S1B5 - Streptococcus

Question 1

How is S. pyogenes transmitted?

Answer 1

S. pyogenes is transmitted human-to human via respiratory droplets, food, or direct inoculation to the skin

Question 2

What are abnormal lab results of the cerebrospinal fluid of Streptococcus pneumoniae meningitis?

Answer 2

Lab results of S. pneumoniae meningitis are:

• bacteria in cerebrospinal fluid (CSF),
• elevated CSF protein,
• elevated PMNs, and
• low CSF glucose.

Question 3

Two weeks after having a sore throat and fever, a seven-year-old boy complains of knee pain, elbow pain, and chest pain. Physical examination demonstrates a macular rash on his trunk. What bacterial factor is involved in this disease?

A) Lipopolysaccharide

B) Polysaccharide capsule

C) SpeC

D) SpeA

E) M-protein

Answer 3

M-protein

Answer Explanation

Rheumatic fever is mediated by antibodies against S. pyogenes’ M-protein, making it an autoimmune disease. The major JONES criteria for diagnosis of rheumatic fever are carditis, polyarthritis, chorea, erythema marginatum, and subcutaneous nodules. Carditis can present as pericarditis, which would cause chest pain. The polyarthritis can occur in up to 80% of patients and most commonly involves multiple large joints. The rash and subcutaneous nodules are rare findings, and Sydenham’s chorea occurs late in rheumatic fever.

Question 4

What are some virulence factors that S. pneumoniae uses to evade the host immune system?

Answer 4

Streptococcus pneumoniae virulence factors are IgA protease and polysaccharide capsule (anti-phagocytic).

Question 5

An elderly patient is admitted from home with a pneumonia that is productive of rusty-colored sputum. Sputum cultures grow optochin-sensitive gram-positive bacteria. Which of the following diseases is least associated with this pathogen?

A) Meningitis

B) Endocarditis

C) Sinusitis

D) Otitis media

Answer 5

Endocarditis

Answer Explanation

Rusty-colored sputum is classic for S. pneumoniae, especially in the setting of community-acquired pneumonia. The culture results and optochin-sensitivity make it a firm diagnosis. In addition to CAP, S. pneumoniae is also the most common bacterial cause of meningitis, otitis media, and sinusitis. Endocarditis is associated with S. viridans.

Question 6

Does strep viridans have a capsule? How does this compare to strep pyogenes?

Answer 6

S. viridans has no capsule (differentiate from hyaluronic acid capsule of S. pyogenes, polysaccharide capsule of S. pneumoniae).

Question 7

Which streptococcal species causes dental caries?

A) Streptococcus pyogenes

B) Streptococcus pneumoniae

C) Streptococcus mutans

D) Streptococcus sanguis

Answer 7

S. mutans causes dental caries

Question 8

Describe the hemolytic pattern of Streptococcus gallolyticus (formerly Streptococcus bovis) on blood agar.

Answer 8

In the laboratory, Streptococcus gallolyticus grows on blood agar in small colonies that are typically non-hemolytic (variable presentation).

Question 9

A bacterial organism is found to be pyrrolidonyl arylamidase (PYR) test positive, what two organisms are high on your differential?

Answer 9

S. pyogenes is pyrrolidonyl arylamidase (PYR) test positive, a rapid test used for the presumptive identification of S. pyogenes and Enterococci.

Question 10

A 12-year-old girl is brought in by her mother, who reports dark brown urine and swelling around the daughter’s eyes. The patient may have complained about a sore throat 2 weeks prior. Which lab result would confirm the suspected diagnosis?

A) Serum negative for presence of anti-DNAse B antibodies

B) Urinalysis positive for protein and red blood cells

C) Serum BUN > 50

D) Elevated serum C3 concentration

E) Serum ASO titer > 1:330

Answer 10

Serum ASO titer > 1:330

Answer Explanation

The suspected diagnosis is post-streptococcal glomerulonephritis. The dark brown urine suggests hematuria, and the periorbital edema suggests loss of protein. The history of pharyngitis and patient age point toward streptococcal cause, rather than one of the many other causes of hematuria and proteinuria.

