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Foundations of Disease > Exam 1: Gram-Positive Cocci > Flashcards

Exam 1: Gram-Positive Cocci Flashcards

1
Q

Pyogenic Cocci

A

Pus producing organisms:

  • Gram ⊕
    • Staphylocci
    • Streptococci
  • Gram ⊖
    • Neisseria spp
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2
Q

Pyogenic pathogens cause ___ through ___.

A

acute suppurative infections

neutrophil mobilization

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3
Q

Staphylococcus

Overview

A
  • Pyogenic bacteria
  • Survive for a long time on dry inanimate objects
  • Common source of hospital acquired infections
  • Associated diseases includes:
    • Abscess
    • Food poisoning
    • Osteomyelitis
    • Endocarditis
    • Toxin related diseases
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4
Q

Staphylococcus

Characteristics

A
  • Large gram ⊕ cocci
  • Usually grouped in irregular “grape-like” clusters
  • Divides in 3 planes
  • Facultative anaerobes
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5
Q

The most pathogenic species of Staphylococcus genus is…

A

Staph. aureus

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6
Q

Staph. aureus is part of the normal flora of the…

A

skin, nasal pharynx, urethra, and eye

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7
Q

S. aureus is resistant to __ and can therefore be acquired from ___.

A

drying

fomites

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8
Q

S. aureus colonizes ~ 20% of healthy individuals in the…

A

nasal nares

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9
Q

Type of disease caused by S. aureus depends on…

A
  • Location in the body
  • Environment within the host
  • Virulence factors expressed by that particular strain
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10
Q

S. aureus

Surface Components

A
  1. Capsule
  2. Protein A
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11
Q

S. aureus

Capsule

A

Found in some strains:

  • Prevents phagocytosis
  • Promotes adherence to cells and prosthetic devices
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12
Q

S. aureus

Protein A

A
  • Binds Fc terminus of IgG
  • Prevents opsonization and Fc mediated phagocytosis
  • Prevents IgG complement activation
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13
Q

S. aureus

Enzymes

A
  1. Catalase
  2. Coagulase
  3. Hyaluronidase
  4. Lipases, Proteases, DNAases
  5. Beta lactamase
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14
Q

S. aureus

Catalase

A

Converts H2O2 ⇒ H2O + O2

Limits respiratory burst of phagocytes

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15
Q

S. aureus

Coagulase

A

Converts fibrinogen ⇒ fibrin

Causes clotting & promotes abscess formation

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16
Q

S. aureus

Hyaluronidase

A

Hydrolyzes CT matrix

Enhances bacterial spread

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17
Q

S. aureus

Lipases, Proteases, DNAses

A

Allows tissue and cell digestion

Facilitates substrate use & enhances virulence

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18
Q

S. aureus

Beta Lactamase

A

Inactivates pencillin and ampicillin

Plasmid mediated

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19
Q

S. aureus

Toxins

A

A single isolate can produce several exotoxins:

  1. Enterotoxins
  2. Exfoliatin
  3. Toxic Shock Syndrome Toxin (TSST-1)
  4. Leukocidins
  5. Hemolysins
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20
Q

S. aureus

Enterotoxins

A

7 serotypes (A-G) produced by 50% of S. aureus strains

Responsible for Staph. food poisoning

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21
Q

S. aureus

Exfoliatin

A

Causes skin sloughing in scaled skin syndrome

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22
Q

S. aureus

Toxic Shock Syndrome Toxin

(TSST-1)

A

Superantigen

Induces excessive cytokine release from T-cells

Results in fever, shock, and multi-organ failure

23
Q

S. aureus

Leukocidins

A

Pore forming proteins that lyse WBCs

24
Q

S. aureus

Hemolysins

A

Pore forming proteins that lyse RBCs

25
Q

S. aureus

Disease Causing Mechanism

A
  • Most commonly causes disease by inciting an acute inflammatory reaction
    • Many neutrophils mobilized to site
    • Bacterial and host derived chemotactic factors
  • Abscess formation common
    • Walled off structure makes it harder for immune components and abx to penetrate
  • May remain localized within abscess or disseminate to other sites
26
Q

S. aureus

Lab Characteristics

A
  • Catalase ⊕
    • Differentiates all Staph (⊕) from Strep (⊖)
  • Coagulase ⊕
  • Beta-hemolytic on blood agar
    • Golden colonies
  • Grow on 7.5% NaCl Mannitol
    • All Staph. species grow under high salt conditions
    • Only S. aureus ferments mannitol
  • Nucleic acid tests
    • Used to ID S. aureus from clincal specimens
27
Q

