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D1 Microbiology > Written Exam 3 Slides groups 4 - 7 > Flashcards

Written Exam 3 Slides groups 4 - 7 Flashcards

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1
Q

What do staphylococcus look like on a slide?

A

Staphyl = clusters

Cocci = spheres

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2
Q

Is staphylococcus gram + or gram -

A

Gram +

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3
Q

What is one of the key tests for determining if an unknown is staphylococci vs. streptococci?

A
  • If positive for staphylococci = produces BUBBLES
  • Catalase breaks down H2O2 produced during oxidation metabolism
  • Streptococci don’t produce catalase
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4
Q

What are the clinically important species of staphylococcus

A
  • Staphylococcus aureus
    • Most virulent staphylococcal species
    • Produces a variety of diseases
  • Staphylococcus epidermidis
    • Low virulence
    • Normal microbiota of the skin
    • Causes opportunistic infections
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5
Q

Explain how the Coagulases production test is used to determine the type of bacterium

A
  • Coagulases production
    • Coagulase + serum factor (fibrinogen in serum) -> fibrin (clot)
      • Liquid in tube then produces a solid (clot)
    • Distinguishes S. aureus from other staphylococci (ie. S. epidermidis)
      • S. aureus = coag (+)
      • S. epidermidis = coag (–)
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6
Q

Describe the Blood agar = used for pigment production test and the results

A
  • Gold colonies = S. aureus (gold = Au)
  • White colonies = S. epidermidis (white skin)
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7
Q

Explain Hemolysis on Blood Agar

A
  • Beta-hemolysis = complete hemolysis
    • S. aureus
  • Alpha-hemolysis = incomplete hemolysis -> green pigment (breaking down RBC, not completely)
  • Gamma-hemolysis = no hemolysis
    • S. epidermidis
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8
Q

Explain how mannitol and halotolerance is used to determine the microorganism

A

Fermentation of Mannitol and Halotolerance (both grown on agar, only S. aureus ferments mannitol = yellow) = selective and differential media!!!

  • Mannitol salt agar contains 7.5% NaCl, which inhibits the growth of many organisms except staphylococci which are halotolerant (facultative halophile) ie. On skin
    • Mannitol salt agar contains mannitol = organisms that ferment mannitol -> detected by a change in the pH indicator from red to yellow
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9
Q

Describe staphylococcus epidermidis disease overview

A
  • Informal name = “staph epi”
  • Frequent contaminant in clinical samples
  • Relatively avirulent although production of a slime layer helps it adhere to devices forming biofilms (catheters, shunts, prosthetic joints, etc.)
  • When introduced into deeper tissues or a normally sterile site, it causes opportunistic infections (ie. In blood)
  • Opportunistic infections usually acquired during a hospital stay
  • Infections include subacute endocarditis, infections of foreign bodies (ie. Catheters, shunts, prosthetic joints, etc) and urinary tract infections
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10
Q

Describe the Epidemiology of S. aureus

A
  • Humans are the main reservoir (hands and nose)
    • About 30% of healthy adults are nasal carriers (most healthcare workers)
    • May also colonize skin and mucous membranes
    • Server as a source of infection to themselves and others
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11
Q

Explain the Transmission of S. aureus

A

Transmission of S. aureus [high tolerance to salt and desiccation (drying conditions)]

  • Direct skin to skin contact
  • Indirect contact via fomites (inanimate objects: towel, door, etc)
  • Ingestion of contaminated food
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12
Q

Staphylococcus aureus Diseases:

A
  • Causes more frequent and varied types of disease than any other human pathogen
  • Abscesses (pool of puss surrounded by fibrin)
  • Toxin-mediated:
    • Staphylococcal food poisoning
    • Scalded skin syndrome
    • Toxic shock syndrome
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13
Q

What is an abscess?

A
  • Collection of pus surrounded by fibrin
    • Pus contains debris consisting of dead PMNs and epithelial cells, dead and live bacteria and edema fluid
    • Pyogenic = pus producing
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14
Q

What is pyogenic

A

pus producing abscess

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15
Q

Explain abscesses by S. aureus

A
  • Acute inflammation leads to recruitment of PMNs and some staphylococci are capable of not only surviving but also killing and lysing many of the PMNs
  • Patients with chronic granulomatous disease are highly susceptible to developing frequent and serious S. aureus infections
    • PMNs in these patients are unable to make sufficient hydrogen peroxide to set off the oxidative killing pathway
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16
Q

What disease is patients increase their suseptibility to developing frequent and serious S. aureus infections, and why?

A
  • Patients with chronic granulomatous disease are highly susceptible to developing frequent and serious S. aureus infections
    • PMNs in these patients are unable to make sufficient hydrogen peroxide to set off the oxidative killing pathway
17
Q

What are virulence factors

A
  • The genetic, biochemical or structural features that enable an organism to produce disease
  • Pathogenesis may depend on a single or multiple virulence factors.
    • For most disease caused by S. aureus, pathogenesis depends on the combined actions of several virulence factors
18
Q

What are the major virulence factors of S. aureus?