In the setting of a recent Group A strep infection, ASO titers (> 1:330), anti-DNAse B antibodies, and anti-hyaluronidase antibodies are frequently elevated. While UA will definitely show proteinuria and red cells, this confirms glomerulonephritis but not the specific entity. Serum C3 concentrations are usually decreased in the setting of PSGN.

Question 11

What is the morphology, gram staining, anaerobe/aerobe, and hemolysis on blood agar of Streptococcus pyogenes?

Answer 11

Streptococcus pyogenes (Group A Strep, GAS) is a facultative anaerobic, β-hemolytic, gram-positive cocci.

Question 12

What are the two species of Enterococci normally found in humans? Which is more common and which is more likely to be resistant to vancomycin?

Answer 12

E. faecalis is more common and less likely to be resistant to vancomycin, while E. faeciuM is less common and More likely to be vancomycin resistant (VRE).

Question 13

Is S. pyogenes bacitracin sensitive or resistant?

Answer 13

S. pyogenes is bacitracin sensitive, vs. S. agalactiae which is bacitracin resistant.

Question 14

What are some specific species within the Streptococcus viridans group of bacteria, and what diseases do they cause?

Answer 14

Streptococcus viridans is a large group of commensal (non-pathogenic) gram-positive bacteria:

• S. mutans causes dental caries;
• S. sanguinis is the most common cause of subacute endocarditis;
• S. mitis can also cause bacterial endocarditis.

Question 15

In what setting would you expect an Enterococci species infection?

Answer 15

Enterococci species are one of the leading causes of nosocomial infections in the U.S. due to high resistance.

Question 16

S. pyogenes infection from what body tissue often precedes rheumatic fever?

Answer 16

Note that rheumatic fever is generally preceded by GAS tonsillopharyngitis and NOT GAS skin infections (impetigo).

Question 17

How does S. pyogenes toxic shock-like syndrome differ from S. aureus toxic shock syndrome?

Answer 17

In toxic shock-like syndrome (TSLS) a systemic release of exotoxin A (SpeA) from a S. pyogenes skin infection (cellulitis) can cause polyclonal activation of T cells, leading to acute fever, shock, and multi-organ failure. In addition, TSLS patients from S. pyogenes infection present with painful, pre-existing skin infections and positive blood cultures.

S. aureus toxic shock syndrome (TSS) patients do not present with painful, pre-existing skin infections or positive blood cultures.

Question 18

What are 3 organisms that contain IgA protease?

Answer 18

Other organisms that contain IgA protease can be remembered by the mnemonic SHiN

• S. pneumoniae
• H. influenzae type B
• Neisseria

Question 19

What patients should receive the pneumococcal conjugate vaccine (a.k.a Prevnar)?

Answer 19

The pneumococcal conjugate vaccine (Prevnar) is given to children under 5 years and adults over 65 to prevent Streptococcus pneumoniae infection.

Question 20

What types of surfaces does Streptococcus gallolyticus prefer to infect once in the bloodstream?

Answer 20

From the blood stream, the organism prefers to attach to collagen-rich surfaces (such as valvular surfaces) via pilus-like structures.

Question 21

Which virulence factor allows S. pneumoniae to colonize the nares?

A) Beta-hemolytic activity

B) Polysaccharide capsule

C) TSST-1 superantigen

D) IgA protease

E) Alpha-hemolytic activity

Answer 21

IgA protease

Answer Explanation

Mucosal surfaces are usually covered with IgA as a means of passive immunity. S. pneumoniae can produce IgA protease, allowing it to colonize the nares. Its polysaccharide capsule is a virulence factor that inhibits C3b opsonization. While S. pneumoniae does have alpha-hemolytic activity, this is not in itself a virulence factor. Beta-hemolytic activity is a marker of Group B streptococcus. TSST-1 superantigen is secreted by S. aureus and causes toxic shock syndrome.

