Chapter 5: Gram-positive Bacteria: Staphylococci Flashcards
0
Q
Staphylococci - Gram stain?
A
Gram-positive
1
Q
What are the 3 major pathogenic species of staphylococci?
A
1) S. aureus
2) S. epidermidis
3) S. saprophyticus
2
Q
Staphylococci - morphology?
A
grape-like clusters of cocci
3
Q
Staphylococci - catalase?
A
catalase-positive
all staph are catalase positive
4
Q
Staphylococcus aureus displays what pattern of hemolysis when grown on blood agar?
A
beta-hemolytic
forms golden pigment on blood agar
5
Q
How can Staphylococcus aureus be differentiated from other beta-hemolytic cocci?
A
S. aureus forms a yellow gold pigment on sheep blood agar (aurei = golden)
6
Q
What beta hemolytic cocci forms yellow gold colonies on blood agar?
A
Staphylococcus aureus
7
Q
Staphylococcus aureus - coagulase?
A
coagulase-positive
8
Q
Which staphylococci species are coagulase positive?
A
Staph aureus
9
Q
Which staphylococci species are coagulase negative?
A
S. epidermidis or S. saprophyticus
10
Q
How can Gram-positive cocci be differentiated from each other?
A
catalase: Staphylococci are positive; Streptococci are negative
11
Q
How can staphylococci species be differentiated from each other?
A
S. aureus is coagulase positive; S. epidermidis and S. saprophyticus are coagulase negative
12
Q
What virulence factors (protective proteins) does Staphylococcus aureus express? (5)
A
1) Protein A
2) Coagulase
3) Hemolysins
4) Leukocidins
5) Penicillinase
13
Q
What is the major virulence factor for Staphylococcus aureus?
A
Protein A
binds the Fc region of IgG to prevent opsonizatin/phagocytosis and complement fixation
14
Q
What is Protein A?
A
binds the Fc portion of IgG to prevent opsonization/phagocytosis and complement fixation
(major virulence factor for Staphylococcus aureus)
15
Q
What protein binds the Fc portion of IgG to prevent opsonization/phagocytosis and complement fixation?
(major virulence factor for Staphylococcus aureus)
A
Protein A
16
Q
Protein A is a major virulence factor for which organism?
A
Staphylococcus aureus
17
Q
What is coagulase?
A
enzyme which activates prothrombin to thrombin, causing blood to clot
18
Q
What enzyme which activates prothrombin to thrombin, causing blood to clot?
(major virulence factor for S. aureus)
A
coagulase
19
Q
How does coagulase act as a virulence factor for Staphylococcus aureus?
A
coagulase, by activating prothrombin, leads to fibrin formation around the bacteria, protecting it from phagocytosis
20
Q
What are hemolysins?
A
enzymes expressed by Staphylococcus aureus that destroy RBCs, neutrophils, macrophages, and platelets. alpha, beta, gamma, and delta types.
21
Q
What enzymes expressed by Staphylococcus aureus destroy RBCs, neutrophils, macrophages, and platelets; and have alpha, beta, gamma, and delta types?
A
hemolysins
22
Q
What are leukocidins?
A
cytotoxin that destroys leukocytes (WBCs), expressed by S. aureus
23
Q
What are cytotoxins that destroy leukocytes (WBCs), expressed by S. aureus?
A
leukocidins
24
Community-acquired methicillin-resistant Staphylococcus aureus (CA-MRSA) produces which particular leukocidin?
Panton-Velentine Leukocidin (PVL)
25
Panton-Valentine Leukocidin (PVL) is produced by which microbe?
CA-MRSA: community-acquired methicillin resistant Stapylococcus aureus
26
What is penicillinase?
secreted form of beta-lactamase, which disrupts the beta-lactam portion of the penicillin molecule, thereby inactivating the antibiotic
27
What enzyme is essentially a secreted form of beta-lactamase, which disrupts the beta-lactam portion of the penicillin molecule, thereby inactivating the antibiotic?
penicillinase
28
What virulence factors (tissue-destroying proteins) does Staphylococcus aureus produce? (3)
1) Hyaluronidase
2) Staphylokinase
3) Lipase
29
What is staphylokinase?
expressed by S. aureus, activates plasmin to break up fibrin clots (like streptokinase)
30
What enzyme, expressed by S. aureus, activates plasmin to break up fibrin clots?
staphylokinase
31
How is lipase a virulence factor for S. aureus?
Lipase degrades fats and oils, which often accumulate on the surface of our body. This degradation facilitates S. aureus' colonization of sebaceous glands.
32
What is hyaluronidase?
breaks down proteoglycans of extracellular matrix. Expressed by Group A strep (S. pyogenes) and S. aureus
33
What protein breaks down proteoglycans of extracellular matrix, and is expressed by Group A strep (S. pyogenes) and S. aureus?
hyaluronidase
34
What superantigen produced by Staphylococcus aureus causes shock?
