Gram Positive Cocci

Question 1

Prevention of S. pyogenes infection

Answer 1

As of yet, there is no vaccine.

Question 2

Coagulase Test

Answer 2

Organism is mixed with a small amount of plasma. A positive result is indicated by coagulation of the plasma, indicating that the organism produces coagulase

Question 3

__% of people who are sick with Staph. aureus are sick with the strain they are colonized with.

Answer 3

80% of people who are sick with Staph. aureus are sick with the strain they are colonized with.

Question 4

Why is capsule particularly imporant for a foreign organism to survive in the bloodstream?

Answer 4

1. Complement is everywhere in the bloodstream
2. Evasion of spleen phagocytes

Question 5

Staphylococci

Answer 5

Arranged in clusters. Express catalase.

Question 6

Simple test for staphylococci

Answer 6

Add one drop of H₂O₂ and analyze for catalase activity (O₂ production appears as bubbling)

Question 7

Factors that may predispose to pneumonia

Answer 7

Aspiration that can occur with loss of consciousness, cigarette smoking, alcohol consumption, viral infections, or excess fluid in the lungs

Question 8

Hemolytic classification of streptococci

Answer 8

Question 9

Classification of Streptococci and Enterococci

Answer 9

Hemolytic pattern, Group-specific antigens (Lancefield serotype classification), biochemical or molecular tests (to determine species).

Question 10

Diseases caused by S. pyogenes

Answer 10

Question 11

MRSA

Answer 11

Methicillin-resistant Streptococcus Aureus

Increasingly common. Require treatment with vancomycin.

Question 12

Your patient comes in with symptoms of diarrhea and vomitting. He tells you that he recently had old meat which he thought may have gone bad, but said this couldn’t have been the cause since he cooked it thoroughly to be sure it was okay. What happened?

Answer 12

Cooking doesn’t do the job. Staphylococcal enterotoxins are heat stable, not all of them will be destroyed by cooking.

Question 13

Three major staphylococci species

Answer 13

Staphylococcus aureus (cat +, coag +)

Staphylococcus epidermidis (cat +, coag -)

Staphylococcus saprophyticus (cat +, coag -)

Question 14

Treatment of S. pneomoniae infection

Answer 14

The first line is vaccination. If infection does occur:

Penicillin and 3rd generation cephalosporins are usually effective, but resistance is growing. This resistance is β-lactamase independent, so β-lactamase inhibitors are no good. All S. pneumoniae are sensitive to vancomycin

Question 15

Staphylococci are arranged in ____

Answer 15

Staphylococci are arranged in clusters

Question 16

Staphylococcus saprophyticus almost exclusively cause ______

Answer 16

Staphylococcus saprophyticus almost exclusively cause urinary tract infections.

Question 17

Staphylococcus damage mechanism

Answer 17

• protein A, cell wall component that binds Fc region of IgG.
• Catalse counteracts killing by leukocyte-derived ROS
• Coagulases convert fibrinogen to fibrin, clotting to avoid phagocytosis
• More than 90% are encapsulated
• Secrete pore-forming toxins, including hemolysins and Panton-Valentine leukocidin, which kill neutrophils
• Most strains also make lipases, proteases, deoxyribonucleases

Question 18

Clinically significant streptococci

Answer 18

• Streptococcus pyogenes*
• Streptococcus pneumoniae*

Question 19

Most streptococci form ____ chains, with the exception of ____.

Answer 19

Most streptococci form long chains, with the exception of streptococcus pneumoniae.

Streptococcus pneumoniae is arranged as pairs or short chains.

Question 20

Transmission of S. pneumoniae

Answer 20

Respiratory droplets. Highly efficient. Thankfully it is usually quite innocuous

Question 21

Toxic shock syndrome symptoms and treatment

Answer 21

a sunburn-like rash (erythroderma), bright red eyes (conjunctivitis), vomiting and diarrhea, and significantly elevated creatinine (acute kidney failure)

Treat with clindamycin and IVIG

Question 22

Why is it particularly important to give antibiotics for strep throat, even if it is not a particularly severe case?

