Strep

Rheumatic fever

with the advent of penicillin, rheumatic fever is now uncommon. It usually strikes children 5-15 years of age. When it occurs, it has been shown to follow untreated strep pyogenes pharyngitis (but NOT skin infections). The 6 major manifestations of rheumatic fever: 1. fever 2. myocarditis 3. Joint swelling (arthritis) 4. Chorea ( uncontrolled dance like movements of the extremities) which usually begins 2-3 weeks after the pharyngitis. 5. Subcutaneous nodules 6. Rash called erythematous marginatum because it has a red margin that spreads out from its center.

enterococci infections have the following characteristics and manifestations

∙It can be found in the elderly or debilitated ∙It involves the mucosal or epithelial layer being disrupted. This can occur in catheterization, as this organism is normally part of the gut ∙Treatment of broad spectrum antibiotics can lead to infections. This leads to it "growing up," as it is often resistant to these antibiotics and can take up the space and nutrients of the other normal flora ∙It manifests itself clinically in urinary tract infections, nosocomial bacteremia, bacterial endocarditis, and peritonitis

Necrotizing Fasciitis

"Flesh eating strep" This strep pyogenes infection has actually been around for years but may indeed be on the rise. Certain strains have M proteins that block phagyocytosis, allowing bacteria to move rapidly through tissue. Strep enter through a break in the skin caused by trauma and then follow a path along the fascia which lies between subcutaneous tissue and muscle. Within a day the patient develops swelling, heat, and redness that moves rapidly from the initial skin infection site. A day later the skin color changes from red to purple to blue, and large blisters (bullae) form. Later the skin dies and muscle may also become infected (myositis). This infection must be recognized early and the fascia surgically removed. Rapid antibiotic therapy is crucial. Group A beta hemolytic strep are still sensitive to penicillin G. Mortality rate high.

Certain species of strep can either completely or partially hemolyze red blood cells. The strep are divided into 3 groups based on their specific hemolytic ability:

1. Beta-hemolytic: strep completely lyse the RBCs, leaving a clear zone of hemolysis around the colony example: S. pyogenes 2. Alpha-hemolytic: strep only partially lyse the RBCs, leaving a greenish discoloration of the culture medium surrounding the colony. The discolored area contains unlysed RBCs and green colored metabolite of hemoglobin. Example: S. pneumoniae 3. Gamma-hemolytic: strep are unable to hemolyze the RBCs and therefore we should really not use the word hemolytic in this situation. Example: E. faecalis

The viridans strep cause 3 main types of infection:

1. Dental infections 2. endocarditis 3. abscesses

Strep pneumococcus are distinguished in the lab by:

1. Lancet-shaped diplococcus 2. Optochin sensitivity 3. Bile solubility 4. Quelling reaction: When pnuemococci on a slide smear are mixed with a small amount of anti-serum (serum with antibodies to the capsular antigens) and methylene blue, the capsule will appear to swell. This technique allows us to detect the presence of a capsule. The capsule swells during this reaction, which shows that it is present. 5. Pneumococcal C polysaccharide is detected in the urine This is better than using a sputum test, as a sputum test would require one to swallow something to cough up the sputum Antibiotics and polyvalent vaccines for the elderly and children are involved in treatment and prevention

Strep pyogenes can also cause 2 delayed antibody mediated diseases:

1. Rheumatic fever 2. Glomerulonephritis

Strep pyogenes cause 4 types of disease by local invasion and or exotoxin release

1. Strep Pharyngitis 2. Strep Skin infections 3. Scarlet fever 4. Strep toxic shock syndrome

They have many different virulence factors of strep pneumococcus

1. They have a capsule 2. They have surface protein adhesins This involves the release of cell wall components, which leads to the inflammatory response 3. They possess pneumolysin, an exotoxin that creates pores in ciliated epithelial cells and kills phagocytes. This exotoxin activates complement, which leads to the migration of inflammatory cells and tissue damage. 4. It also possesses secretory IgA protease because it is on mucosal surfaces

What components of strep pyogenes cell wall that are antigenic include:

C- Carbohydrate: The C carbohydrate was used by Rebecca lancefield to divide strep into groups. Strep pyogenes has the "Lancefield Group A" type of C carbohydrate. M protein: This is a major virulence factor for the group A strep. It inhibits the activation of complement and protects the organism from phagocytosis. However, it is also the weakest point in the organism's defense, because plasma (B) cells generate antibodies against M protein (opsonization), aiding in the destruction of the organism by macrophages and neutrophils.

Clinical manifestations of strep pneumococcus

Clinical diseases involve with this strain include: 1. *Typical lobar pneumonia*: S. pneumoniae is the leading cause of this disease 2. *Meningitis*: S. pneumoniae is the most common cause of this disease in children and young adults 3. *Otitis media* 4. Sinusitis 5. Bacteremia

Viridans Endocarditis

Dental manipulations send showers of these organisms into the bloodstream. Subsequently, they can implant on the endocardial surface of the heart valve, most commonly on a previously damaged hear valve. These bacteria produce an extracellular dextran that allows them to cling to cardiac valves resulting endocarditis.