Toxic shock syndrome toxin (TSST-1)
35
TSST-1 is produced by what microbe and causes what disease?
Staphylococcus aureus; toxic shock
36
How does TSST-1 produced by Staphylococcus aureus produce toxic shock?
TSST-1 superantigens bind to MHC Class II on antigen-presenting cells, causing a massive T cell response (bring MHC II and TCR is close proximity), and subsequent overwhelming release of IFN-g and IL-2.
37
What are the clinical manifestations of toxic shock syndrome? (5)
sudden onset:
1) fever
2) rash (like scarlet fever), diffuse erythematous
3) desquamation late in course of illness
4) nausea, vomiting, watery diarrhea
5) hypotension (septic shock)
38
The sudden onset of the following symptoms is indicative of what syndrome, perhaps caused by what microbe?
1) fever
2) diffuse erythematous rash
3) desquamation of palms and soles
4) nausea, vomiting, watery diarrhea
5) hypotension
toxic shock syndrome, S. aureus
39
What exotoxins are produced by Staphylococcus aureus? (3)
1) Exfoliatin
2) Enterotoxins
3) TSST-1
40
Exfoliatin, enterotoxins, and TSST-1 are exotoxins produced by what microbe?
Staphylococcus aureus
41
What diseases are caused by exotoxin release by Staphylococcus aureus? (3)
1) Gastroenteritis (food poisoning)
2) Toxic shock syndrome
3) Scalded skin syndrome
42
What diseases result from direct organ invasion by Staphylococcus aureus? (8)
1) Pneumonia
2) Meningitis
3) Osteomyelitis
4) Acute bacterial endocarditis
5) Septic arthritis
6) Skin infections: impetigo, cellulitis, abcess/furuncle/carbuncles, wound infections
7) Bacteremia/sepsis
8) Urinary tract infection
43
What causes Staphylococcus aureus related gastroenteritis (food poisoning)?
ingestion of food containing preformed enterotoxin by S. aureus, stimulating peristalsis of the intestine with ensuing vomiting, diarrhea, abdominal pain, and occasionally fever.
44
How long is the incubation period for S. aureus enterotoxin causing food poisoning?
short: 2-6 hr
45
Is the S. aureus enterotoxin causing food poisoning heat stable?
Yes, it is not destroyed by cooking, so it can still cause gastroenteritis
46
Are antibiotics curative in gastroenteritis or toxic shock syndrome caused by S. aureus?
No, because it is the exotoxin, not the bacteria, which causes the clinical manifestations
47
S. aureus TSST-1 causing toxic shock syndrome is classically associated with what?
tampon use
(although infected sutures in surgical wounds, cutaneous and subcutaneous infections, and infections following childbirth or abortion can all be foci from which S. aureus can release TSST-1 exotoxins)
48
Tampon use is classically associated with infection with what microbe?
Staphylococcus aureus
49
Exfoliative toxin A and B produced by S. aureus causes what clinical manifestation?
scalded skin syndrome
50
Scalded skin syndrome is caused by what?
Exfoliatin A and B produced by Staphylococcus aureus
51
What is exfoliatin?
a proteolytic exotoxin that cleaves the desmogleins in desmosomes (middle epidermis), leading to bullous impetigo and SSSS (staphylococcal scalded skin syndrome)
52
Staphylococcal scalded skin syndrome (SSSS) typically affects what population?
neonates, with local infection of the recently severed umbilicus (or older children with skin infections)
53
Which 3 Gram-negative organisms can cause endocarditis?
1) Staphylococcus aureus (acute)
2) S. sanguis (viridans group of Streptococci) (subacute)
3) Enterococcis (Group D streptococci) (subacute)
54
Staphylococcus aureus can cause what type of onset of endocarditis?
acute - sudden onset
55
Streptococci (S. sanguis (viridans) and enterococci) cause what type of onset of endocarditis?
subacute - more gradual onset
56
Do heart valves need to be damaged in endocarditis caused by S. aureus? Or by S. sanguis(viridans) or enterococci?
Acute endocarditis caused by Staphylococcus aureus can happen in a patient with no history of valvular disease and may not have a murmur.
Subacute endocarditis caused by S. sanguis(viridans) or Enterococci tend to be on damaged valves.
57
S. aureus-related subacute endocarditis classically occurs in what population?
IV drug users
58
What is the most common pathogen causing septic arthritis in the pediatric age group and in adults over the age of 50?
Staphylococcus aureus
59
Define impetigo
vesicular blistered eruption that becomes crusty and flaky, frequently found around the mouth
60
What is the term for a vesicular blistered eruption that becomes crusty and flaky, frequently found around the mouth?