Question 22

How does local infection with Enterococci species normally occur?

Answer 22

Infection may occur when Enterococci species overgrows locally when antibiotics suppress normal flora.

Question 23

What factors increase the risk of contracting S. pneumoniae in a patient?

Answer 23

Patients at a higher risk for contracting pneumonia include those with

• Asthma
• Viral infection
• Smoking history
• Asplenic
• Immunocompromised

Question 24

Name three disease entities caused by Enterococci infections.

Answer 24

Patients typical present with UTIs or biliary tract infections if infection is local. Systemic infections usually manifest as subacute bacterial endocarditis (SBE).

Question 25

Colonization of heart valves by *Enterococci* species happens after being previously affected with what disease?

Answer 25

In SBE, enterococci, as well as *S. viridans*, **colonize heart valves previously damaged from rheumatic fever.**

Question 26

If a patient presents with *Streptococcus gallolyticus* bacteremia, what other diagnostic evaluations should be performed?

Answer 26

Patients with *Streptococcus gallolyticus* bacteremia should be investigated for **colorectal neoplasms (colonoscopy)** due to strong correlation.

Question 27

What is required to make a diagnosis of rheumatic fever?

Answer 27

Diagnosis of rheumatic fever requires **evidence of a recent GAS infection** (serology from Antistreptolysin O titer or anti-DNase B titer or bacterial culture) and either **two major OR one major and two minor Jones criteria.**

Question 28

What are the three most common causes of neonatal meningitis from 0-6 months?

Answer 28

The three most common causes of neonatal meningitis from 0-6 months is: * ***S. agalactiae*** (group B) * ***E. coli*** * ***Listeria***

Question 29

What factors make an individual high-risk for a severe *Streptococcus pneumoniae* infection?

Answer 29

**Immunocompromised, asplenic, and older patients** are at higher risk for a more severe infection.

Question 30

Is *S. agalactiae* bacitracin resistant or sensitive?

Answer 30

*S. agalactiae* is **bacitracin resistant**. Contrast this with *S. pyogenes*, which is bacitracin sensitive. (Bacitracin is A in the picture)

Question 31

What should be administered to pregnant women who test positive for *Streptococcus agalactiae?*

Answer 31

Pregnant women with positive cultures receive **intrapartum penicillin prophylaxis.**

Question 32

A 19-year-old woman presents in severe shock. Which finding would favor *Streptococcus pyogenes* over *Staphylococcus aureus* as the source of her shock? A) Lobar pneumonia on chest X-ray B) A borad-based, tender cellulitis on her thorax C) A migratory polyarthritis with associated pericardial fluid collection D) A tampon left in place for 2 weeks E) A chronic wound on her leg with exposed bone

Answer 32

A broad-based, tender cellulitis on her thorax Answer Explanation Both *S. pyogenes* and *Staphylococcus aureus* can cause toxic shock, a superantigen toxin–mediated disease. The classic finding in S. aureus–caused toxic shock syndrome is a retained tampon. In S. pyogenes, the shock is preceded by a very tender soft tissue infection, such as necrotizing fasciitis. Chronically exposed bone is by definition osteomyelitis, but this only rarely presents as systemic disease. Lobar pneumonia can result in bacteremia, and proceed to shock, but GAS is not associated with pneumonia. Migratory polyarthritis and carditis are two of the JONES criteria for rheumatic fever, a late sequela of strep throat, but again is not associated with shock.

Question 33

“Rusty” sputum is classically associated with pneumonia caused by what pathogen?

Answer 33

Patients with ***Streptococcus pneumoniae*** will have red or brown sputum, classically described as “**rusty**.” Bacteremia may follow.

Question 34

*Streptococcus gallolyticus*, formerly known as *Streptococcus bovis*, infections has a high correlation with what other diseases besides endocarditis?

