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Staphylococci Flashcards

1
Q

True or False: Micrococci are usually associated with disease and are considered clinically significant when isolated from human specimens.

A

False: Micrococci are not typically associated with disease and not considered clinically significant when isolated from human specimens

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2
Q

Staphylococci are usually recovered from the ______ _______ or as commensals inhabiting the ________ and _______ ______.

A

Staphylococci are usually recovered from the external environment or as commensals inhabiting the skin and mucous membranes.

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3
Q

Staphylococcus aureus is commonly found in the ______ ______ of 20 - 40% of adults, as well as the _________, __________, _________.

A

Staphylococcus aureus is commonly found in the anterior nares of 20 - 40% of adults, as well as the Perineum, Axillae, Vagina.

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4
Q

In general, Staph aureus most commonly infects sites where the organism is ______________.

A

Sites where the organism is a part of the normal flora.

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5
Q

Specifically, what sites on the body are most commonly infected by Staph aureus? (Name them)

A

Skin , nose/throat, GI tract, urethra, vagina

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6
Q

What general conditions are caused by S. aureus skin infection?

A

Furuncles, carbuncles, folliculitis, cellulitis

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7
Q

Describe the cause and implications of a furuncle:

A

A skin disease caused by infection of the hair follicle that results in localized accumulation of pus and dead tissue.

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8
Q

Describe the appearance of a furuncle, include:

  • Color?
  • Tender?
  • Temperature?
  • Purulent?
  • Pain?
A

Furuncle Appearance:

  • Red, pus-filled lumps that are tender, warm, and extremely painful
  • A yellow or white point at center of lump can be seen when boil is ready to drain
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9
Q

Define a carbuncle:

A

An abscess larger than a boil, usually with one or more openings draining pus onto the skin

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10
Q

Most common sites of carbuncles?

A

May develop anywhere, but are most common on the back and the nape of the neck

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11
Q

What are the 4 general virulence factors of S. aureus?

A
  1. Adhesin (Protein A)
  2. Lysins (Hemolysins)
  3. Enzymes “-ases”
  4. Cytotoxins
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12
Q

Describe the function of Protein A as a driver of virulence for S. aureus.

A

Protein A on the surface of Staph aureus organisms binds the Fc region of the antibody so that it is no longer recognized by the phagocyte, preventing opsonization and phagocytosis of S. aureus by PMNs

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13
Q

Describe the function of each hemolysin as a driver of virulence for S. aureus. (4 types)

A

Lysins lyse RBCs and leukocytes

α-hemolysin: Pore former; most closely associated with tissue damage

β-hemolysin: Sphingomyelinase

Gamma-hemolysin: Pore former

Delta-hemolysin: Surfactant that disrupts cell membranes

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14
Q

Describe the function of enzymes (“-ases”) as a driver of virulence for S. aureus. (4 types)

A

Each of these enzymes assists in cell to cell spread

Coagulase – conversion of fibrinogen to fibrin to form a clot

Fibrinolysin - breaks down fibrin clots

Hyaluronidase - hydrolyzes intercellular matrix connective tissue

Lipase – survival in sebaceous material

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15
Q

What are the 3 cytotoxins that drive virulence for S. aureus.

A

Exfoliatins or Exfoliative Toxins

Enterotoxins

Superantigen: Toxic shock syndrome toxin-1 (TSST-1)

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16
Q

Describe the function of Exfoliatins as a driver of virulence for S. aureus.

A

Exfoliatins or Exfoliative Toxins

  • Dissolves the mucopolysaccharide matrix of epidermis
  • Causes separation of skin layers
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17
Q

Describe Enterotoxins as a driver of virulence for S. aureus.

A

Enterotoxins

  • Heat-stable toxin that causes food poisoning
  • Not produced by ingested Staphylococcus
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18
Q

What 5 factors predispose an individual to S. aureus infection?

A
  1. Congenital or acquired defects in leukocyte chemotaxis
  2. Defects in opsonization by antibodies
  3. Defects in intracellular killing of bacteria following phagocytosis
  4. Skin injuries
  5. Presence of foreign bodies
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19
Q

List severe disease syndromes in which Staphylococcus aureus should be considered in the differential diagnosis.