Impetigo
61
Define cellulitis.
deep infection of the skin cells, producing red, swollen skin which is hot to the touch
62
What is the term for deep infection of the skin cells, producing red, swollen skin which is hot to the touch?
cellulitis
63
Differentiate between abscesses, furuncles, and carbuncles.
Abscess = collection of pus. Infection of a hair follicle produces a single pus-filled crater with a red rim.
This infection can penetrate deep into the subcutaneous tissue to become a furuncle.
These may bore through to produce multiple contiguous, painful lesions communicating under the skin called carbuncles.
64
Minor skin infections are almost exclusively caused by which microbes?
Streptococcus pyogenes (Group A strep), and Staphylococcus aureus
65
Methicillin resistant Staphylococcus aureus (MRSA) has acquired mecA, a chromosomal DNA segment encoding what?
altered penicillin binding protein that takes over the job of peptidoglycan cell wall assembly when transpeptidase (the normal penicillin binding protein) is inhibited by penicillin (such as methicillin)
66
Vancomycin resistant Staphylococcus aureus (VRSA) has acquired vanA, a chromosomal transposon DNA element that encodes what?
vanA transposon is acquired from vancomycin resistant enterococcus (VRE) that encodes a series of proteins that modify the D-alanine-D-alanine terminus of the peptidoglycan cell wall, changing it to D-alanine-D-lactate, which has a low affinity for vancomycin
67
Panton-Valenine Leukocydin (PVL) toxin is associated with a propensity to form what?
skin abscesses
68
What toxin produced by Staph aureus yields a propensity to form skin abscesses?
Panton-Valentine Leukocidin (PVL) toxin
69
What is the treatment for non-resistant strains of Staphylococcus aureus? (3)
1) Penicillinase-resistant penicillins: nafcillin (IV), dicloxacillin (oral)
2) 1st generation cephalosporins: cefazolin (IV), cephalexin (oral)
3) Clindamycin (IV and oral)
70
What is the treatment for resistant strains of Staphylococcus aureus (MRSA)? (5)
1) Vancomycin (IV)
2) Daptomycin (IV)
3) Clindamycin (IV and oral)
4) Trimethaprim-sulfamethoxazole (IV and oral)
5) Linezolid (IV and oral)
71
Staphylococcus epidermidis - coagulase?
coagulase negative
| S. aureus is the only coagulase positive staphylococcus
72
Staphylococcus epidermidis displays what pattern of hemolysis when grown on blood agar?
```
gamma (non) hemolytic
white colonies (originally named S. albus, where albus means "white")
```
73
Where is Staphylococcus epidermidis normally found?
as part of normal skin flora
74
What microbe frequently contaminates blood cultures?
Staphylococcus epidermidis
| Contamination occurs when the needle used to draw the blood passes through skin covered with S. epidermidis.
75
Staphylococcus epidermidis frequently infects patients where? (2)
1) IV lines or Foley catheters
| 2) prosthetic devices (such as prosthetic joints, prosthetic heart valves, and peritoneal dialysis catheters)
76
What structure allows Staphylococcus epidermidis to bind to prosthetic devices and IV catheters?
biofilm
77
Staphylococcus epidermidis produces biofilm, which gives it what function?
Adhere to and infect prosthetic devices and IV catheters, and protect them from attack by antibiotics and the immune system
78
What is biofilm, and how does it allow Staphylococcus epidermidis to infect prosthetic devices and IV catheters?
Biofilm is an extracellular polysaccharide (glycocalyx) network that forms a mechanical scaffold around bacteria, and allows the bacteria to bind to prosthetic devices, and protects them from attack by antibiotics and the immune system
79
Staphylococcus epidermidis is differentiated from Staphylococcus saprophyticus based on sensitivity to what?
Novobiocin
80
Staphylococcus epidermidis is (sensitive, resistant) to novobiocin.
sensitive
81
What is the treatment for infection with Staphylococcus epidermidis?
Vancomycin
| it is highly resistant to multiple antibiotics
82
Staphylococcus saprophyticus - coagulase?
coagulase-negative
| S. aureus is the only coagulase positive Staph
84
How is Staphylococcus saprophyticus spread?
via bodily fluids
85
Staphylococcus saprophyticus infection often occurs in what population?
sexually active young women
86
How does infection with Staphylococcus saprophyticus typically present?
as cystitis (urinary tract infection):
- dysuria
- polyuria
- abdominal pain/discomfort
87
The first and second most common causes of uncomplicated UTI in sexually active young women are:
1) E. coli
| 2) S. saprophyticus
88
What is the treatment for S. saprophyticus infection?
penicillin
90
Staphylococcus saprophyticus is (sensitive, resistant) to novobiocin.
resistant
