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Block 2 - Week 2 > Gram-positive cocci > Flashcards

Gram-positive cocci Flashcards

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1
Q

What test do we use to differentiate Staphylococci from Streptococci and Enterococci?

Which result indicates which bacteria?

A

Catalase Test

Catalse (+) = Staphylococci

Catalse (-) = Streptococci or Enterococci

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2
Q

What are some important catalase-positive organisms?

A
  • Staphylococci
  • Nocardia
  • Pseudomonas
  • Listeria
  • E. coli
  • Candida
  • Aspergillus
  • Serratia
  • B cepacia
  • H pylori
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3
Q

Once a bacteria is determined to be catalase (+), what is the next test you run to determine the bacteria species?

A

Coagulase Test

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4
Q

What test results would indicate that the bacteria is Staphylococcus aureus?

A

Catalase (+)

Coagulase (+)

Staphylococcus aureus also ferments mannitol (this test is not used often)

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5
Q

Hemolytic Activity Test

  • Alpha (a) shows: ?
    • Indicates bacteria: ?
  • Beta (B) shows: ?
    • Indicates bacteria: ?
  • Gammma (y) shows: ?
    • Indicates bacteria: ?
A

Hemolytic Activity Test

  • Alpha (a) shows: partial hemolysis. Green-ish color around colony due to release of peroxide
    • Indicates bacteria: Strep pneumoniae and Viridans Strep
  • Beta (B) shows: Total lysis of RBCs
    • Indicates bacteria: Strep pyogenes (Group A Strep) and Strep agalactiae (Group B Strep)
  • Gammma (y) shows: Zero hemolytic activity
    • Indicates bacteria: Enterococcus and Sterp bovis
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6
Q

Staphylococcus

Shape: ?

____ anaerobes

Color: ?

Species associated with disease: ?

A

Staphylococcus

Shape: groups of circles (looks like bunches of grapes)

Facultative anaerobes

Color: yellow

Species associated with disease:

  • S. aureus (Cat + and Coag +)
  • S. epidermidis (Cat +, Coag -, Novobiocin sensitive)
  • S. saprophyticus (Cat +. Coag -. Novobiocin resistant)
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7
Q

S. aureus virulence factors that inhibit phagocytosis (2 examples)

A

S. aureus virulence factors that inhibit phagocytosis

  • Coagulase = clumping factor: binds fibrinogen, converts to fibrin, hides bacteria from host
  • Protein A binds to Fc region of IgG, protects S. aureus from opsonization and phagocytosis
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8
Q

S. aureus exotoxin virulence factors (4 examples):

A

S. aureus exotoxin virulence factors:

  • Exfoliative toxins A and B: causes Staphylococcal Scalded Skin Syndrome (SSSS). Found in 5-10% of S. aureus strains
  • Enterotoxins: 8 distinct heat stable toxins that cause food poisoning with vomiting and diarrhea (rapid: 4 hours after ingestion)
  • Toxic Shock Syndrome toxin (TSST-1): heat and protease resistant toxin responsible for menstruation-associated toxic shock. Able to cross mucosal barriers.
  • Superantigens: binds to MHC II and T Cell Receptor –> Polyclonal T Cell activation –> Release of cytokines, leakage of endothelia
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9
Q

Where is S. aureus commonly found?

A

In the nose (30% of people are persistent carriers of S. aureus)

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10
Q

Staphylococcus aureus

​Diseases caused by exotoxin release (3 examples)

Diseases caused by direct organ invasion (8 examples/general idea)

A

Staphylococcus aureus

​Diseases caused by exotoxin release:

  • Gastroenteritis (food poisoning) caused by enterotoxins
  • Toxic Shock syndrome caused by TSST-1
  • Scalded skin syndrome caused by Exfoliative toxins A and B

Diseases caused by direct organ invasion:

  • Pneumonia
  • Meningitis
  • Osteomyelitis
  • Septic arthritis
  • Acute bacterial endocarditis
  • Skin infections
  • Bacteremia/sepsis
  • UTI
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11
Q
A
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12
Q

S. aureus food poisoning

Caused by ?

Symptoms ?