Answer 22

Antibiotics significantly reduce the risk of acute rheumatic fever 1-4 weeks post-infection. Unfortunately, this does not reduce the risk of acute poststreptococcal glomerulonephritis.

Question 23

S. pyogenes-induced necrotizing fasciitis and myositis

Answer 23

1–3 per 100,000 in the United States, very rare

S. pyogenes reaches fascia between the skin and muscle. Enables rapid spread of S. pyogenes along this plane. Streptokinase enables cell to travel through clotts so it cannot be cut off, and its degrative enzymes and streptolysins S and O​ destroy whatever is in its path.

Question 24

Most common S. pneumoniae infection manifestations

Answer 24

Pneumonia

Meningitis

Otitis media (middle ear infection)

Sinusitis

Question 25

Answer 25

Staphylococcus

Question 26

*S. pyogenes*

Answer 26

Found in the nasopharynx and skin of ~20% school-aged children, lasting weeks or months at a time. Usually asymptomatic. Person-to-person spread by **respiratory droplets** or **skin-to-skin contact.**

Question 27

Diagnosis of S. pneumoniae infection

Answer 27

Pneumococcal infection is often suspected for pneumonia. **Sputum** (pneumonia) or **CSF** (meningitis) must first be obtained. If Gram stain yields **neutrophils** and **abundant lancet-shaped** (oval) **Gram-positive diplococci**, then *S. pneuoniae* is likely. **Culture** may be performed to confirm. **For CSF, PCR may be performed.**

Question 28

Based on symptoms alone, streptococcal pharyngitis cannot be reliably distinguished from \_\_\_\_.

Answer 28

Based on symptoms alone, streptococcal pharyngitis cannot be reliably distinguished from **viral pharyngitis**

Question 29

Mechanisms that typically prevent lung infection

Answer 29

The **tortuous pathway** that air and inhaled particles must follow to reach the lungs, the **epiglottis** that protects the airway from aspiration, the **cough reflex**, the **mucociliary escalator**, and **alveolar macrophages** that phagocytose bacteria and foreign particles, mucus **IgA**, the **mucosal associated lymphoid tissues** that provide adaptive immune defense.

Question 30

Prevention of S. pneumoniae infection

Answer 30

Occurence of S. pneumoniae-induced pneumonia and meningitis have both decreased due to the success of the **S. pneumoniae vaccines**. **Conjugate vaccine**: protects against **13 of the most common childhood disease-associated capsular serotypes.** Intended to prevent meningitis in children. **Polysaccharide vaccine**: **Capsule from 23 common disease causing capsular serotypes**. Intended to prevent pneumonia and recommended for older adults at specific risk for infection.

Question 31

Prevention of Streptococcus aureus infection

Answer 31

Currently, there is no S. aureus vaccine, and attempts to develop vaccines are ongoing

Question 32

Streptococcal pharyngitis

Answer 32

**strep throat** **Acute (rapid) onset of sore throat**, **headache** and **fever** in a school-age child. There **swollen, tender cervical lymph nodes**, and the **oropharynx is often red** with a **grayish-white exudate** on the tonsils. Risk of **acute rheumatic fever** if not treated.

Question 33

Diagnosis of staphylococcus infection

Answer 33

Specimens from the site of infection should be collected for **Gram-stain and culture.**

Question 34

Gram Positive Cocci are separated into two major groups, ____ and \_\_\_\_, based on the arrangement of the cocci.

Answer 34

Gram Positive Cocci are separated into two major groups, **staphylococci** and **streptococci**, based on the arrangement of the cocci.