Strep and Staph are both what?

Gram positive.

Group B lancefield Strep

Group B is Streptococcus agalactiae

Group C lancefield Strep

Group C and G are S. milleri and S. dysgalactiae These bacteria can cause Strep throat, but other than that we will not discuss them

Group D lancefield strep

Group D is the Enterococci, such as E. faecalis and E. faecium, and Nonenterococci, such as S. bovis. S. bovis can cause endocarditis associated with gastrointestinal neoplasms. Nonenterococci will be talked about more in systems

Step pneumococcus

In the literature, it has become a member of the Viridans group within the last five years They are a gram positive diplococci that is *lancet shaped* in short chains. Clinically, this is a great determining factor of this bacteria strain. The first picture on the left show the lancet-shaped diplococci. They are *alpha-hemolytic* on blood agar

How is enterococci identified in the lab?

It grows in 6.5% salt concentration It grows at 42°C It grows in the presence of 40% bile salts →It is identified by a positive PYR test which demonstrates the presence of L-pyrrolidonyl-arylamidase, a compound for which S. pyogenes is also positive However, no other Group D Strep is positive for this test

Streptococci toxic shock syndrome

It is now clear that beta-hemolytic group A strep can cause toxic shock syndrome like staph aureus. Similar to scarlet fever, strep toxic shock syndrome is also mediated by the release of pyrogenic toxin.

Does streptococci possess catalase?

No, streptococci do not posses catalase, however staphylococci do possess catalase. Catalase converts hydrogen peroxide which is used by macrophages and neutrophils into water and oxygen.

There are 2 important lab tests to identify pneumococcus: Optochin sensitivity

Optochin sensitivity: Strep pneumococcus is an alpha-hemolytic (partial hemolysis-greenish color) but Strep viridans is also alpha-hemolytic! to differentiate the two a disc impregnated with optochin is placed on the agar dish. The growth of strep pneumoniae will be inhibited, while strep viridans will continue to grow.

Strep pyogenes Skin infections

Skin infections can range from folliculitis, pyoderma, erysipelas, cellulitis, and impetigo. These skin infections can also be caused by Strep aureus. Therefore treatment for these infections consists of a penicillinase resistant penicillin like dicloxacillin, which covers both group A beta hemolytic strep and staph aureus.

Viridans Dental infections

Some of the viridans strep, especially S. mutans, can bind to teeth and ferment sugar, which produces acid and dental caries (cavitites)

How can you tell the difference between strep and staph on gram stain?

Streptococci line up one after the other like a strip of button candy, while staphlococci appear as clusters that can be visualized as a cluster of hospital staff members posing for a group shot. When strep grow they divide in one plane, such as chains or pairs

Streptococcus pneumoniae

Streptococcus pneumoniae is an organism that is involved in bacterial pneumonia

Group A lancefield strep

Streptococcus pyogenes

Beta-hemolytic Group A strep (Strep pyogenes) also have many enzymes that contribute to their pathogenicity:

Streptolysin O: The *O* stands for oxygen labile as it is inactivated by oxygen. This enzyme destroys red and white blood cells and is the reason for the beta-hemolytic group A strep's beta hemolytic ability. This enzyme is also antigenic. Following pharyngeal or systemic beta-hemolytic group A strep infection, anti-streptolysin O (ASO) antibodies develop. On the wards you may order ASO titers on a patient's blood to confirm recent infection. Streptolysin S: The *S* stands for oxygen Stabile. This is also responsible for beta-hemolysis but is not antigenic. Pyrogenic exotoxin: also called erythrogenic toxin, this is found in only a few strains of beta hemolytic Group A strep, but when these strains invade they can cause scarlet fever. Some strains produce pyrogenic exotoxins that are superantigens. The exotoxins directly stimulate T cells to pour out inflammatory cytokines. This causes a strep toxic shock syndrome. Streptokinase: activates the proteolytic enzyme plasmin, which breaks up fibrin blood clots Hyaluronidase, DNAase, anti-5a peptidase, and others.

Where are enterococci found?

The enterococci take up residence in the human intestines and are considered normal bowel flora. They are variably hemolytic and unique in that they all grow well in *40% bile* or *6.5% NaCl*. Clinically, the enterococci are commonly the infecting agents in the urinary tract infections, biliary tract infections (as they grow well in bile), bacteremia, and subacute bacterial endocarditis. This bugs are always around the GI tract and prey on weak hospitalized patients. The enterococci are currently the second to third most common cause of hospital acquired infection. In hospitalized patients the enterococci frequently cause UTI, wound infections, and native and prosthetic valve endocarditis.

Where are strep pneumococci found?

The epidemiology includes the normal flora of the throat infecting a human endogenously or exogenously. The highest incidence of these infections are in the very young or the elderly due to the lack of antibodies.

What is the major virulence factor of strep pneumococcus?