A

S. aureus food poisoning

Caused by S. aureus enterotoxins (heat stable, thus even if bacteria is killed by being cooked the toxin remains)

Symptoms: vomiting, diarrhea, and stomach cramping; no fever

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13
Q

S. aureus toxic shock syndrome

Caused by:

Symptoms:

Labs:

A

S. aureus toxic shock syndrome

Caused by:

  • Localized growth of S. aureus releases TSST-1 into the blood
  • Classic presentation: patients with superabsorbent tampons or nasal packing

Symptoms:

  • Macular erthematous rash - entire skin layer can desquamate
  • Vomiting
  • Hypotension
  • Fever

Labs:

  • Increased liver function tests (LFTs)
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14
Q

S. aureus Scalded Skin Syndrome

Also called ________ in newborns

Causes:

Symptoms:

A

S. aureus Scalded Skin Syndrome

Also called Ritter’s Disease in newborns

Causes:

  • S. aureus releases exfoliative toxins A and B

Symptoms:

  • Peri-oral erythema that expands to the entier body
  • Large bullea forms (no bacteria within bullae)

or

  • Bullous Impetigo: localized SSSS; fluid-filled blisters; S. aureus within blisters; erythema does not extend beyond blister

Note: A bulla is a fluid-filled sac or lesion that appears when fluid is trapped under a thin layer of your skin

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15
Q

Define the following:

Folliculitis:

Furuncles:

Carbuncles:

A

Define the following:

Folliculitis: infection around hair follicle; pus-filled lesions form around follicle. If occurs at base of eye it is called a stye

Furuncles: (aka boils); extension of folliculitis. Large, painful, underlying collection of necrotic tissue. Erythemitous, raised, swollen.

Carbuncles: Collection of furuncles; estend to deeper tissues; can lead to spread to other sites of body and bacteremia. Often include chills and fever which indicates systemic spread

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16
Q

Staph aureus is a common cause of bacteremia. Half of S. aureus bacteremia cases follow ________ or ________

A

Staph aureus is a common cause of bacteremia. Half of S. aureus bacteremia cases follow surgical procedures or prolonged catheter use

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17
Q

Staph aureus in blood can adhere to ____ tissues; can be sudden onset of high fever (103 to 105 F). High mortalitiy (50%). ____ destruction and embolisms to brain or lung can occur

A

Staph aureus in blood can adhere to heart tissues; can be sudden onset of high fever (103 to 105 F). High mortalitiy (50%). Valvular destruction and embolisms to brain or lung can occur

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18
Q

Endocarditis caused by Streptococcus viridans vs Staphylococcus aureus

A

Streptococcus viridans endocarditis often accumulates slowly overtime

Staphylococcus aureus endocarditis often has a rapid progression

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19
Q

Staphylococcus epidermidis

Tests:

Location in body:

Site of infection/symptoms:

A

Staphylococcus epidermidis

Tests:

  • Catalase (+)
  • Coagulase (-)
  • Novobiocin sensitive

Location in body:

  • Found on the skin; does not usually cause infection

Site of infection/symptoms:

  • Produces slime layer/biofilms (inhibits phagocytosis/increases Abx resistance) on foreign material, thus causes:
  • Endocarditis in artificial valves
  • Infection related to catheters, shunts, IVs, etc.
  • Artificial joint infections

Note: Since S. epidermidis is on the skin, it is a frequent contaminant in blood cultures

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20
Q

Staphylococcus saprophyticus

Tests:

Site of infection/symptoms:

A

Staphylococcus saprophyticus

Tests:

  • Catalase (+)
  • Coagulase (-)
  • Novobiocin resistant

Site of infection/symptoms:

  • ​UTI (2nd most common cause of UTI in young, sexually active women)
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21
Q

Staphylococcus aereus treatment

A

Staphylococcus aereus treatment

  • < 10% of Staph is sensitive to penicillin
  • MRSA (~60-70% of clinical isolates)
    • ​Vancomycin is 1st line of defence against MRSA
  • VRSA: Vancomycin resistance emerging
  • VISA: Vancomycin intermediate resistance SA (low level of resistance)
  • Community-acquired: more susceptible to sulfa sdrugs, tetracyclline, tigecycline
  • Hospital-acquired: requires linezolid, rifampin, clindamycin
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22
Q

What does a negative catalase test indicate?