A

Septic arthritis and osteomyelitis

Sepsis syndrome

Necrotizing pneumonia

Necrotizing fasciitis

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20
Q

Who is affected in staphylococcal scalded skin syndrome?

A

Neonates and young children

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21
Q

What are the 4 hallmark clinical manifestations of staphylococcal scalded skin syndrome?

A

No bacteria or leukocytes are present in the fluid

Erythema spreads from around mouth to cover entire body

Large cutaneous bullae (blisters) form followed by sloughing off of the skin layer (desquamation of the epithelium)

Bullae contain clear fluid

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22
Q

What S. aureus virulence factors cause scalded skin syndrome?

A

Exfoliatins or Exfoliative Toxins

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23
Q

What are the hallmark clinical manifestations of staphylococcal food poisoning?

A

Severe vomiting, nausea, diarrhea, abdominal cramping, headache, but not fever

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24
Q

True or False: Staphylococcal food poisoning is caused when an individual ingests Staph aureus. Explain.

A

False: Staphylococcal food poisoning is caused by intoxication with a Staph toxin, but not infection by the organism.

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25
Q

True or False: To determine the organism that causes Staph food poisoning, it is good to culture the organism from the food.

A

False. It is unlikely to recover the organism from the food. Cell culture would not be helpful in this case.

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26
Q

Incubation period for staph aureus food poisoning?

A

Very rapid, 4 hour incubation period

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27
Q

Foods associated with Staph aureus food poisoning?

A

Associated with processed meats, custard-filled pastries, potato salad, ice cream

28
Q

What virulence factor(s) are responsible for Staphylococcal food poisoning?

A

Enterotoxins

29
Q

True or False: Heating food will prevent Staphylococcal food poisoning.

A

False. Enterotoxins in the food are heat-labile. Heating may kill the organism, but the toxin will cause symptoms.

30
Q

What are the 6 hallmark clinical manifestations of Staphylococcal Toxic Shock Syndrome?

A

Multi-organ toxicity

Febrile and hypotensive

Diffuse erythematous rash over entire body

Disseminated intravascular coagulation (DIC) and severe thrombocytopenia

Entire skin desquamates

Vomitting and watery diarrhea

31
Q

Population in which Staphylococcal Toxic Shock Syndrome is usually observed?

A

Often observed in young women using tampons

32
Q

What virulence factor(s) are responsible for Staphylococcal Toxic Shock Syndrome?

A

Toxic shock syndrome toxin-1 (TSST-1)

33
Q

How does Toxic shock syndrome toxin-1 (TSST-1) cause disease?

A

It is a super-antigen that causes non-specific activation of T-cells (MHC class II), followed by polyclonal T-cell proliferation, and massive cytokine release.

34
Q

What are the 2 hallmark clinical manifestations of Staphylococcal cellulitis/abscess? Required inoculum?

A

Large, pyogenic lesions surrounded by erythema

Pain, edema, and accumulation of purulent material

High inoculum required in immunocompetent host

35
Q

What event(s) are typically responsible for the onset of Staphylococcal cellulitis/abscess?

A

Staphylococcal cellulitis/abscess often occurs following trauma or introduction of a foreign body

36
Q

Which staphylococcal species is most likely associated with acute urinary tract infection in young women?

A

Staphylococcus saprophyticus

37
Q

What is the 2nd most common cause of uncomplicated cystitis (after E. coli) among women of college and child-bearing age?

A

Staphylococcus saprophyticus

38
Q

How is Staphylococcus saprophyticus differentiated from other Staph species?

A

Identification of Staphylococcus saprophyticus is based on a negative coagulase test and resistance to novobiocin

39
Q

Name 3 ways Staphylococcus lugdunensis is differentiated from other Staph species.

A

Colonizes human inguinal area

More virulent than other coagulase-negative Staph

Most commonly associated with native-valve, prosthetic-valve, and pacemaker-associated endocarditis

40
Q

What are the hallmark clinical manifestations of Native Valve Endocarditis caused by Staphylococcus lugdunensis?

