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Musculoskeletal > Microbiology: skin infection agents > Flashcards

Microbiology: skin infection agents Flashcards

1
Q

what are two examples of resident skin bacteria?

A

Gram positive Staphylococcus epidermis and Propionibacterium acnes

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2
Q

what are two examples of transient skin bacteria?

A

Staphylococcus aureus and Streptococcus pyogenes

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3
Q

what is impetigo?

A

a bacterial infection by Group A strep and/or staph; it results in intraepidermal vesicles with exudate in them

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4
Q

what is erysipelas?

A

it is a more severe bacterial skin infection that involves dermal and lymphatic invasion and is often caused by group A streptococci - it is characterized by tender erythematous lesions

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5
Q

what is cellulitis?

A

bacterial infections that target subcutaneous fat layers and often develop into septicemia or lymphangitis
caused by Group A strep or Staphylococcus aureus

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6
Q

what is folliculitis?

A

it is an abscess caused by staphylococcus aureus around a hair follicle - a pruritic eruption

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7
Q

what is a boil?

A

enlarged folliculitis

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8
Q

what is a carbuncle?

A

a clustering of boils

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9
Q

what are general features of abscesses?

A
  1. neutrophil infiltration
  2. lysosomal enzyme release
  3. fibrin deposition to form capsule to sequester the abscess
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10
Q

what is fasciitis?

A

bacterial infection spreading down superficial fascia, destroying vessels and nerves, leading to patchy necrosis and cutaneous anesthesia
often caused by Group A streptococci

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11
Q

what is gas gangrene?

A

myonecrosis - caused by gas-producing bacteria like CLostridium

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12
Q

what are the bacteria that cause folliculitis?

A

staphylococci, pseudomonas

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13
Q

what are the bacteria that cause folliculitis?

A

staphylococci

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14
Q

what are the bacteria that cause impetigo?

A

strep and staph

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15
Q

what are the bacteria that cause impetigo?

A

strep

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16
Q

what are the bacteria that cause cellulitis?

A

strep, staph, haemophilus influenza type B

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17
Q

what are the bacteria that cause gas gangrene?

A

clostridia

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18
Q

what are the bacteria that cause necrotizing fascitis?

A

streptococci, enteric bacteria, anaerobes

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19
Q

general characteristics of streptococci?

A

catalase negative, GM +, PYR +, facultative anaerobes

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20
Q

alpha hemolytic?

A

greenish, partial hemolysis

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21
Q

beta hemolytic?

A

yellowish/clear, complete hemolysis

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22
Q

gamma hemolysis?

A

no hemolysis, nothing

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23
Q

group A streptococci characteristics?

A

GM+, beta-hemolytic, catalase negative, bacitracin sensitive

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24
Q

what are some group A strep virulence factors?

A

M protein, hyaluronic acid capsules, pyrogenic exotoxins, streptolysin O, DNases, Streptokinase, C5a peptidase

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25
Q

what is M protein

A

it is a coiled coil fibril that is covalently bound to cell wall

  1. it prevents phagocytosis
  2. aids in adhesion to epithelium
  3. binds fibrinogen and therefore prevents complement deposition
  4. has a hypervariable region to which antibodies will be different to
  5. mimics proteins on the surface of the heart - so can be dangerous
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26
Q

what is a hyaluronic capsule?

A

it has the same component as human connective tissues so it acts as camouflage

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27
Q

what are some pyrogenic exotoxins?

A

they are often encoded by phages

  1. superantigens that activate T cells systemically and cause release of INF-gamma and TNF-alpha causing septic shock and multi-organ failure
  2. scarlet fever:streptococcal pyrogenic exotoxin A, B, C
  3. toxic shock syndrome
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28
Q

what is streptolysin O?

A

an exotoxin that is oxygen labile and that is hemolytic - can be very toxic to some cells

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29
Q

what are DNases?

A

used to degrade/denature cell-free DNA in purulent lesions; also work against NETs

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30
Q

what is streptokinase?

A

it lyses blood clots, helping bacteria spread

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31
Q

what is C5a peptidase?

A

it degrades the C5a complement preventing neutrophil chemotaxis

32
Q

what are some suppurative group A streptococcal diseases?

A

pharyngitis, pyoderma, streptococcal toxic shock syndrome

33
Q

what is pharyngitis?

A

it is the inflammation of the oropharynx, accompanied by petechiae on the soft palate

34
Q

what is pyoderma?

A

impetigo, erysipelas, fasciitis, cellulitis, may be caused by pyrogenic exotoxin A and cysteine proteases

35
Q

what is streptococcal toxic shock syndrome?

A

pyrogenic exotoxins released that cause bacteremia and necrotizing fasciitis

36
Q

what are the non-suppurative group A strep diseases?

A

rheumatic fever, and acute poststreptococcal glomerulonephritis

37
Q

what is rheumatic fever?

A

occurs after strep throat and can lead to carditis, polyarthritis, and chorea
can be due to M protein anitbody cross reacting with heart tissue and is a huge risk for valvular disease
pateints require long term penicillin

38
Q

acute poststreptococcal glomerulonephritis

A

depositoin of antibody/antigen complexes on glormeruli after throat or skin infection of strep

39
Q

what is PANDAS syndrome?