A

That the bacteria is either Streptococci or Enterococci

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23
Q

What are the main catalase negative bacteria?

What kind of hemolytic activity do they have?

Study These Flashcards
A
  • Streptococcus pyogenes (GAS) - B hemolytic activity
  • Streptococcus agalactiae (GBS) - B hemolytic activity
  • Streptococcus pneumoniae - a hemolytic activity
  • Enterococcus faecalis - y hemolytic activity
  • Enterococcus faecium - y hemolytic activity
  • Viridans Streptococci - a hemolytic activity
24
Q

What are the 3 schemes used to classify Streptococci species?

Study These Flashcards
A
  • Lancefield antigen: C-polysaccharide; groups A through S
  • Hemolytic patterns: a, B, or y hemolysis
  • Biochemical properties

Side note:

  • B hemolytic streps are classified through Lancefield groupings
  • a and y hemolytic streps are classified by biochemical testing
25
What is the main example of Group A Strep (GAS)? What tests would confirm this bacteria?
* Streptococcus pyogenes * B-hymolytic and Bacitracin sensitive
26
What is the main example of Group B Strep (GBS)? What test would confirm this bacteria?
* Streptococcus agalactiae * B-hemolytic
27
What are the main Group D bacteria?
* Enterococcus (technically not a Streptococcus but its own Genus) * S. bovis (non-Enterococcal Group D Strep)
28
**S. pneumoniae** Does it have the Lancefield antigen? \_\_-hemolytic
**S. pneumoniae** No Lancefield antigen a-hemolytic
29
**Streptococcus viridans** Does it have lancefield antigens? What is the most important species?
**Streptococcus viridans** Yes it has variuos lancefield antigens The most important species is Streptococcus mutans (dental caries) Note: Streptococcus viridans is a diverse group of many species
30
**S. pyogenes (GAS) _cloaking_ virulence factors**
**S. pyogenes (GAS) virulence factors** **Cloaking Devices**: * **M-Proteins** and M-like proteins: * Antiphagocytic factor * 2 types: **Class I** and **Class II**; only **Class I** is associated with **rheumatic fever** * **Hyaluronic acid capsue (present in some)** * **​Interferes with phagocytosis** * Non-immunogenic (looks like host connective tissue) * Associated with invasive infections
31
How does S. pyogenes M protein lead to the development of rheumatic fever?
Antibodies against M protein cross react with heart cells
32
**S. pyogenes (GAS) _cell destruction_ virulence factors**
**S. pyogenes (GAS) _cell destruction_ virulence factors** * **Hemolysins**: Makes pores in host membranes - Cell destruction * **Streptolysin S**: Major factor leading to B-hemolysis on blood agar * **Streptolysin O**: * Oxygen-sensitive hyemolysin, doesn't contribute to B-hemolysis on blood agar plates grown aerobically * Immunogenic - can be used to diagnose rheumatic fever and glomerulonephritis (**anti-streptolysin O antibody test = ASO test = indicates Strep pyogenes infection**)
33
**S. pyogenes (GAS) _toxic_ virulence factors**
**S. pyogenes (GAS) _toxic_ virulence factors** * **Pyrogenic exotoxins:** * **​Phage-encoded superantigens** * **Cross-link MHC II to TCR** * Induce T-cell activation and massive cytokine production * Results in non-productive and non-specific immune response
34
List of diseases that S. pyogenes (GAS) can cause
* Pharyngitis "strep throat" * Scarlet fever * Acute Rheumatic Fever/Rheumatic Fever * Acute Glomerulonephritis * Non-Suppurative Sequelae * Skin infections including: * Impetigo * Erysipelas * Cellulitis * Necrotizing fasciitis "flesh-eating disease" (often with STSS)
35
**Pharyngitis "strep throat" caused by S. pyogenes (GAS)** ## Footnote **Symptoms**:
**Pharyngitis "strep throat" caused by S. pyogenes (GAS)** **Symptoms**: * Fever \> 102, chills, headache * Painful to swallow Notes: * Common in 5-15 year-olds (but possible in alll ages) * Highest incidence in winter and spring * Self-limiting, but treatment advisable to avoid sequelae
36