The major virulence factor of the pneumococcus is its polysaccharide capsule, which protects the organism from being phagocytosized. The capsule is antigenic and antibodies specific for the capsule can neutralize the pneumococcus. The only problems is that there are 84 different capsule serotypes, so surviving an infection with this organism only provides immunity to 1 out of 83 capsule types. Vaccines produced in the very young or the elderly are based on these capsulated serotypes.

Lancefield antigens

The strep can also be classified based on the antigenic characteristics of the C carbohydrate ( a carbohydrate found on the cell wall). These antigens are called Lancefield antigens and are given letter names from A-S. This classification system was originally developed to differentiate beta-hemolytic strains of strep. However, there are so many different types of strep that we now rely less on the Lancefield antigens and more on a combination of tests. Although there are more than 30 species of strep, only 5 are significant human pathogens. Three of these pathogens have lancefield antigens: Group A, B, and D. The other two pathogenic species of strep genus do not have lancefield antigens, and are therefore called by their species name: Streptococcal Pneumoniae and Viridans group Strep.

Viridan group strep

There are also Viridans Streptococci. This is a heterogenous group and includes several species, such as S. salivarius, S. mitis, S. sanquis, and S. mutans. Can be alpha hemolytic or non-hemolytic and are associated with endocarditis

Group D strep

These bacteria, which can be alpha or gamma hemolytic, traditionally have been divided into two sub groups: Enterococci and non-enterococci.

Group B strep

These strep are also beta-hemolytic. When thinking of group B strep think of group B for BABY. About 25% of women carry these bugs vaginally, and a baby can acquire these bacteria during delivery. These organisms cause neonatal meningitis, pneumonia, and sepsis.

Viridans Group Strep

They are a heterogeneous collection of alpha and non-hemolytic strep. It is a constitute of main facultative oral flora. This is important in dental work, as one does not want these bacteria to get into the blood stream. These organisms can get attached to heart valves and damage them. They are involved in dental caries, but the plaque is not just this organism, but other anaerobic bacteria that have adhesins, allowing them to interact with one another. It can result in sub-acute bacterial endocarditis in patient with abnormal heart valves, dental caries, and intra-abdominal infections. This is a big, heterogenous group of strep that are not identified based on one lancefield group. Viridis is the latin word for green, and most of the viridans strep are alpha-hemolytic, producing greenish discoloration on blood agar. They are normal human GI tract flora that are frequently found in the nasopharynx and gingival crevices.

Acute post-strep glomerulonephritis

This is an antibody-mediated inflammatory diease of the glomeruli of the kidney. It occurs one week after infection of either the pharynx OR skin by nephritogenic strains of beta hemolytic strep group A. Only a few strains of beta hemolytic group A streptococci are nephritogenic. Certain antigens for these nephritogenic strep induce an antibody response. The resulting antigen-antibody complexes travel to and are deposited in the glomerular basement membrane, where they activate the complement cascade. This leads to local glomerular destruction in the kidney. Clinically, a child will show up to your office, and his mother with complain that his face is puffy. This is caused by the retention of fluid from his damaged kidney. His urine is darker than normal (tea of coke colored) due to hematuria. The child may also have hypervolemia secondary to fluid retention, which can cause high blood pressure. Upon further examination you may be able to elicit the fact that he had a sore throat or skin infection a week or so ago. This type of glomerular disease usually has a good prognosis.

Strep Pharyngitis

This is the classic strep throat with red swollen tonsils and pharynx, a purulent exudate on the tonsils, high temperature, and swollen lymph nodes. It usually lasts 5 days (penicillin therapy speeds recovery). Because exudative pharyngitis (pus on tonsils) can be caused by non-strep organisms like viruses a throat swab should be sent for a *rapid antigen detection test*. These tests can be completed in minutes and are highly specific for strep pyogenes and immunologically detect group A carbohydrate antigen. In children negative RADTs should be backed up by a throat culture due to the high incidence of strep throat in this population and only moderate sensitivity to the RADT.

How to treat enterococci infections

This organism is resistant to many commonly used antibiotics. It is treated by a synergistic combination antibiotic therapy, such as aminoglycoside and a cell wall active antibiotic.

Group A Beta hemolytic strep

aka Strep Pyogenes (which means pus-producing) and cause the diseases "strep throat", scarlet fever, rheumatic fever, and post-strep glomerulonephritis.

Scarlet fever

certain beta-hemolytic group A strep not only cause a sore throat, but also produce a exotoxin called either pyrogenic toxin or erythrogenic toxin. This exotoxin is acquired by lysogenic conversion. The exotoxin produces fever (so it is pyrogenic) and causes a scarlet red rash. The rash begins on the trunk and neck, and then spreads to the extremities, sparing the face. The skin may peel off in fine scales during healing.

Pyoderma

is a pustule, usually on the extremity or face, that breaks down after 4-6 days to form a thick crust. It heals slowly and leaves a depigmented area

Erypsipelas

is a strep infection of the superficial skin, the dermis only. It has a specific appearance: a raised, bright red rash with a sharp border that advances from the initial site of infection. Unlike celllulitis, erysipelas is only rarely caused by staph aureus.