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

Gram-positive cocci Flashcards

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?

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?

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
Q

What is the main example of Group A Strep (GAS)?

What tests would confirm this bacteria?

A
  • Streptococcus pyogenes
  • B-hymolytic and Bacitracin sensitive
26
Q

What is the main example of Group B Strep (GBS)?

What test would confirm this bacteria?

A
  • Streptococcus agalactiae
  • B-hemolytic
27
Q

What are the main Group D bacteria?

A
  • Enterococcus (technically not a Streptococcus but its own Genus)
  • S. bovis (non-Enterococcal Group D Strep)
28
Q

S. pneumoniae

Does it have the Lancefield antigen?

__-hemolytic

A

S. pneumoniae

No Lancefield antigen

a-hemolytic

29
Q

Streptococcus viridans

Does it have lancefield antigens?

What is the most important species?

A

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
Q

S. pyogenes (GAS) cloaking virulence factors

A

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
Q

How does S. pyogenes M protein lead to the development of rheumatic fever?

A

Antibodies against M protein cross react with heart cells

32
Q

S. pyogenes (GAS) cell destruction virulence factors

A

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
Q

S. pyogenes (GAS) toxic virulence factors

A

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
Q

List of diseases that S. pyogenes (GAS) can cause

A
  • 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
Q

Pharyngitis “strep throat” caused by S. pyogenes (GAS)

Symptoms:

A

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
Q

Scarlet Fever caused by S. pyogenes (GAS)

Symptoms:​

A

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
Q

How to differentiate skin infections caused by Staphylococcus aureus vs a strep species

A

If purulent/pus filled skin infection = likely Staphylococcus aureus

If skin infection with no pus = likely a strep bacteria

38
Q

Skin infections caused by S. pyogenes (GAS)

Empetigo (aka Pyoderma) and Erysipelas

Description and Symptoms

A

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
Q

Skin infections caused by S. pyogenes (GAS)

Cellulitis

Description/Signs:

A

Skin infections caused by S. pyogenes (GAS)

Cellulitis

Description/Signs: Deeper dermal infection. Not sharply demarcated. Invasion mediated (not toxin mediated)

40
Q

Skin infections caused by S. pyogenes (GAS)

Necrotizing Fasciitis

A
  • 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
Q

Non-Supportive Sequelae caused by GAS

A

Autoimmune reactions post-GAS infection (immunologic)

42
Q

Acute Rheumatic Fever/Rehumatic Fevere caused by GAS

A
  • 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
Q

Acute Glomerulonephritis (AGN) caused by GAS

A
  • Follows pharyngeal and skin infections
  • Antibody-antigen complexes deposit on glomerular basement membrane - leads to complement fixation and inflammation (Type III Hypersensitivity)
44
Q

GAS treatment and prevention

A
  • 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
Q

S. pyogenes (GAS) tests

A
  • Catalase (-)
  • B-Hemolysis
  • Bacitracin sensitive
46
Q

S. agalactiae = Group B Strep (GBS)

Tests:

Properties:

A

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
Q

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

A

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
Q

Streptococcus agalactiae (GBS) Disease

Early onset neonatal disease:

Late onset disease:

Infections in men/non-pregnant women:

A

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
Q

Streptococcus agalactiae (GBS)

Diagnosis:

Treatment:

A

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
Q

Streptococcus pneumoniae (aka Pneumococcus)

Tests:

Location:

Properties:

Diseases:

A

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
Q

Streptococcus pneumoniae diseases (4 main examples)

A
  • 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
Q

Viridans Streptococci

Tests:

Location:

Diseases:

A

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
Q

Enterococcus

Tests:

Common examples:

Location:

Virulence:

A

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
Q

What patients are most at risk of developing Enterococcus infections?

A

Patients hospitalized for prolonged periods and treated with broad spectrum antibiotics, particularly cephalosporins

55
Q

Enterococcus common infections/diseases

A
  • UTIs
  • Wound infections
  • Endocarditis
  • Bacteremia and sepsis following IV catheters
56
Q

Streptococcus bovis (Group D Streptococcus)

Tests:

Location:

Diseases:

A

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
Q

What antibiotic is Enterococcus resistant to?

A

Vancomycin

Enterococcus has also transmitted this resistance to Staphylococcus aureus

Block 2 - Week 2 (2 decks)

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