A

Acute onset weakness of right extremity

10 weeks of fever, chills, malaise, shortness of breath

tachycardia, hypotension, fever, pansystolic murmur

Multiple positive blood cultures

41
Q

Name 2 ways Staphylococcus epidermidis is differentiated from other Staph species.

A

Most often associated with infections of indwelling devices (i.e. catheters)

Biofilm production

42
Q

Describe the virulence mechanism of Staphylococcus epidermidis.

A

Virulence is related to production of extracellular slime that promotes adherence to surfaces of foreign bodies forming biofilm. The biofilm protects S. epidermidis from antimicrobial agents.

43
Q

Hemolysis of S. aureus?

A

beta-hemolytic - Complete hemolysis of the RBC

44
Q

Morphology of S. aureus?

A

Golden beta-hemolytic colonies

Gram positive cocci in clusters

45
Q

Name4 tests for lab identification of S. aureus.

A

Beta Hemolysis on blood agar

Mannitol Salt Agar

CHROMagar

Coagulase test

46
Q

S. aureus result on Mannitol Salt agar?

A

Organisms are salt tolerant and use mannitol as a sugar/energy source

47
Q

S. aureus result on CHROMagar?

A

Turns organism a characteristic color that identifies it

48
Q

Describe the “slide coagulation” technique via latex agglutination assay.

A

Fibrinogen is attached to a small bead that contains a monoclonal antibody to protein A. The beads act by binding protein A and interacting with coagulase (converts fibrinogen to fibrin) on the surface of S. aureus to cause agglutination. Only occurs if the organism is coagulase positive.

49
Q

Methicillin Resistant Staphylococcus aureus (MRSA) is responsible for __________ and ___________ Staph infections.

A

Methicillin Resistant Staphylococcus aureus (MRSA) is responsible for hospital-associated and community-associated Staph infection

50
Q

Methicillin Resistant Staphylococcus aureus (MRSA) is resistant to all ____________ antibiotics.

A

Methicillin Resistant Staphylococcus aureus (MRSA) is resistant to all beta-lactam antibiotics.

51
Q

What confers methicillin resistance to Staph aureus?

A

The mecA Gene

52
Q

What is the mechanism of resistance conferred by mecA?

A

mecA encodes for altered “penicillin-binding protein 2a” (PBP2a), which alters the cell wall such that beta-lactam antibiotics no longer have binding affinity at penicillin-binding proteins. Thus, peptidoglycan synthesis proceeds even in the presence of antibiotics

53
Q

How is mecA acquired?

A

mecA is carried on a mobile genetic element called “staphylococcal cassette chromosome mec” (SCCmec)

54
Q

2 groups that are most susceptible to MRSA Infections?

A

Patients in hospitals and healthcare facilities

Patients who have weakened immune systems

55
Q

In hospitals, the most important reservoirs of MRSA are _________________.

A

In hospitals, the most important reservoirs of MRSA are colonized or infected patients

56
Q

Both __________ and _________ patients contaminate the hospital environment with MRSA at the same relative frequency

A

Both infected and colonized patients contaminate hospital environment with MRSA at the same relative frequency

57
Q

How does septic arthritis and osteomyelitis present?

A

spider-bite cellulitis
pain and fever
joints feel like “jelly”

58
Q

How does cellulitis progress to septic arthritis and osteomyelitis?

A

Hematogenous dissemination or secondary infection

59
Q

Groups outside of the hospital that are at risk of MRSA?

A 
MPSM
MSM
Correctional inhabitants
Military Recruits
Daycares and nurseries
60
Q

Staph aureus: catalase

A

Catalase positive (bubbling reaction)

61
Q

Staphylococci: morphology

A

Gram-positive Cocci in clusters

62
Q

Staphylococci: media

A

Grows in minimal media

63
Q

Staphylococci: oxygen requirement

A

Prefers an aerobic environment

64
Q

Name the catalase negative Staph organisms:

A

Staph saprophyticus, epidemidis, and ludunensis

65
Q

First step in resolving an S. epidermidis infection?

A

Removal of infected foreign bodies

Bacteria (15 decks)

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