Answer 34

*Streptococcus gallolyticus* infections are known to cause **infective endocarditis** and have an extremely high correlation with **colorectal neoplasms**. Other sites of infection include the urinary and biliary system.

Question 35

What are the effects of streptolysin O and S in *S. pyogenes*?

Answer 35

*S. pyogenes* also synthesizes streptolysin O and streptolysin S, which **destroys red and white blood cells.**

Question 36

A patient with a 3-month-long stay in the intensive care unit is treated for a urinary tract infection. Urine cultures grow gram-positive cocci in pairs with variable hemolysis. What is the likely pathogen? A) *Escherichia coli* B) *Staphylococcus aureus* C) *Corynebacterium* D) *Enterococcus* E) *Proteus mirabilus*

Answer 36

*Enterococcus* Answer Explanation The description of the laboratory findings, a gram-positive cocci with variable hemolysis, from a nosocomial urinary tract infection a gram-positive cocci with variable hemolysis is diagnostic for enterococcus.

Question 37

A systemic release of exotoxins A, B, and C from S. pyogenes causes what disease?

Answer 37

Systemic release of exotoxins A, B, and C, the superantigens, causes **scarlet fever.**

Question 38

Which different infections are commonly caused by *Streptococcus pneumoniae*?

Answer 38

S. pneumoniae causes **C-MOPS** * **C**onjunctivitis, with patients presenting with redness and discharge in one eye * **M**eningitis, with patients presenting with fever, chills, headache and neck stiffness * **O**titis media, with patients presenting with ear pain * **P**neumonia (community-acquired lobar), with patients presenting with fever, chills, cough, and chest pain * **S**inusitis, with patients presenting with fever, purulent nasal discharge, and sinus tenderness

Question 39

How is *Streptococcus gallolyticus*, formerly known as *Streptococcus bovis*, able to escape immune detection in the GI tract in order to reach systemic infection?

Answer 39

*Streptococcus gallolyticus* enters humans via the lower gastrointestinal tract or oropharynx. The **organism escapes immune detection using encapsulation while in the lamina propria** which then allows it to penetrate the blood stream causing bacteremia.

Question 40

How does non-bullous impetigo present? What is the most likely causative organism, *S. aureus* or *S. pyogenes*?

Answer 40

Patients with skin infections from *S. pyogenes* may present with **pustular lesions and honeycomb-like crusts** known as **non-bullous impetigo** at the site of inoculation. S. aureus, however, is the most common cause of both non-bullous and bullous impetigo.

Question 41

What are the treatment options for non-resistant species of *Enterococci*? For resistant species?

Answer 41

Treatment includes ampicillin or **vancomycin/aminoglycosides (synergistic)** for non-resistant species. For VRE, treatment includes **linezolid and streptogramins (quinupristin and dalfopristin).**

Question 42

What role does streptokinase play in the virulence of *S. pyogenes*?

Answer 42

*S. pyogenes* contains streptokinase, an enzyme that **converts plasminogen to plasmin and results in fibrinolysis.** Surface bound plasmin activity promotes systemic spread of bacterial cells through degradation of tissue barriers and through modulation of the host immune response.

Question 43

What are the 2 components of the antigen in the *S. pneumoniae* vaccine given to infants and toddlers? Why are both 2 components required in this population?

Answer 43

The antigen in the *S. pneumoniae* vaccine (PCV13) given to infants and toddlers is composed of a **polysaccharide capsule + protein conjugate** that is similar to diphtheria toxin. The protein conjugate is required because **polysaccharide antigens alone are poorly antigenic in infants and toddlers.**

Question 44

What disease is exotoxin B (SpeB) of *S. pyogenes* associated with?

Answer 44

**Exotoxin B (SpeB)** is a protease precursor that becomes activated to a cysteine protease. SpeB is associated with **necrotizing fasciitis.**

Question 45

5-10% of adults have *S. pneumoniae* colonization of their nares. How does this organism avoid immunoglobulins present in mucus?