Question 35

Really the **only** important virulence factor of S. pneumoniae

Answer 35

The capsule!! Particularly immunongenic. Non-capsular S. pneumoniae is not virulent

Question 36

Staphylococcal scalded skin syndrome

Answer 36

Mediated by **exfoliative toxins A and B** (**serine proteases** that cause separation of the layers of the epidermis at the **desmosomes**). Life-threatening. Mainly affects **neonates**. Characterized by **extensive sloughing of the skin**.

Question 37

Rapid strep tests

Answer 37

Performed to differentiate a pharyngitis of streptococcal origin from one of viral origin. **Throat swab** and then culture the organism on blood agar plates to **assay for hemoylsins**. **Very specific**, so a positive test immediately diagnostic for *S. pyogenes*, however **not entirely sensitive**, so a negative does not rule *S. pyogenes* out.

Question 38

Source of Staphylococcus infection

Answer 38

Colonizes the nostrils in 30% of individuals. Over 90% of people are colonized at some point in their life. **Spreads by contact of fomites.** Infections are **opportunistic** and **usually occur** when one **contracts the S. aureus from another individual's microbiota.**

Question 39

Resistance to ______ has never been detected in GAS

Answer 39

Resistance to **penicillin** has never been detected in GAS. Thank god. This makes **penicillin** the absolute 100% safest go-to treatment for nonallergic patients. **For individuals allergic to penicillin**, **macrolide antibiotics** are appropriate; however, **erythromycin-resistant GAS have been found**.

Question 40

*S. pyogenes* usually remains localized to \_\_\_\_\_.

Answer 40

*S. pyogenes* usually remains localized to **the area of initial infection**. As it **cannot penetrate intact skin**.

Question 41

Acute poststreptococcal glomerulonephritis

Answer 41

Occurs 1-4 weeks after infection. May follow either a pharyngitis or skin/soft tissue infection. **Treatment with antibiotics does not affect the occurrence** of this complication. **Immune complexes** of streptococcal proteins and antibodies are deposited in the **glomerular basement membrane** and lead to **complement fixation with subsequent renal injury**. Have **blood and elevated protein in their urine,** and they may go on to **renal failure** and require **dialysis**.

Question 42

M protein

Answer 42

Question 43

Staphylococcus aureus-mediated disease

Answer 43

**Pyogenic (pus-forming) infections**: Most lead to **abscess formation** (pus pockets). Can spread to subcutaneous or submucosal tissue and cause diffuse tissue inflammation (**"cellulitis"**). May infect **nearly any site in body**: skin, lungs, heart, bone, etc, etc. **Exotoxin infections**: Many S. aureus secrete exotoxins that cause symptoms at sites distant to infection. May cause **Toxic shock syndrome, staphylococcal scalded skin syndrome,** or **staphylococcal food poisoning.**

Question 44

Answer 44

*Streptococcus pneumoniae*

Question 45

In addition to hemolysins and Panton-Valentine leukocidin preventing neutrophil-mediated clearance, they also. . .

Answer 45

. . .cause release of neutrophil granule contents, including lysosomal enzymes, into the tissue. This may act as another mechanism of damaging the area of infection, or areas distant which are reached by the toxins.

Question 46

Development of an abscess

Answer 46

Complicated process involving both host and bacterial participation. Starts as acute inflammatory reaction.

Question 47

*Staphylococcus aureus*

Answer 47

Gram +, Catalase +, Coagulase +, clustering cocci. **Colonies appear golden**, hence aureus. Most virulent and clinically significant member of Staphylococcus genus. Identified via coagulase test.

Question 48

How *S. pyogenes* adheres to the host nasopharynx

Answer 48

Uses **adhesins** and its **hyaluronic acid (HA) capsule**. The **HA capsule** **binds to CD44** (a homing cell adhesion molecule that participates in leukocyte rolling) found on the surface of pharyngeal epithelial cells and skin keratinocytes.

