococcus bacteria? | Classification of streptococcus is done based on the capsular antigens on the outside via Lancefield classification (A, B, O) such that Strep pyogenes are type A, Strep agalactiae are type B and Strep pneumoniae are type O (no Lancefield antigens) |
| What are the types of hemolytic reactions? | 1. Alpha: The color becomes green because blood hemoglobin is broken down into
methemoglobin which is the metabolite responsible for the green color. Here we have
partial hemolysis.
2. Beta hemolysis: Complete hemolysis, blood becomes transparent.
3. Gamma hemolytic: there is no hemolysis |
| What is the best way to classify bacteria? | The best way in classifying bacteria is genetic typing. When the classification we are performing
is based on nucleic acids and genetic information, the results are more reliable and accurate.
However, genetic typing cannot be purely used in clinics. More practical ways are still used such
as Lancefield and hemolytic classifications. |
| How do we identify strep agalactiae? | Streptococcus agalactiae may cause abortion. To identify this bacterium in a pregnant woman we say that we are testing for GBS. (Group B Streptococcus) |
