(5 Oct 2000, by Brian Buschman)
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To ID staphylococci you plate them, look for gram positive cocci and then either:
1) Look for bunches that look like grapes.
2) See if they are catalaze positive (staph) or neg (strep).
Staph aureus leaves a gold color on a culture on Sheep’s blood agar.
Of the three types of Staph that we need to worry about only S. aureus is coagulase positive.
Many people and most hospital staff are carriers. Infection usually only hits people with depressed defense mechanisms. It is largely controlled by washing your hands.
S. aureus has the following ways that it causes damage in a number of categories:
I) Immune effects:
a. Teichoic acid mediated adherence to cells helping to increase the infection.
b. Protein A binds the Fc region of the IgG messing up opsonization.
c. Coagulase causes host fibrin to surround itself helping protect against immune response.
d. Hemolysing - a, b, g, d types attack blood cells.
e. Leukocidins attack leukocytes.
f. Penicillinase - b-lactamase.
II) Other enzymes that Staph uses to get through tissues:
a. Staphylokinase lyses fibrin.
b. Lipase helps it colonize sebaceous glands.
c. Hyaluronidase breaks proteoglycans (hyaluronic acid).
III) It attacks tissues with:
a. Exfoliatin which causes sloughing of skin epically desquamation of palms.
b. Enterotoxins
c. TSST-1 (TSS toxin). It is similar to pyrogenic toxin of Strep pyrogens but more deadly.
Staph can cause problems with most any system including:
a) Pneumonia
b) Meningitis
c) Osteomyelitis
d) Bacterial endocarditis
e) Septic arthritis
f) UTI
It can cause gastroenteritis from the exotoxin that is left behind in the foods that we eat.
It is a cause of TSS as it releases TSST-1 that increases TNF and IL-1.
Scaled skin syndromes is from an exfoliatin toxin which causes peeling off of the skin. The scaled skin syndrome is a disease of exclusion because it’s similar that problems that can be caused by allergy.
Pneumonia after viral influenza (flu) URI. Pneumonia causes pleural effusions.
Meningitis, cerebritis and brain abscess associated with stiff neck, coma and fever.
Osteomyelitis has fever and shakes.
Acute endocarditis from sudden destruction of heart valves with a spiking fever and chills. You may not hear a murmur. Dx this type of endocarditis rather then subacute endocarditis (strep viridans) because of the rapid onset.
Septic arthritis where sepsis builds up in the synovial membrane causing joint swelling.
Skin infections are either cause by strep pyrogens or S. aureus. It is impossible to differentiate between the two so treat them with dicloxacillin which is a penicillinase resistant penicillin so it can kill the penicillin liable strep pyrogens and the penicillin resistant staph. During the skin infection you may see:
1) Impetigo (common face infection)
2) Cellulitis which is a deep skin infection that is hot, red, swollen and shines.
3) Abscesses which are pockets of swollen tissue. If it goes Sub-q it is a furuncle and if it has multiple abscesses that connect underneath it’s a carbuncle.
4) Wound infection. When wounds are infected they usually heal by second intension.
Most staph are penicillin resistant but are able to be killed by penicillinase resistant penicillins like dicoxacillin or methicillin. There are strains that are MDR to all penicillins. Treat these with vancomycin while it still works.
S. epidermidis is normally found on skin and it is coagulase negative. It is usually seen in hospital infections of catheters, IV lines, tubing and prosthetics. It also contaminates blood samples from the needle if not properly cleaned.
In the case of infection treat with vancomycin since they are usually MDR.
S. saprophyticus causes UTI in sexually active young women. Treat with penicillin. It is the only staph that is penicillin liable.
These gram positive cocci are catalaze negative and are broken into five categories that are clinically relevant. These are groups A, B, D, Viridans and S. pneumoniae. They are either a-hemolytic (group D, viridans, pneumoniae) or b-hemolytic (groups A, B).
Strep pyrogens are b-hemolytic streptococci. They cause cutaneous infections, strep throat and systemic infections.
They have the C carbohydrate used to classify them as group A but also have:
1) M proteins that increase the virulence by inactivating the compliment system. They are also antigenic so Abs form against them making them both a benefit and liability to the cell.
2) Streptolysin O is the oxygen liable enzyme that lyses WBCs and RBCs. It is also antigenic. You can order a ASO (anti-streptolysin O) test to confirm infection with strep pyrogens.
3) Streptolysin S is the oxygen stable b-hemolytic enzyme.
4) Pyrogenic exotoxin or erythrogenic toxin is b-hemolytic and causes scarlet fever. Some of them are superantigens.
5) Streptokinase breaks fibrin clots.
There are four classes of local invasion from S. pyrogens that are caused by exotoxin release.
1) Streptococcal pharyngitis which is the classis “strep throat.” Penicillin can help speed up the usually five day course.
