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Microbio Exam 1 > Staphylococcus > Flashcards

Staphylococcus Flashcards

1
Q

Staphylococcus structure and physiology

A
  • gram positive cocci
  • aerobic
  • catalase positive
  • nonmotile
  • facultative anaerobes
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2
Q

Staph aureus is the only medically important staph species that is ___________.

A
  • coagulase positive

- so a negative coagulase staph means it is not s. aureus

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3
Q

What is coagulase?

A
  • aka clumping factor

- it binds and cleaves fibronogen, converting it to insoluble fibrin which causes S. aureus to clump as a result

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4
Q

S. epidermidis is coagulase ______.

A

-negative

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5
Q

Like GAS, S. aureus expresses many virulence factors with overlapping functions allows for what 3 things?

A
  • attachment
  • evasion of host defenses
  • tissue penetration
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6
Q

Does S. aureus express a capsule? If so, why?

A
  • yes
  • prevents phagocytosis of bacterium by leukocytes and also plays a role in adherence of bacteria to catheters and other synthetic materials
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7
Q

Protein A (Spa): what is it, what does it do, and who has (doesn’t have ) it?

A
  • on surface of most S. aureus strains, but NOT coagulase negative staph
  • binds very tightly to Fc region of antibodies and so prevents antibodies from binding to its antigens and then leading to phagocytosis
  • immune evasion
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8
Q

S. aureus produces many toxins that play a significant role in its virulence. What are some of their effects?

A

-invasive infection, skin exfoliation, food poisoning, TSS

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9
Q

Most toxins in S. aureus are encoded by ______.

A

-plasmids

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10
Q

Alpha toxin: function

A
  • produced by most strains
  • integrates into cell membranes and forms pores
  • Na and Ca flow into cell, water follows, and cell undergoes osmotic lysis
  • important role in tissue damage
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11
Q

Beta toxin: function

A
  • sphingomyelinase enzyme
  • present in most s.aureus strains
  • by cleaving sphingomyelin in membranes of cells, it damages the membrane and can lead to cell lysis
  • plays role in tissue destruction like alpha toxin
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12
Q

Exfoliative toxin

A
  • important in Staph scolded skin syndrome (SSSS)

- proteases that are thought to digest proteins involved in cell to cell contacts

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13
Q

Enterotoxins

A
  • associated with food poisoning and found in 30-50% of staph strains
  • heat stable and resistant to hydrolysis by stomach and intestinal enzymes
  • function as superantigens and nonspecifically activate T cells and cytokine release
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14
Q

What is the issue with enterotoxins begin heat stable?

A

-if food has toxin, you cannot eat it because even if cooked well, toxins will persist

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15
Q

What is thought to cause vomiting that is characteristic of staph food poisoning?

A

-stimulation of mast cell degranulation

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16
Q

Toxic Shock Syndrome Toxin

A
  • very stable toxin
  • superantigen and induces nonspecific and massive release of cytokines that lead to vascular permeability and falling BP
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17
Q

In addition to toxins, Staph can produce a number of enzymes that help it to penetrate tissues and spread. Such as…

A
  • lipases, hemolysins, fibrinolysin, and hyaluronidase

- coagulase

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18
Q

How does coagulase help S. aureus create characteristic infections that S. epidermidis doesn’t?

A

-coagulase helps it bind fibrin and formed walled off abscesses, a major feature of S. aureus infections that S. epidermidis doesnt do

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19
Q

Are coagulase positive or negative Staph more virulent?

A

-positive

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20
Q

Immunity and S. aureus

A

-adaptive immunity is ineffective and so recurrent infection is common

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21
Q

What tests distinguish between S. aureus and S. epidermidis

A

-coagulase and mannitol

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22
Q

T/F: All staphylococci are catalase negative.