Answer 45

IgA protease **cleaves secretory IgA** (present in mucus). 5-10% of adults have nares colonized with pneumococcus.

Question 46

How does hyaluronidase contribute to the virulence of *S. pyogenes?*

Answer 46

*S. pyogenes* contains **hyaluronidase** that breaks down connective tissue, facilitating spread through tissues (cellulitis).

Question 47

Which bacteria commonly colonizes the female vaginal tract and often causes neonatal meningitis?

Answer 47

*S. agalactiae* causes **neonatal meningitis, pneumonia, and sepsis.**

Question 48

In diagnosing rheumatic fever, what are the major and minor JONES criteria?

Answer 48

Major JONES criteria include * **J**oints that are affected with migratory polyarthritis * **O** or carditis (think of “O” as ♥), which may include endocarditis, myocarditis, or pericarditis * **N**odules (subcutaneous) on extensor surfaces (e.g. wrist, elbow, knee) * **E**rythema marginatum rash, which is described as the presence of pink rings involving the trunk and sometimes the limbs * **S**ydenham chorea, a neurologic disorder consisting of abrupt, nonrhythmic involuntary movements, muscular weakness, and emotional disturbances Minor Jones criteria include * **Fever** * **Arthralgia** (cannot be used as criteria if polyarthritis is evident) * **Increased serum levels of acute phase reactants** (e.g. CRP, ESR) * **Prolonged PR interval** on EKG

Question 49

Is *Streptococcus gallolyticus* (formally *Streptococcus bovis*) able to grow in 6.5% NaCl?

Answer 49

*Streptococcus gallolyticus* is **inhibited by 6.5% NaCl** and expresses Lancefield group D antigen. Compare with group D enterococci like *Enterococcus faecalis*, which can grow in 6.5% NaCl.

Question 50

Is *S. viridans* alpha or beta hemolytic?

Answer 50

*S. viridans* alpha-hemolytic (like *S. pneumoniae*), in contrast to β-hemolytic *S. pyogenes* and *S. agalactiae.*

Question 51

Which feature distinguishes *Streptococcus pneumoniae* from viridans streptococci? A) S. pneumoniae grows next to optochin discs, viridans streptococci does not B) S. pneumoniae grows on plood agar, viridans streptococci does not C) S. pneumoniae is insoluble in bile, viridans streptococci is soluble D) S. pneumoniae does not grow next to optochin discs, viridans streptococci does grow next to optochin discs

Answer 51

*S. pneumoniae* does not grow next to optochin discs, *viridans streptococci* does grow next to optochin discs. Answer Explanation *Streptococcus pneumoniae* and *viridans streptococci* are both gram-positive cocci that grow in chains. *S. pneumoniae* is optochin-sensitive, so it will not grow immediately next to optochin-impregnated discs. *Viridans streptococci* is optochin-insensitive, so it will grow next to optochin. Both organisms will grow on blood agar. *S. pneumoniae* is bile soluble, while Viridans streptococci is bile insoluble.

Question 52

What is the gram stain of *Streptococcus gallolyticus*, formerly known as *Streptococcus bovis*? Is it catalase negative or positive?

Answer 52

*Streptococcus gallolyticus* (formerly *S. bovis*) is **catalase-negative, gram-positive coccus** that is considered a member of Group D Streptococcus (GDS). This species is not part of the normal flora.

Question 53

What virulence factor of *Streptococcus pneumoniae* puts asplenic patients particularly at risk of septic infection?

Answer 53

The **capsule** of *Streptococcus pneumonia* makes asplenic patients (e.g. sickle cell & splenectomy pts) particularly at risk for sepsis. Prophylactic vaccination of these patients is considered standard of care.

Question 54

What is the difference between erysipelas and cellulitis?

Answer 54

Erysipelas is a **superficial** *S. pyogenes* infection of the skin. Cellulitis is a **deeper process** that extends to the subcutis. Both are red, tender, and warm, however *cellulitis has ill-defined borders.*

Question 55

What type of hemolysis does *Streptococcus pneumoniae* exhibit on blood agar? Quellung test positive or negative? Optochin sensitive or resistant? Catalase negative or positive?

