Written Exam 3 Slides groups 4 - 7

Question 1

What do staphylococcus look like on a slide?

Answer 1

Staphyl = clusters

Cocci = spheres

Question 2

Is staphylococcus gram + or gram -

Answer 2

Gram +

Question 3

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

Answer 3

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

Question 4

What are the clinically important species of staphylococcus

Answer 4

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

Question 5

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

Answer 5

• 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 (–)

Question 6

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

Answer 6

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

Question 7

Explain Hemolysis on Blood Agar

Answer 7

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

Question 8

Explain how mannitol and halotolerance is used to determine the microorganism

Answer 8

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

Question 9

Describe staphylococcus epidermidis disease overview

Answer 9

• 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

Question 10

Describe the Epidemiology of S. aureus

Answer 10

• 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

Question 11

Explain the Transmission of S. aureus

Answer 11

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

Question 12

Staphylococcus aureus Diseases:

Answer 12

• 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

Question 13

What is an abscess?

Answer 13

• 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

Question 14

What is pyogenic

Answer 14

pus producing abscess

Question 15

Explain abscesses by S. aureus

Answer 15

• 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

Question 16

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

Answer 16

• 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

Question 17

What are virulence factors

Answer 17

• 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

Question 18

What are the major virulence factors of S. aureus?

Answer 18

• 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

Question 19

Answer 19

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

Question 20

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

Answer 20

• 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

Question 21

Cellulitis is what?

Answer 21

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

Question 22

What are the Causes of S. aureus disease

Answer 22

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

Question 23

What is food poisioning?

Answer 23

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

Question 24

What are Toxin Mediated Diseases (name)

Answer 24

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

Question 25

Staphylococcal food poisoning

Answer 25

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

Question 26

Staphylococcal enterotoxin

Answer 26

• 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

Question 27

Toxic Shock Syndrome

Answer 27

• 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

Question 28

Superantigens

Answer 28

• 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

Question 29

Toxic Shock Syndrome

Answer 29

• 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

Question 30

Staphylococcal Scalded Skin Syndrome (SSSS)

Answer 30

• 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

Question 31

Management of staphylococcal infection

Answer 31

• 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)

Question 32

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

Answer 32

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

Question 33

Streptocci looks like?

Answer 33

chains of balls