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Flashcards in Staphylococcus Deck (76):
1

Staphylococcus structure and physiology

-gram positive cocci
-aerobic
-catalase positive
-nonmotile
-facultative anaerobes

2

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

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

3

What is coagulase?

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

4

S. epidermidis is coagulase ______.

-negative

5

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

-attachment
-evasion of host defenses
-tissue penetration

6

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

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

7

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

-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

8

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

-invasive infection, skin exfoliation, food poisoning, TSS

9

Most toxins in S. aureus are encoded by ______.

-plasmids

10

Alpha toxin: function

-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

11

Beta toxin: function

-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

12

Exfoliative toxin

-important in Staph scolded skin syndrome (SSSS)
-proteases that are thought to digest proteins involved in cell to cell contacts

13

Enterotoxins

-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

14

What is the issue with enterotoxins begin heat stable?

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

15

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

-stimulation of mast cell degranulation

16

Toxic Shock Syndrome Toxin

-very stable toxin
-superantigen and induces nonspecific and massive release of cytokines that lead to vascular permeability and falling BP

17

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

-lipases, hemolysins, fibrinolysin, and hyaluronidase
-coagulase

18

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

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

19

Are coagulase positive or negative Staph more virulent?

-positive

20

Immunity and S. aureus

-adaptive immunity is ineffective and so recurrent infection is common

21

What tests distinguish between S. aureus and S. epidermidis

-coagulase and mannitol

22

T/F: All staphylococci are catalase negative.

-False; they are all POSITIVE

23

Describe s.aureus colonies on agar

-soft, round, convex colonies
-tend to become golden

24

Main features of S. epidermidis

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

25

Main features of S. aureus

-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

26

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

-clumping factor

27

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

-Hyaluronidase
-Protein A
-TSST-1

28

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

-alpha-hemolysin
-beta-hemolysin

29

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

-large number of virulence factors
-different strains express different virulence factors

30

3 patterns of S. aureus carriers

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

31

What is the primary nosocomial pathogen?

-MRSA since hospital antibodies kill off its competition

32

Nosocomial infections are those that occur ________ after admission.

-48-72 hours

33

3 categories of disease caused by S. aureus

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

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

-the success and expansion of genetically-related "clones"
-Ex USA300 MRSA

35

Where does S. Aureus most likely colonize?

-external nares

36

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

-emesis and diarrhea

37

Toxins involved in TSS

-TSST-1 or exotoxin B or exotoxin C

38

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

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

39

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

-tissue barriers are interrupted

40

SSSS primarily affects who?

-neonates and young children

41

Progression of SSSS

-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

Is scarring an issue in SSSS?

-no, because it only impacts epidermis

43

A localized form of SSSS is called _________

-bullous impetigo
-mostly infants and young children
-highly communicable, self resolving, localized blisters

44

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

False; GAS and staph aureus can cause this

45

S. aureus causes a number of ________________.

-pyogenic skin infections
-if pus is present in an abscess think staph!!

46

2 types of pyogenic skin infections s. aureus causes

1. folliculitis
2. carbuncles

47

Folliculitis

-infection of hair follicles
-called a stye if at base of eyelid

48

___________ are an extension of folliculitis.

-furuncles (boils)
-large, painful red nodules with dead tissue underneath

49

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

-term used when there are multiple furuncles that coalesce
-assoc with fever and chills indicating more severe and systemic infection

50

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

-gains access to deeper tissues

51

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

-arise from an innocuous skin infection
-endocarditis that is highly fatal due to rapid destruction of heart valves

52

Pneumonia and empyema due to S. aureus

-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

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

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

54

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

-intoxication/ingestion of the toxin

55

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

-processed meats
-potato salad
-ice cream

56

Contamination to foods by enterotoxin is most commonly due to...

-asymptomatic human carrier

57

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

-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

Symptoms of staph food poisoning

-severe vomiting, nonbloody diarrhea, abdominal pain, nausea

59

What causes TSS?

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

60

Symptoms of TSS

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

61

How to treat TSS?

-need to treat immediately with antibiotics
-patients who survive (95%) have antibodies to the toxin and are immune

62

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

-infections involving in-dwelling medical devices

63

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

-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

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

-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

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

-S. saprophyticus

66

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

-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

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

-phage rendering them resistant to all beta lactam antibiotics

68

Treatment of S. epidermidis

-often depends on removal of foreign body
-vancomycin is drug of choice is necessary

69

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

-vancomycin
-vancomycin resistance among some other bacteria

70

Methicillin resistance is defined by the presence of ______.

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

71

CA-MRSA outbreak populations

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

72

HA MRSA vs. CA MRSA

-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

Resistances of nosocomial MRSA

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

74

Vancomycin Resistant S. aureus (VRSA)

-acquired vanA operon like enterococcus

75

VRE: Vancomycin resistant enterococcus risk factors

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

76

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

-hygiene and infection control