Answer 55

On blood agar, they are **alpha-hemolytic, catalase negative** and **optochin-susceptible**. They can be detected with the **positive quellung reaction**.

Question 56

Which of the following organisms is hippurate positive? A) *C. trachomatis* B) S. agalactiae C) *B. anthracis* D) *S. aureus*

Answer 56

*S. agalactiae* Answer Explanation Hippurate Test is to be used in the presumptive identification of *Gardnerella vaginalis, Campylobacter jejuni, Listeria monocytogenes* and group B streptococci, by detecting the ability of the organism to hydrolyze hippurate.

Question 57

What causes the post-streptococcal glomerulonephritis seen in patients with a recent skin and pharyngeal streptococcal infections?

Answer 57

Post-streptococcal glomerulonephritis follows skin or pharyngeal streptococcal infections. **Circulating immune complex deposition causes glomerular damage** and subsequent nephritic syndrome.

Question 58

What is the most common overall bacterial cause of sore throat?

Answer 58

*S. pyogenes* is the most common bacterial cause of sore throat. Patients may present with **fever, malaise, sore throat or enlarged cervical lymph nodes.**

Question 59

How is *Streptococcus pneumoniae* transmitted?

Answer 59

*S. pneumoniae* is transmitted via **respiratory droplets** and often occurs in people predisposed to pneumonia, ear infection, and meningitis.

Question 60

Where can *S. pyogenes* normally be found?

Answer 60

*S. pyogenes* is **part of the normal flora** of skin and the oropharynx.

Question 61

What tests can be done to help diagnose post-streptococcal glomerulonephritis?

Answer 61

Diagnosis of post-streptococcal glomerulonephritis can be made with **elevated titers of antistreptolysin O (ASO)** or **anti-DNase B.**

Question 62

How would *Streptococcus pneumoniae* otitis media be diagnosed?

Answer 62

Lab results of *S. pneumoniae* otitis media are fluid in middle ear behind tympanic membrane and bacteria in this fluid. However, usually clinical diagnosis is sufficient enough to progress towards treatment.

Question 63

Where is *S. agalactiae* normally found?

Answer 63

*S. agalactiae* is **part of the natural flora of the gastrointestinal and vagina.**

Question 64

Release of which bacterial toxin results in toxic shock-like syndrome?

Answer 64

**Exotoxin A (SpeA)** results in **toxic shock like syndrome**

Question 65

What types of treatments are given for patients infected with *Streptococcus gallolyticus*?

Answer 65

*Streptococcus gallolyticus* infections can be treated with **penicillin G**, but the species is also susceptible to **vancomycin** and **later generation cephalosporins**.

Question 66

Is *Streptococcus viridans* optochin-resistant or optochin-sensitive?

Answer 66

*S. viridans* is **optochin resistant** (differentiate from optochin-sensitive *S. pneumoniae*). (optochin = P disk)

Question 67

What is the mechanism underlying rheumatic fever?

Answer 67

Rheumatic fever is caused by a **cross-reactivity between *S. pyogenes* antigens (esp. M. proteins) and self-antigens.** 80% of cases are in children and present 2-3 weeks post-infection.

Question 68

How does the hyaluronic acid capsule contribute to the virulence in *S. pyogenes?*

Answer 68

*S. pyogenes* contains a hyaluronic acid capsule that gives it **antiphagocytic properties.**

Question 69

Where are *Enterococci* species normally found?

Answer 69

*Enterococci* species **normally inhabit intestines, biliary tract,** and **genitourinary tract**.

Question 70

What is the morphology, gram staining, catalase positive/negative, and hemolysis on blood agar of *Streptococcus agalactiae*?

Answer 70

Streptococcus agalactiae (GBS, Group B streptococcus) is a **catalase negative gram-positive cocci with beta hemolysis on blood agar.**

Question 71

What is the antibiotic used for *S. agalactiae* infections?