**Scarlet Fever caused by S. pyogenes (GAS)** ## Footnote **Symptoms:**​
**Scarlet Fever caused by S. pyogenes (GAS)** **Symptoms:**​ * Diffuse erythematous rash * Begins on chest and spreads to extremities * Caused by S. pyogene superantigen exotoxins * Strawberry tongue Note: Scarlet fever may accompany pharyngitis "strep throat"
37
How to differentiate skin infections caused by Staphylococcus aureus vs a strep species
If purulent/pus filled skin infection = likely Staphylococcus aureus If skin infection with no pus = likely a strep bacteria
38
**Skin infections caused by S. pyogenes (GAS)** **Empetigo (aka Pyoderma) and Erysipelas** **Description and Symptoms**
**Skin infections caused by S. pyogenes (GAS)** * **Impetigo (aka Pyoderma)** * **​**Superficial infection, common in children, common in warm/humid summer months * **Erysipelas** * Infection of the dermis; _sharply demarcated edge_ * Localized pain, erythema, fever, and chills * Leukocytosis * Most common in young and elderly
39
**Skin infections caused by S. pyogenes (GAS)** **Cellulitis** **Description/Signs:**
**Skin infections caused by S. pyogenes (GAS)** **Cellulitis** **Description/Signs:** Deeper dermal infection. _Not_ sharply demarcated. Invasion mediated (not toxin mediated)
40
**Skin infections caused by S. pyogenes (GAS)** **Necrotizing Fasciitis**
* Necrosis of connective tissue, fat tissue, and lymphatics * Preceded by cellulitis, bullae, and gangrene * Extremely painful with rapid progression along fascial plane * Typically requires debridement * Often accompanied by Streptococcal Toxic Shock Syndrome (STSS) * Due to pyrogenic superantigen exotoxins
41
Non-Supportive Sequelae caused by GAS
Autoimmune reactions post-GAS infection (immunologic)
42
**Acute Rheumatic Fever/Rehumatic Fevere caused by GAS**
* **Antibodies raised against M-protein and other bacterial antigens cross-react with heart tissues and muscle/valves** * **Follows pharyngeal "strep throat" infections only** * Immune reaction to joints, CNS, and skin also possible
43
**Acute Glomerulonephritis (AGN) caused by GAS**
* Follows pharyngeal and skin infections * Antibody-antigen complexes deposit on glomerular basement membrane - leads to complement fixation and inflammation (Type III Hypersensitivity)
44
GAS treatment and prevention
* _Highly susceptible to **Penicillin G**_ * Mixed infections with S. aureus should include vancomycin * Increasing frequency of tetracycline and macrolide resistance * Aminoglycosides - high level of resistance observed * Adequate treatment of Streptococcal pharyngitis within 10 days of onset will prevent rheumatic fever * Serious soft tissue infections require drainage and debridement * Patients with history of rheumatic fver may required long term antibiotic prophylaxis
45
S. pyogenes (GAS) tests
* Catalase (-) * B-Hemolysis * Bacitracin sensitive
46
**S. agalactiae = Group B Strep (GBS)** ## Footnote **Tests:** **Properties:**
**Tests:** * **Catalase (-)** * **B-Hemolytic** * **Bacitracin Resistant** * **Lancefield B antigen** * **Produces CAMP factor** (not to be confused with cyclic AMP), which is a diffusible extracellular hemolytic heat-stable protein that is synergistic with beta-lysin produced by Staph aureus resulting in enhanced lysin of RBCs/enlarges zone of hemolysis formed by S. aureus **Properties**: * Gram-positive cocci in chains * Polysaccharide capsule (important for virulence)
47
Streptococcus agalactiae (GBS) is the largest caused of neonatal \_\_\_\_, \_\_\_\_, and \_\_\_\_ GBS colonizes the ________ and \_\_\_\_\_\_\_\_. Likelihood of infant colonization increase when mother is colonized with large numbers of organisms. Risks include premature delivery, prolonged membrane rupture, intrapartum fever, and post-partum disease
Streptococcus agalactiae (GBS) is the largest caused of neonatal _meningitis_, _sepsis_, and _pneumonia_ GBS colonizes the _lower GI tract_ and _genitourinary tract_. Likelihood of infant colonization increase when mother is colonized with large numbers of organisms. Risks include premature delivery, prolonged membrane rupture, intrapartum fever, and post-partum disease
