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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
S. aureus Disease Causing Mechanism
* 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
S. aureus Lab Characteristics
* **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
S. aureus Treatment
* **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
S. aureus Immunity & Prevention
* **Immunity** * Clearance mediated by **opsonizing IgG** * **Incomplete and short-lived** * Repeated infections possible * **Best prevention** * Good handwashing * Good disinfectant practices
29
Staph. epidermidis is normal flora of the...
skin, nose, and throat
30
Staph. epidermidis causes infections of...
prosthetic devices, shunts, grafts, and catheters
31
Staph. epidermidis is the most common cause of...
prosthetic valve endocarditis
32
Staph. epidermidis major virulence factor is...
high molecular weight **polysaccharide slime** Enchances adherence.
33
Staph. epidermidis Lab Characteristics
* **Gram ⊕ cocci** * **Catalase ⊕** * **Coagulase ⊖** * **Non-hemolytic** ⇒ gamma-hemolytic * White colonies on blood agar
34
**Staph. saprophyticus** is a common cause of...
UTI in young healthy women
35
Staph. saprophyticus Lab Characteristics
* Gram ⊕ cocci * Catalase ⊕ * Coagulase ⊖ * Non-hemolytic ⇒ gamma-hemolytic * White colonies on blood agar
36
Streptococcus Diseases
Includes: * Pharyngitis * Otitis media * Meningitis * Pneumonia * Sepsis
37
Streptococcus Classification
_Classified in three ways:_ 1. **Serologically** * Lancefield grouping 2. **Patterns of hemolysis** 3. **Species**
38
Streptococcus Characteristics
* **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
Lancefield's Groupings
**Serological grouping of Strep based on major cell wall carbohydrate Ag.** A⇒U Some species cannot be assigned to any of these groups.
40
**Group A** Strep includes ___ which causes \_\_\_.
Strep. pyogenes Pharyngitis & Scarlet fever
41
**Group B** strep includes ___ which causes \_\_\_.
Strep. agalactiae Neonatal sepsis & Meningitis
42
**Group D** strep includes ___ which causes \_\_\_.
Strep. bovis Endocarditis & Bacteremia
43
Non-Typable Strep
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
Enterococcus Characteristics
* **Gram ⊕ cocci** * Formerly part of Group D Strep * Now seperate genera * Opportunistic pathogens
45
**Enterococcus** are normal flora of...
skin, URT, GI and urogenital tract
46
**Enterococcus** that causes _infective endocarditis, UTI, bacteremia/septicemia, and meningitis_ are...
*Enterococcus faecalis* & *Enterococcus faecium*
47
Strepococci are commonly classified based on type of ___ when grown on blood agar plates.
hemolysis
48
Alpha (α) Hemolysis
**Partial hemolysis of RBCs** Colony surrounded by _green halo_ Includes ***Strep. viridans*** & ***Strep. pneumonia***
49
Beta (β) Hemolysis
**Complete hemolysis of RBCs** Colonies surrounded by a _clear zone_ Includes ***S. pyogenes*** and ***S. agalactiae***
50
Gamma (γ) Hemolysis
**Non-hemolytic** _No change in blood agar_ Includes ***Group D Strep*** and ***Enterococci***
51
Bacitracin Sensitivity
Used to distinguish between _two β-hemolytic Streps_: **Group A** ⇒ bacitracin **sensitive** ⇒ *S. pyogenes* **Group B** ⇒ bacitracin **resistant** ⇒ *S. agalactiae*
52
Optochin Sensitivity
Used to distinguish between _α-hemolytic Strep_: * S. pneumoniae* ⇒ **sensitive** * Viridans group* ⇒ **resistant**
53
Gram Positive Chart

Foundations of Disease (46 decks)

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