S. aureus

Treatment

A
  • All Staph resistant to penicillin
    • Due to Beta Lactamase
      • Hydrolyzes beta lamtam ring of penicillin
    • Transmitted by plasmid
  • Semi-synthetic penicillins are effective
    • Nafcillin
    • Methicillin
  • Cephalosporin agents effective
  • Strains that are methicillin resistent are resistant to all beta lactam abx
    • Encoded by a penicillin binding protein (PBP2’)
  • Vancomycin may be used to treat MRSA
    • Resistance also starting to develop against this drug
28
Q

S. aureus

Immunity & Prevention

A
  • Immunity
    • Clearance mediated by opsonizing IgG
    • Incomplete and short-lived
      • Repeated infections possible
  • Best prevention
    • Good handwashing
    • Good disinfectant practices
29
Q

Staph. epidermidis is normal flora of the…

A

skin, nose, and throat

30
Q

Staph. epidermidis causes infections of…

A

prosthetic devices, shunts, grafts, and catheters

31
Q

Staph. epidermidis is the most common cause of…

A

prosthetic valve endocarditis

32
Q

Staph. epidermidis major virulence factor is…

A

high molecular weight polysaccharide slime

Enchances adherence.

33
Q

Staph. epidermidis

Lab Characteristics

A
  • Gram ⊕ cocci
  • Catalase ⊕
  • Coagulase ⊖
  • Non-hemolytic ⇒ gamma-hemolytic
    • White colonies on blood agar
34
Q

Staph. saprophyticus is a common cause of…

A

UTI in young healthy women

35
Q

Staph. saprophyticus

Lab Characteristics

A
  • Gram ⊕ cocci
  • Catalase ⊕
  • Coagulase ⊖
  • Non-hemolytic ⇒ gamma-hemolytic
  • White colonies on blood agar
36
Q

Streptococcus

Diseases

A

Includes:

  • Pharyngitis
  • Otitis media
  • Meningitis
  • Pneumonia
  • Sepsis
37
Q

Streptococcus

Classification

A

Classified in three ways:

  1. Serologically
    • Lancefield grouping
  2. Patterns of hemolysis
  3. Species
38
Q

Streptococcus

Characteristics

A
  • Gram ⊕ cocci arranged in chains
  • Catalase ⊖
  • Facultative anaerobe
    • Metabolism is fermentative
    • Tolerates and can grow in oxygen
    • Growth enhanced by 5-10% CO2
  • Small translucent colonies
39
Q

Lancefield’s Groupings

A

Serological grouping of Strep based on major cell wall carbohydrate Ag.

A⇒U

Some species cannot be assigned to any of these groups.

40
Q

Group A Strep includes ___ which causes ___.

A

Strep. pyogenes

Pharyngitis & Scarlet fever

41
Q

Group B strep includes ___ which causes ___.

A

Strep. agalactiae

Neonatal sepsis & Meningitis

42
Q

Group D strep includes ___ which causes ___.

A

Strep. bovis

Endocarditis & Bacteremia

43
Q

Non-Typable Strep

A

Some species cannot be grouped according to Lancefield system.

Some important pathogens include:

  • Viridans group ⇒ endocarditis
    • S. mutans
    • S. sanguis
    • S. salivarius
  • S. pneumonia
    • Pneumonia, meningitis, otitis media
  • Peptostreptococcus
    • Strict anerobes
44
Q

Enterococcus

Characteristics

A
  • Gram ⊕ cocci
    • Formerly part of Group D Strep
    • Now seperate genera
  • Opportunistic pathogens
45
Q

Enterococcus are normal flora of…

A

skin, URT, GI and urogenital tract

46
Q

Enterococcus that causes infective endocarditis, UTI, bacteremia/septicemia, and meningitis are…

A

Enterococcus faecalis

&

Enterococcus faecium

47
Q

Strepococci are commonly classified based on type of ___ when grown on blood agar plates.

A

hemolysis

48
Q

Alpha (α) Hemolysis

A

Partial hemolysis of RBCs

Colony surrounded by green halo

Includes Strep. viridans & Strep. pneumonia

49
Q

Beta (β) Hemolysis

A

Complete hemolysis of RBCs

Colonies surrounded by a clear zone

Includes S. pyogenes and S. agalactiae

50
Q

Gamma (γ) Hemolysis

A

Non-hemolytic

No change in blood agar

Includes Group D Strep and Enterococci

51
Q

Bacitracin Sensitivity

A

Used to distinguish between two β-hemolytic Streps:

Group A ⇒ bacitracin sensitive ⇒ S. pyogenes

Group B ⇒ bacitracin resistant ⇒ S. agalactiae

52
Q

Optochin Sensitivity

A

Used to distinguish between α-hemolytic Strep:

  • S. pneumoniae* ⇒ sensitive
  • Viridans group* ⇒ resistant
53
Q

Gram Positive Chart

A

Foundations of Disease (46 decks)

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