48
**Streptococcus agalactiae (GBS) Disease** ## Footnote **Early onset neonatal disease:** **Late onset disease:** **Infections in men/non-pregnant women:**
**Streptococcus agalactiae (GBS) Disease** **Early onset neonatal disease:** * Acquired in utero or at birth and develops during 1st week * Bacteremia, meningitis, pneumonia * Neonates present with non-specific signs such as fever, vomiting, poor eating, and irritability **Late onset disease:** * Acquired from exogenous source * Develops between 1 week and 3 months of age * Bacteremia with meningitis **Infections in men/non-pregnant women:** * Generally older or immunocompromised * Bacteremia, pneumonia, bone/joint infections, skin/soft tissue Note: Neurologic complications are common
49
**Streptococcus agalactiae (GBS)** ## Footnote **Diagnosis:** **Treatment:**
**Streptococcus agalactiae (GBS)** **Diagnosis:** * Primarily done by culture * Catalase (-), B-heomolysis, Bacitracin resistant **Treatment:** * Organisms are sensitive to penicillin; howver, start with borad spectrum antibiotics until GBS is confirmed * Women testing positive during pregnancy (tested 35-37 weeks) should be given IV Abxs during labor (at least 4 hours prior)
50
**Streptococcus pneumoniae (aka Pneumococcus)** ## Footnote **Tests:** **Location:** **Properties:** **Diseases:**
**Streptococcus pneumoniae (aka Pneumococcus)** **Tests:** * Catalase (-) * a-hemolytic * Optochin sensitive **Location:** * Upper respiratory tract **Properties:** * Virulence factor: _Capsule_ * Arranged in pairs or short chains **Diseases:** * _Most common cause of bacterial meningitis in adults/children_ * _Pneumonia_ * _Bacteremia_ * _Otisis media_ (middle ear infections in young children)
51
**Streptococcus pneumoniae diseases (4 main examples)**
* **Pneumonia**: develops as bacteria multiply in alveolar spaces. * Patients with splenic dysfunction = high mortality * **Otisis media**: middle ear infections in young children * **Meningitis**: in young children and adults * **Bacteremia** * Endocarditis can also occur
52
**Viridans Streptococci** ## Footnote **Tests:** **Location:** **Diseases:**
**Viridans Streptococci** **Tests:** * Catalase (-) * a-hemolytic * Optochin resistant **Location:** * _Oral cavity_, also GI/GU tract **Diseases:** * S. mutans and S. mitis cause _dental caries_ * Dental manipulations can send bacteria into the blood where they can target the heart/valves. Repeated builup of these bacteria can lead to _Subacute Endocarditis_
53
**Enterococcus** ## Footnote **Tests:** **Common examples:** **Location:** **Virulence:**
**Enterococcus** **Tests:** * Catalase (-) * y-hemolysis * Grows in bile * Growth in 6.5% NaaCl and (+) PYR status **Common examples:** * E. faecium * E. faecalis **Location:** * Normal flora of intestinal tract (large and small intestine) **Virulence:** * Forms biofilms on tissues * Antibiotic resistances
54
What patients are most at risk of developing Enterococcus infections?
Patients hospitalized for prolonged periods and treated with broad spectrum antibiotics, particularly cephalosporins
55
Enterococcus common infections/diseases
* UTIs * Wound infections * Endocarditis * Bacteremia and sepsis following IV catheters
56
**Streptococcus bovis (Group D Streptococcus)** ## Footnote **Tests:** **Location:** **Diseases:**
**Streptococcus bovis (Group D Streptococcus)** **Tests:** * Catalase (-) * y-hemolysis * Grows in bile * Does _not_ grow in 6.5% NaCl and has (-) PYR status **Location:** * Colonizes gut **Diseases:** * Bacteremia and sub-acute endocarditis in colon cancer patients
57
What antibiotic is Enterococcus resistant to?
Vancomycin Enterococcus has also transmitted this resistance to Staphylococcus aureus

Block 2 - Week 2 (2 decks)

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