A

-False; they are all POSITIVE

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23
Q

Describe s.aureus colonies on agar

A
  • soft, round, convex colonies

- tend to become golden

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24
Q

Main features of S. epidermidis

A
  • common skin flora
  • common contaminant because skin is shed a lot
  • catheter or device-related infections due to biofilm formation
  • UTI
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25
Q

Main features of S. aureus

A
  • predominant nosocomial and community acquired pathogen
  • infection control nemesis
  • commonly carried in human nares and other surfaces
  • numerous virulence factors
  • causes wide spectrum of diseases: local and systemic
  • MRSA
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26
Q

Name virulence factor allowing for Staph aureus to adhere to host cells

A

-clumping factor

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27
Q

Name virulence factors that allow S. aureus to establish infection and evade host defense systems

A
  • Hyaluronidase
  • Protein A
  • TSST-1
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28
Q

Name virulence factors that allow entry of s. aureus into deeper tissue and/or blood

A
  • alpha-hemolysin

- beta-hemolysin

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29
Q

What makes S. aureus so heterogeneous and hard to treat?

A
  • large number of virulence factors

- different strains express different virulence factors

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30
Q

3 patterns of S. aureus carriers

A
  1. persistent carriers (20%)
  2. Intermittent carriers (60%)
  3. Almost never carriers (20%)
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31
Q

What is the primary nosocomial pathogen?

A

-MRSA since hospital antibodies kill off its competition

32
Q

Nosocomial infections are those that occur ________ after admission.

A

-48-72 hours

33
Q

3 categories of disease caused by S. aureus

A
  1. superficial lesions: skin abscesses and wound infections
  2. Systemic and deep-seated/sepsis: pneumonia and bacteremia
  3. Toxin-mediated: toxic shock syndrome and food poisoning
34
Q

Molecular typing technologies have shown that S. aureus infections are largely due to …

A
  • the success and expansion of genetically-related “clones”

- Ex USA300 MRSA

35
Q

Where does S. Aureus most likely colonize?

A

-external nares

36
Q

Food intoxication-heat stable enterotoxins consumed resulting in rapid onset (2-6 hours) of symptoms such as ______________.

A

-emesis and diarrhea

37
Q

Toxins involved in TSS

A

-TSST-1 or exotoxin B or exotoxin C

38
Q

Staphylococcal scalded skin syndrome is a blistering disease caused by what?

A
  • exfoliative toxins A or B (ETA or ETB) that are serine proteases that cause separation of epidermal layers
  • associated with epidemics in nurseries
39
Q

More invasive and disseminated disease (bacteremia, endocarditis, intravenous catheter infection, septic arthritis, osteomyelitis) result when _____________.

A

-tissue barriers are interrupted

40
Q

SSSS primarily affects who?

A

-neonates and young children

41
Q

Progression of SSSS

A
  • abrupt onset; localized erythema often starts around the mouth and eventually can cover the entire body within 2 days
  • skin can slough off as pressure is applied and large blisters form after which the skin desquamates
42
Q

Is scarring an issue in SSSS?

A

-no, because it only impacts epidermis

43
Q

A localized form of SSSS is called _________

A
  • bullous impetigo
  • mostly infants and young children
  • highly communicable, self resolving, localized blisters
44
Q

T/F: like GBS, Staph aureus can cause a superficial crusting infection impetigo.

A

False; GAS and staph aureus can cause this

45
Q

S. aureus causes a number of ________________.

A
  • pyogenic skin infections

- if pus is present in an abscess think staph!!

46
Q

2 types of pyogenic skin infections s. aureus causes

A
  1. folliculitis

2. carbuncles

47
Q

Folliculitis

A
  • infection of hair follicles

- called a stye if at base of eyelid

48
Q

___________ are an extension of folliculitis.

A
  • furuncles (boils)

- large, painful red nodules with dead tissue underneath

49
Q

Carbuncles: what are they and what are they associated with?

A
  • term used when there are multiple furuncles that coalesce

- assoc with fever and chills indicating more severe and systemic infection

50
Q

S. aureus is particularly problematic when skin surface is damaged and organism _____________.

A

-gains access to deeper tissues

51
Q

Where does bacteremia arise from and what is a major complication of it?

A
  • arise from an innocuous skin infection

- endocarditis that is highly fatal due to rapid destruction of heart valves

52
Q

Pneumonia and empyema due to S. aureus

A
  • can occur from aspiration or from hematogenous spread
  • presents like other pneumonias but abscesses and tissue destruction are more common due to array of enzymes produced by staph
53
Q

Bacterial seeding in the blood that is common to S. aureus makes it the most common cause of ….

A

-bone infection, septic arthritis in young children, and intraarticular infections in those with abnormal or artificial joints

54
Q

A common form of food poisoning is due to __________ rather than an infection.