Answer 71

Treatment includes **penicillin G.** Pregnant women with positive cultures receive **intrapartum penicillin prophylaxis.**

Question 72

How does systemic infection with *Enterococci* species normally occur? Where does it often colonize?

Answer 72

Systemic infection occurs when bacteria enter bloodstream **when mucosal or epithelial barrier is disrupted** and **often colonize heart valves**.

Question 73

Lancet-shaped, gram-positive bacteria are isolated from the CSF of a patient with meningitis. Which patient population is at risk for infection by this pathogen? A) Adult patient with sickle cell disease B) Patients who only received the heptavalent conjugate vaccine C) Patients who only receive the 23-valent conjugate vaccine D) Patients with nares colonized by this bacterium E) Patients with intracranial hemorrhage

Answer 73

Adult patients with sickle cell disease Answer Explanation The question stem describes ***S. pneumoniae***, which causes meningitis, otitis media, sinusitis, and community-acquired pneumonia. The polysaccharide capsule inhibits opsonization, and **patients missing spleens** (e.g. sickle cell patients or splenectomized patients) **are more at risk** for infection. Patients who received either the 7- or 23-valent vaccine are less at risk for infection. Colonization of nares doesn’t increase risk for meningitis, nor does intracranial bleeding.

Question 74

What are manifestations of scarlet fever?

Answer 74

In scarlet fever there is a systemic release of pyrogenic exotoxins A, B, and C (SpeA, SpeB, and SpeC). This leads to: * Fever * Pharyngitis (sore throat) * **“Strawberry” tongue** (may also be seen in Kawasaki disease) * **Confluent erythematous sandpaper-like (fine, blanching) rash** that begins on the chest and neck and spreads outward. * **“Circumoral pallor,”** where a rash spares the nasolabial triangle and chin * **“Pastia lines,”** where there is an accentuation of rash in a linear pattern along skin folds * Rash may be followed by fine desquamation (peeling) starting with the fingers in the second week

Question 75

Are *Enterococci* species catalase negative or positive?

Answer 75

*Enterococci* species are **catalase negative**.

Question 76

Which organism is not bile soluble, *Streptococcus viridans* or *Streptococcus pneumoniae*?

Answer 76

*S. viridans* is **not bile soluble**, i.e. not susceptible to lysis by bile (vs. *Streptococcus pneumoniae*, which is bile soluble).

Question 77

A patient is diagnosed with bacterial endocarditis and dextrans are found on the patient's damaged heart valves. What organism is most likely responsible?

Answer 77

*S. sanguinis* makes **dextrans** which bind to fibrin-platelet aggregates on damaged heart valves.

Question 78

What is the morphology, gram staining, anaerobe/aerobe, and hemolysis on blood agar of *Enterococci* species?

Answer 78

*Enterococci* species are **gram-positive facultative anaerobes that form short to medium length chains with variable hemolysis on blood agar.**

Question 79

Resistance to which of the following antibiotics is least likely to develop in *Enterococci*? A) Amikacin B) Oxacillin C) Gentamicin D) Daptomycin E) Vancomycin

Answer 79

Daptomycin Answer Explanation *Enterococcus* is notorious for **resistance to aminoglycosides** (amikacin, gentamicin) and vancomycin (VRE, or vancomycin-resistant enterococci). Enterococcus is also often resistant to oxacillin, in fact more often than it is resistant to penicillin. **Daptomycin resistance remains rare**.

Question 80

What role does M protein play in the virulence of *S. pyogenes?*

Answer 80

*S. pyogenes* contains M protein, the main virulence factor that **inhibits opsonization and phagocytosis by blocking complement**. There are 100+ immunotypes of M protein.

Question 81

What virulence factors secreted by *S. pyogenes* act as superantigens?