2) Skin infections can be caused by S. pyrogens causing folliculitis, cellulitis, impetigo. These are also caused by Staph aureus so you want to treat with a penicillinase resistant penicillin like dicoxacillin to take care of either. It shows a soar throat with skin disenigration.
Necrotizing fasciitis is the “flesh eating” type of S. pyrogens. It involves strep being introduced to the sub-q fascia. It spreads rapidly causing the inflammatory response. It must be surgically removed quickly. Mortality rate is very high (>50%). Treat with penicillin G but add clindamycin to shut down the strep metabolism.
It can also be caused by staph, clostridium, gram-negative enterics or a mixed infection.
3) Scarlet fever is from strep A causing fever and a scarlet rash that covers the body but not the face.
4) TSS can be streptococcal group A. It is similar to that of Staph aureus but more severe. Treat with penicillin G and clindamycin.
There are two main systemic effects of S. pyrogens which are results of above mentioned local infections:
1) Rheumatic fever which is often a complication of S. group A, pharyngitis causing:
a. Fever
b. Myocarditis
c. Arthritis
d. Chorea
e. Sub-q nodules
f. Erythena marginatum is a red rash
It is a cause of valvular heart disease. They are susceptible bouts of rheumatic fever so they need to be put on prophylactic penicillin for the rest of their life.
After heart valve damage further damage occurs easily so before dental work you need to treat patients with amoxicillin as a preventative measure.
2) Acute post-strep glomerulonephritis is a complication of strep pharyngitis or skin infections. It is a deposit of Ag-Ab complexes on the BM of the kidney about a week after infection. Patients present with (dark urine hematouria), increased BP from increased BV and they might look “puffy.” Be suspicious if they have hematouria a week after a soar throat.
Strep agalactiae is a b-hemolytic often that is common to a woman’s vagina. Infections are usually seen in newborns. S. agalactiae is the most common cause of neonatal sepsis, pneumonia and meningitis. In young infants meningitis usually ic caused by S. agalactiae, E. coli or lysteria. It also presents with the fever but without the stiff neck in babies. They are a little more penicillin resistant but can still be treated with penicillin in most areas.
The group D streptococci are a-hemolytic and can grow in bile (esculin) and are broken into two groups based on their ability to grow in 6.5%NaCl. The non-enterocicci cannon but the enterococci (now in their own genus) do.
The non-enterococci are S. bovis and S. equines which live in the GI tract. I like to think about how I like to eat cow and horse (not really).
The enterococci include E. faecalis and E. faecium which both are normal in the GI and cause opportunistic infections in weak patients. Both are resistant to many antimycrobials. The enterococci are the only strep that are penicillin resistant.
a) E. faecalis can be treated with a combination of high dose penicillin G and aminoglycosides.
b) E. faecium is treated with vancomycin and beginning to become resistant.
Viridans are a group of a-hemolytic streptococci that live in the nasopharynx and gums. They cause three types of infections:
1) Dental infections that produce acid and cause cavities.
2) Endocarditis can be a complication of dental work. With dental work viridans can enter the blood stream and bind to the endocardium. Viridans can cause SBE (subacute bacterial endocarditis) especially in patients with existing heart problems such as congenital valve disease, mitral prolapse and rheumatic fever.
SBE is characterized by a low grade fever, fatigue, anemia nd heart murmer. You also want to look for a slow onset. Acute infection of Staph aureus will cause a spiking fever and rapid onset but SBE is slow and low grade fever.
3) Abscesses are caused by viridans that like to hide away from air. If you see strep intermedius in the blood do a CT scan to see if there is an abscess.
Strep pneumoniae is another a-hemolytic cause of pneumonia and meningitis. Pneumoniae does the same thing to parents as group B does to babies. It is very virulent
Because it has a protective capsule. The capsule is antigenic and eventually Abs will break through but there are 84 different types of capsules (8 are common) so repeat infection is possible.
You ID them by the Quellung reaction where you add antiserum and methylene blue which causes the capsule to swell. It shows an ID for the capsule.
Optochin is a chemical that blocks S. pneumoniae while it allows viridans to grow so you can identify one a-hemolytic from another.
S. pneumoniae causes:
1) Pneumonia in adults characterized by shaky chills, high fever, chest pain on breathing and shortness of breath. One or more lobes will fill with puss and bacteria which can be seen on chest x-ray. On culture of yellow-green sputum you see lancet-shaped diplococci.
2) Otitis media (middle ear infections ) in children.
3) Adult meningitis showing stiff neck.
There is now a vaccine to the 23 most common forms of S. pneumoniae that is given to the elderly, immunocompromised (HIV) or people without spleens.
Strep pneumoniae is killed with penicillin G but resistant strains are developing. Use erythromycin, chloramphenicol, cephalosporins or vancomycin for those.
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