Question 49

*Streptococcus pneumoniae*-mediated damage

Answer 49

* **pneumolysin** (an exotoxin, **attacks membranes of host cells**, damaging tissue and killing phagocytes, **activates complement at distant sites** to deplete total serum complement and inflammatory cells) * **polysaccharide capsule** (the **primary virulence factor** for *S. pneumoniae*)

Question 50

Treatment of staphylococcus infection

Answer 50

**β-lactams**, **glycopeptides** (vancomycin), **antifolates**, protein synthesis inhibitors (**lincosamides, macrolides, aminoglycosides**). Usually responds well to smei-synthetic penicillins, like methicillin or the cephalosporines.

Question 51

S. pneumoniae is the most common cause of \_\_\_\_\_

Answer 51

S. pneumoniae is the most common cause of **community acquired pneumonia** (although many other organisms also cause this infection) **_AND_ bacterial meningitis** (especially in adults, but also in children)

Question 52

Streptococci (and the similar enterococci) are arranged in \_\_\_\_\_

Answer 52

Streptococci (and the similar enterococci) are arranged in **chains**

Question 53

Many streptococcal species cannot be assigned to any serotype group because \_\_\_\_.

Answer 53

Many streptococcal species cannot be assigned to any serotype group because **there are no antisera that react to their cell wall antigens**

Question 54

Answer 54

Streptococcus

Question 55

In a case of acute rheumatic fever and acute poststreptococcal glomerulonephritis, diagnosis requires evidence of \_\_\_\_\_\_.

Answer 55

In a case of acute rheumatic fever and acute poststreptococcal glomerulonephritis, diagnosis requires evidence of **a preceding *S. pyogenes* infection** Because the organisms may no longer be present, **antibodies to GAS antigens** can be used to establish a previous infection. The most common are the **antistreptolysin O titer, antiDNase B titer, and Streptozyme® screen**

Question 56

*S. pyogenes-*mediated damage

Answer 56

* **Adhesins** * **hyaluronic acid capsule** (binds **CD44** _and_ **mimicks human ECM,** effectively camoflouging the bacterium as matrix and preventing phagocytosis) * **M protein** (binds fibrinogen, aiding adhesion and preventing alternative complement activation and phagocytosis) * Induces a **very strong inflammatory repsonse**, forming **immune complexes** * Expresses several proteases, DNAses, and hyaluronidase * **Streptokinase** (converts **plasminogen to plasmin**, enabeling **travel through fibrin clots**) * **streptolysins S and O** (hemolysins that lyse the membranes of various host cells)

Question 57

Lancefield group A streptococci

Answer 57

*S. pyogenes*

Question 58

Acute rheumatic fever

Answer 58

A significant cause of **valvular heart disease** in the preantibiotic era and continues to be in low-income and lowermiddle income countries. Preceded 1-4 weeks by pharyngitis. **Damage to heart valves persists** even if acute inflammation ceases. May lead to **scarring and valve stenosis**. Turbulent valve flow also predisposes to future infections. Possibly a result of **cross-reactivity** between similar proteins in *S. pyogenes* and tissues in the heart, synovium, and brian.

Question 59

Toxic shock syndrome

Answer 59

Mediated by **toxic shock syndrome toxin-1** and **staphylococcal enterotoxins serotypes B and C.** All are **superantigens** which **cross-link one chain (β-chain)** of the **TCR** with **Class II MHC** on macrophages. This causes massive and nonspecific cytokine release, thus inducing TNF-α-mediated shock.

Question 60

The reservoir of *S. pneumoniae* is \_\_\_\_\_\_\_

Answer 60

The reservoir of *S. pneumoniae* is **humans colonized by the organism** It usually exists as a commensal organism.

Question 61

Staphylococcal food poisoning

Answer 61

Staphylococcal **enterotoxin serotypes A through E and I cause food poisoning** (think vowels). They **cause intensive intestinal peristalsis**, apparently by working directly on the **vomiting control center of the brain**. They are **heat stable, resist proteases**, and are not **necessarily destroyed by cooking**