A
  • Catalase: counteracts phagocytes’ ability to kill bacteria by production of reactive oxygen species
  • Protein A: a surface protein that binds to the Fc region of IgG antibodies
  • Coagulase: forms fibrin clot and forms camouflage around bacteria (produce toxin to break up the clot)
  • Leukocidin: an exotoxin that lyses white blood cells by forming pores in their membranes
  • Fibronectin-binding proteins:
    • Expressed on surface of S. aureus
    • Allow bacteria to invade epithelial and endothelial cells and to attach to exposed fibronectin in wounds
  • Exotoxins (different types to be discussed later)
  • Pennicinilase
19
Q
A

C. prevent phagocytosis

  • Coagulase = surrounds w/host protins in fiber coat
  • Protein A = binds to Fc region on IgG and can no longer function as opsinin
20
Q

What are the localized cutaneous infections caused by S. aureus? name and describe

A
  • S. aureus is the most common cause of pyogenic skin infections
  • Pyogenic infections are characterized by the formation of an abscess
  • Diseases:
    • Folliculitis = infection of hair follicle
      • superficial abscess
      • Usually mild, resolves or progresses to furuncle
    • Furuncle = aka boil; large painful lesion extends from hair follicle to surrounding tissues
      • Abscesses in the skin involving subcutaneous tissue
      • Resolves or progresses to carbuncle
    • Carbuncle = multiple interconnected abscesses forming form the aggregation of furuncles
      • Extends deeper into the tissue
      • Requires debridement (removal of dead tissue) and antibiotics
    • Impetigo = Most common type of pyoderma, skin infection characterized by pus production
      • Abraded skin(diapers)/insect bite/burn gets infected
      • Small flattened red patches->pus filled vesicles->rupture and crust over
      • Common among infants and young children
      • Itchy, highly contagious
      • Also caused by streptococcus pyogenes
21
Q

Cellulitis is what?

A
  • Alternatively, staphylococci can spread in the subcutaneous or submucosal tissue
  • Diffuse inflammation (appears as an inflammation and NOT concentrated)
22
Q

What are the Causes of S. aureus disease

A
  • Infection (colonization) CAUSES DISEASE
  • Intoxication (toxin production to exotoxin) NO INFECTION INVOLVED
  • Infection and intoxication (colonization then exotoxin)
23
Q

What is food poisioning?

A
  • In general, gastroenteritis is commonly caused by bacteria, viruses or toxins
    • When it is caused by a toxin and not an infection = food poisoning
24
Q

What are Toxin Mediated Diseases (name)

A
  • Staphylococcal food poisoning
  • Staphylococcal scalded skin syndrome (SSSS)
  • Toxic Shock Syndrome
25
Q

Staphylococcal food poisoning

A

Staphylococcal food poisoning **Not an established infection**

  • Intoxication not an infection
    • Rapid onset usually within 4 hours
    • Rapid recovery usually within 24 hours
  • Symptoms: nausea and vomiting
    • No fever
26
Q

Staphylococcal enterotoxin

A
  • Staphylococcal enterotoxin is a type of exotoxin
    • Heat stable @ 100 deg C for 30 min
    • Foods most commonly contaminated: ham, potato salad with mayonnaise left unrefrigerated
27
Q

Toxic Shock Syndrome

A
  • Localized infection, systemic intoxication
  • Caused by Toxic Shock Syndrome Toxin 1 (TSST-1)
    • An exotoxin that induces fever, vomiting, rash and shock
    • Acts as a potential superantigen
    • TSST-1 causes 75% of all cases (TSS can also be caused by Streptococci) – like impetigo
28
Q

Superantigens

A
  • Bacterial or viral virulence factors that nonspecifically activate many T cells resulting in excessively pro-inflammatory cytokine production
  • Causes symptoms of high fever, malaise, nausea, vomiting, diarrhea, hypotension that sometimes leads to fatal shock
29
Q

Toxic Shock Syndrome

A
  • Symptoms: abrupt onset of high fever, red sunburn-like rash, desquamation, hypotension, multisystem organ failure
  • Classically it affected menstruating women using high absorbance tampons but can also occur in men and children with wound infections
30
Q

Staphylococcal Scalded Skin Syndrome (SSSS)

A
  • Localized infection, systemic intoxication
  • Caused by exfoliative toxin
    • An exotoxin that causes desquamation of the skin
    • Also acts as superantigen, albeit weaker than TSST-1
  • Symptoms: erythema followed by desquamation
  • No scarring (usually not painful)
  • Typically affects neonates and infants
  • Potential complication: a secondary infection of denuded (compromised stripped skin) area
31
Q

Management of staphylococcal infection

A
  • Control/prevention of nosocomial infections
    • Careful hand hygiene
    • Adequate antisepsis and disinfection (living tissue chemical methods)
    • Isolation of patients with open skin wounds
    • Boils, carbuncles may require minor surgery to drain puss and remove dead tissue
    • Antibiotic treatment often follows debridement
    • Staphylococci produce penicillinase (beta lactamase breaks penicillin ring and cannot treat with penicillin)
32
Q

Explain Methicillin resistant S. aureus (MRSA) and Vancomycin resistant S. aureus (VRSA)

A

Methicillin resistant S. aureus (MRSA)

  • Produce penicillin binding protein PBP-2a
    • Codes for a new peptidoglycan transpeptidase with a low affinity for all currently available beta lactam antibiotic (for cell wall development

Vancomycin resistant S. aureus (VRSA)

  • Attributed to plasmid based vancomycin resistance genes for E. faecalis origin
33
Q

Streptocci looks like?

A

chains of balls

34
Q
A

D1 Microbiology (2 decks)

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