Answer 81

*S. pyogenes* synthesizes **exotoxins A, B, and C that are subject to lysogenic conversion** (also called Spes, scarlet fever toxins, and erythrogenic toxins) and act as **superantigens.**

Question 82

How do *Streptococcus pneumoniae* appear upon gram stain and microscopy?

Answer 82

Gram staining will show gram-positive *lancet-shaped* diplococci growing in chains.

Question 83

What specimens are taken to diagnose *Streptococcus pneumoniae* infections? What can be used to diagnosis otitis media?

Answer 83

Diagnosis is made with: * **sputum sample** for pneumonia, * **CSF sample** for meningitis, and * **visualization with an otoscope** for otitis media

Question 84

How is *Streptococcus pneumoniae* pneumonia treated?

Answer 84

Treatment for *S. pneumoniae* should include a **respiratory fluoroquinolone (levofloxacin or moxifloxacin)** or **combination therapy with a beta-lactam plus either a macrolide or doxycycline.**

Question 85

A 1-day old newborn develops sepsis. Blood cultures grow gram-positive cocci in chains that are resistant to bacitracin. The most likely risk factor for this infection is colonization of which of the following? A) Hospital bed B) Mother's breast ducts C) Newborn's central nervous system D) Newborn's gastrointestinal tract E) Mother's vagina

Answer 85

Mother’s vagina Answer Explanation Group-B strep classically causes perinatal pneumonia, meningitis, and sepsis. 25% of pregnant women have vaginal/rectal colonization, and the pathogen is passed to the neonate during birth.

Question 86

What autoimmune diseases are caused by *S. pyogenes?*

Answer 86

Autoimmune diseases caused by *S. pyogenes* include * **Rheumatic fever** (a Type II hypersensitivity reaction) * **Post-streptococcal glomerulonephritis** (a Type III hypersensitivity reaction) * **Pediatric autoimmune neuropsychiatric disorder** associated with group A streptococci (PANDAS) syndrome

Question 87

What special growth conditions can be used to differentiate *Enterococci* species from nonenterococci?

Answer 87

Enteroccoci species grows on **6.5% NaCl (vs. Nonenterococci) and 40% bile culture media.**

Question 88

What is the role of M protein in *Streptococcus pyogenes* infections? A) Inhibit opsonization B) Claeve antibodies C) Facilitate bacterial entry into cells D) Function as a superantigen

Answer 88

Inhibit opsonization Answer Explanation **M protein is the main virulence factor of *S. pyogenes*** that functions to **inhibit opsonization**. Facilitate bacterial entry into cells is incorrect because S. pyogenes is not an intracellular pathogen. Cleave antibodies refers to IgA protease, which S. pyogenes does not contain. SpeA and SpeC are exotoxins of the superantigen family that are secreted by S. pyogenes, not M protein.

Question 89

What are the important indications for pneumococcal polysaccharide vaccine (Pneumovax) immunization against *Streptococcus pneumoniae*?

Answer 89

**Immunocompromised** and **asplenic** patients, as well as **adults over 65** should be immunized with the *pneumococcal polysaccharide vaccine* (**Pneumovax**).

Question 90

What are the typical manifestations of pyogenic *S. pyogenes* infection (i.e. not autoimmune or toxin-related manifestations)?

Answer 90

Pyogenic infections caused by *S. pyogenes* include * **pharyngitis (“strep throat”),** * **non-bullous impetigo,** * **erysipelas/cellulitis.**

Question 91

What is the CAMP test? Which two microbes are CAMP positive?

Answer 91

*S. agalactiae*, along with *Listeria monocytogenes,* exhibits **a positive CAMP test** (CAMP factor enlarges the area of hemolysis formed by beta-hemolysin from *Staphylococcus aureus*).

Question 92

What lab tests can be used to detect recent infection with *strep pyogenes*?

Answer 92

Diagnosis of *S. pyogenes* pyogenic and toxin-mediated diseases can be made through **throat or skin culture**. Recent infections can be detected with **elevated titers of antistreptolysin O (ASO)** or **anti-DNase B.**