A

“pediatric autoimmune neurpsychiatric disorder associated with group A streptococci” - OCD/tic disorder, pediatric onset, GAS infections associated, neurologic abnormalities like motor hyperactivity, choreiform movements

40
Q

what are the best treatments for Group A streptococcal infections?

A

penicillin G, oral cephalosporins; if have a co-infection with staph, use penicillinase

41
Q

what are the results of a blood agar and coagulase test for Staphylococcus epidermis?

A

negative coagulase test, non-hemolytic on blood agar

42
Q

what are the results of a blood agar and coagulase test for Staphylococcus aureus?

A

positive coagulase test, beta-hemolytic on blood agar

43
Q

what are some general characteristics of Staph?

A

GM+, catalase positive, facultative anaerobes, variable coagulase test, variable hemolysis

44
Q

what test would you use to differentiate between Staph and Strep?

A

catalase - staph is catalase positive, strep is catalase negative

45
Q

how woud you differentiate between S. aureus and S. epidermis?

A

use a coagulase test - aureus would be positive

or a hemolysis test, aureus would be beta hemolytic

46
Q

what does the coagulase test entail?

A

add prothrombin to bacterial mixture, fibrinogen converted to fibrin, make clots!

47
Q

what is the hallmark of Staph. aureus infections?

A

pus! suppurative lesions

48
Q

what is hydradentis suppurative?

A

infection of sweat glands

49
Q

what are some risk factors for skin infections by staph?

A

diabetes, acne, wet conditions, poor hygiene

50
Q

what are some risk factors for wound infections via staph?

A

steroid therapy, obesity, diabetes, malnutrition, prolonged surgery, foreign body (like catheter)

51
Q

what are the two major invasive infection types caused by staph aureus?

A

deep lesions and bacteremia

52
Q

what are deep lesions and wht kind of diseases can they cause?

A

they are metastatic abscesses that cause deeper infections than the location of the primary infection - can cause osteomyelitis, septic arthritis, meningitis, pneumonia

53
Q

what is bacteremia?

A

spread of bacteria into blood - a typically sterile environment; can lead to septic shock, septicemia, meningitis, pneumonia, pyelonephritis, endocarditis

54
Q

what are the virulence factors for staph aureus?

A

protein A, catalase, leukocidin, ribotechoic and techoic acid, coagulase, capsule, hyaluronidase, cytotoxins

55
Q

what is protein A?

A

a virulence factor in Staph aureus that binds to the Fc portion of anitbodies, pushing the Fab portion away, preventing it binding to antigen and also occupying the Fc portion preventing phagocyte binding

56
Q

what is catalase?

A

a staph aureus virulence factor that prevents damage from free radicals secreted by neutrophils

57
Q

what is leukocidin?

A

a staph aureus virulence factor that damages neutrophils

58
Q

what are ribotechoic and techoic acids?

A

they are staph aureus virulence factors that bind fibronectin as well as cause septic shock (due to their similarity to G- endotoxin)

59
Q

what is coagulase?

A

a staph aureus virulence factor - it is an enzyme that causes clotting (fibrinogen to fibrin)

60
Q

what is the function of the staph aureus capsule?

A

preventing phagocytosis - a virulence factor

61
Q

what is hyaluronidase?

A

a staph aureus virulence factor that degrades hyaluronic acid in allows navigation into subcutaneous layers

62
Q

what is alpha-hemolysin?

A

a pore-forming cytotoxin

63
Q

what is beta-toxin?

A

(aka sphingomyelinase C) it hydrolyzes membrane phospholipids

64
Q

what is delta toxin?

A

it is cytolytic - acts like a detergent

65
Q

what do gamma toxin and panton-vanlentine leukocidin do?

A

they are pore-forming in neutrophils and macrophages

66
Q

what are some examples of staph toxin mediated diseases?

A

exfoliative diseases, toxic shock, food poisoning

67
Q

what are staph exfoliative diseases?

A

they are caused by staph exfoliatin A, B which are tissue specific serine proteases that cause separation of the epidermis at the desmosomes

68
Q

what are some examples of exfoliative diseases caused by staph?

A

bollus impetigo, staph scarlet fever, scalded skin syndrome

69
Q

what is the toxin that causes staph toxic shock syndrome?

A

toxic shock syndrome toxin-1

70
Q

what are the toxins that cause staph food poisoning?

A

staphylococcal enterotoxins A-E

71
Q

two lab methods useful for tracking staph?

A

pulsed field gel electrophoresis (restriction enzymes) and phage tracking

72
Q

what is another name for methicillin?

A

semi-synthetic penicillin

73
Q

what do we call bacteria that are sensitive to methicillin?

A

MSSA - methicillin sensitive staph aureus

74
Q

what do some S. aureus have that makes them resistant to penicillin?

A

beta-lactamase

75
Q

what do we call baceria resistant to methicillin and what do we kill them with?

A

MRSA - methicillin resistant staph aureus; we treat with vancomycin

76
Q

what do S. epidermidis cause?

A

osteomyelitis, endocarditis, UTIs, infections of indwelling foreign devices (like catheters, stents, pacemakers - biofilms can form)

Musculoskeletal (21 decks)

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