A

-intoxication/ingestion of the toxin

55
Q

What are the most commonly affected foods by S. aureus enterotoxins?

A
  • processed meats
  • potato salad
  • ice cream
56
Q

Contamination to foods by enterotoxin is most commonly due to…

A

-asymptomatic human carrier

57
Q

Once contaminated with S. aureus, what needs to happen for food to become toxin filled?

A
  • needs to be at room temp or higher long enough for the bacteria to grow and release the enterotoxin
  • as the toxin is stable, even if prepared properly, the food is still contaminated
58
Q

Symptoms of staph food poisoning

A

-severe vomiting, nonbloody diarrhea, abdominal pain, nausea

59
Q

What causes TSS?

A

-localized growth of toxin-producing S. aureus producing TSST-1, with release of toxin into blood stream

60
Q

Symptoms of TSS

A
  • abrupt onset
  • fever, hypotension, diffuse macular rash
  • multiple organ failure due to hypotension
  • skin can slough off late in disease
61
Q

How to treat TSS?

A
  • need to treat immediately with antibiotics

- patients who survive (95%) have antibodies to the toxin and are immune

62
Q

S.epidermidis, as a very common colonizer of human skin, is frequently responsible for ___________.

A

-infections involving in-dwelling medical devices

63
Q

Staph epi is a major cause of _______ of artificial heart valves. Where do the infections usually occur and what can happen as a result?

A
  • endocarditis
  • more commonly takes root at sites where valve is sewn into heart which can lead to separation of heart valve at the annulus
  • native valve infections are much less common
64
Q

The presence of an _________________ on staph epi enables efficient attachment to artificial surfaces like catheters and shunts. Why is this such a worrisome issue?

A
  • exopolysaccharide or slime layer
  • indwelling catheters are used extensively especially in debilitated patients
  • such colonization leads to persistent bacteremia and the organisms can be seeded most anywhere else in the body, leading to other localized infections
65
Q

___________ is a significant cause of UTIs in sexually active women.

A

-S. saprophyticus

66
Q

Almost all staph are resistant to _________. So what is used instead?

A
  • penicillin due to acquisition of penicillinases, which hydrolyzes beta lactam ring of penicillin
  • thus the methicillins were used instead but resistance was quickly acquired
67
Q

MRSA acquired an altered PBP that was introduced by a _____________.

A

-phage rendering them resistant to all beta lactam antibiotics

68
Q

Treatment of S. epidermidis

A
  • often depends on removal of foreign body

- vancomycin is drug of choice is necessary

69
Q

MRSA has driven the use of __________ in hospitals, which has contributed to the spread of ________.

A
  • vancomycin

- vancomycin resistance among some other bacteria

70
Q

Methicillin resistance is defined by the presence of ______.

A

mecA gene which encodes for an altered penicillin binding proteins
-harbored on large mobile element

71
Q

CA-MRSA outbreak populations

A
  • sports participants
  • inmates
  • military
  • children in daycare
  • MSM
  • tattoo recipients
  • horse farms
  • crystal meth users
  • native americans, alaskan, pacific islanders
72
Q

HA MRSA vs. CA MRSA

A

-HA: link to healthcare system, multidrug resistant, 5 major genetic backgrounds,SCCmec I,II, III, panton-valentine leukotoxin negative

CA: less resistant, 2 significant clones, SCCmec IV, Panton-valentine leukotoxin +, prone to cause severe pneumonia

73
Q

Resistances of nosocomial MRSA

A

-all beta lactam resistant
->90% resistant to erythromyocin, fluoroquinoline, clinamycin
~50% susceptible to vancomycin

74
Q

Vancomycin Resistant S. aureus (VRSA)

A

-acquired vanA operon like enterococcus

75
Q

VRE: Vancomycin resistant enterococcus risk factors

A
  • prior broad spectrum antibiotics (cephalosporins, vancomycin)
  • prolonged hospitalization
  • immunocompromised host
  • neutropenia
  • admission to an intensive care unit
  • renal failure needing dialysis
76
Q

Since treatment of MRSA is becoming increasingly challenging, how is spread being prevented?

A

-hygiene and infection control

Microbio Exam 1 (13 decks)

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