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MICR 3343 > Staphylococcus and Streptococcus > Flashcards

Staphylococcus and Streptococcus Flashcards

1
Q

Staphylococcus

A
  • one of the most opportunistic infections in hospitals
  • gram stain purple
  • grapes
  • facultative anaerobes
  • grow in high salt
  • catalase positive
  • skin, soft tissues, bones, urinary track
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2
Q

Pathology depends on

A
  • production of surface proteins that mediate adherence to host tissues
  • secretion of extracellular toxins
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3
Q

Alpha toxin

A

genome and plasmid

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4
Q

B toxin

A

shingomyelinase C

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5
Q

Gamma toxin

A

detergent like action

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6
Q

Y toxin

A

cell lysis

-S and F pore formation

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7
Q

Exfoliative toxins

A

Staphylococcal scalded skin syndrome SSSS

  • mostly in young children
  • produced by 5-10% of S aureus
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8
Q

Enterotoxins

A
  • contaminated food

- stable to healing, gastric enzymes

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9
Q

Toxic Shock Syndrome Toxin-1 (TSS-1)

A
  • can penetrate mucosal barriers (systemic infection)

- death by hypovolemic shock (leads to multi-organ failure)

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10
Q

Staphylococcal enzymes

A
  • coagulase (fibrinogen) cells clump
  • Hyaluronidase (hydrolyzes connective tissue)
  • Fibrinolysin (dissolve fibrin clots)
  • Lipases (hydrolyze lipids) ensure survival of fatty tissue
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11
Q

Spread

A
  • tissue-degrading enzymes (lipase) cutaneous, subcutaneous tissues
  • hyaluronidase (connective tissue)
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12
Q

Staphylococcal Scalded Skin Syndrome SSSS

A
  • young children
  • localized erythema (redness/inflammation) starts around mouth, covers entire body in 2 days
  • large blisters
  • skin peels
  • mortality rate is low
  • Bullous impetigo is a localized form
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13
Q

Staphylococcal food poisoning

A
  • not an infection
  • food contaminated by humans
  • recovery occur within hours
  • symptoms: vomiting, nausea, diarrhea, abdominal pain
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14
Q

Toxic schock syndrome

A
  • fever, hypotension, rash
  • desquamation, vomiting, diarrhea
  • organs involved: CNS, GI, hematologic, hepatic, muscles and renal
  • mortality 5%
  • high rate of occurrence
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15
Q

Cutaneous infections (pyogenic)

A
  • impetigo (pus filled vesicles, dry crusted lesions)
  • folliculitis
  • furuncles (bolis)
  • carbuncles (require surgical drainage and antibiotics)
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16
Q

Pneumonia

A
  • aspiration of oral secretions
  • very young, elderly, chronically ill
  • patchy infiltrates, abscesses
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17
Q

Osteomyelitis and septic arthritis

A
  • dissemination to bone, secondary infection, or migration from adjacent site
  • localized pain, high fever
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18
Q

Septic arthritis

A

-painful, red joints, pus present on aspiration

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19
Q

Staphylococcus epidermis

A
  • major component of skin flora
  • opportunistic infection
  • noncomial infection
  • endocarditis - native heart valves
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20
Q

Staphylococcus saprophyticus

A
  • urinary track infections (UTIs)

- coagulase-negative

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21
Q

Identification of S. aureus

A

B hemolytic: sheep blood agar (rings)

  • yellow pigmented (aureus)
  • coagulase positive
  • Mannitol fermentation
22
Q

Identification of S. epidermis

A

Non-hemolytic: sheep blood agar

  • non-pigmented
  • does not ferment mannitol
  • coagulase negative
23
Q

Antibiotic therapy

A
  • Resistant to penicillin (penicillinase)
  • B-lactam antibiotics (often ineffective, modified penicillin binding proteins)
  • Vancomycin (current drug of choice, resistance has been observed)
24
Q

Vancomycin resistance

A
  • Low level: thicker, more disorganized cell wall, drug may be trapped in cell wall; unable to reach membrane
  • High level uncommon: vanA gene operon from enterococci, modified peptidoglycan layer cant bind vancomycin
25
Q

Streptococcus

A
  • gram positive
  • facultative anaerobes
  • chains or pairs
  • catalase negative
26
Q

Hemolysis on sheep blood agar alpha

A

partially hemolysis, green color

27
Q

Hemolysis on sheep blood agar beta

A

complete clearing around the colony

28
Q

Hemolysis on sheep blood agar gamma

A

No color change, no hemolysis

29
Q

Hemolysis and streptococcus

A
  • Groups A and B (beta)
  • Group D (alpha or gamma)
  • S. pneumoniae and viridans (alpha)
30
Q

S. pyogenes

A
  • avoids phagocytosis (hyaluronic acid capsule), inactivate complement cascade C3b, C5a
  • adheres to surface of host cell by 10 dff antigens
  • invades epithelial cells (M and F proteins)
31
Q

S. pyogenes toxins and enzymes

A
  • heat-labile toxins SpeA, SpeB, SpeC, SpeF
  • act as super antigens: TH cells enhanced release proinflamatory cytokines
  • Streptolysin S : B-hemolyses
  • Streptolysin O: oxigen labile, inhibited by cholesterol in skin infections
32
Q

Steptokinase (A and B)

A
  • rapid spread in tissues
  • cleave plasminogen to plasmid, which cleaves fibrin and fibrinogen resulting in lysis of blood clots and fibrin deposits
  • alpha-spreptokinase antibodies useful markers for infection
33
Q

DNases A-D

A
  • breakdown of free DNA in pus
  • reduces viscosity, facilitates spread
  • alpha-DNase B antibodies an important maker for skin infection
34
Q

Pharyngitis (strep throat)

A
  • 2-4 day after exposure
  • sore throat, fever, malaise, headache
  • red posterioir pharynx with exudate pus
  • Scarlet fever due to pyrogenic exotoxin
35
Q

Pyoderma (impetigo)

A
  • skin infection
  • direct contact with an infected person
  • enters to break in skin
  • blisters form, fill with pus, break, crust over
  • regional lymph nodes enlarge
36
Q

Erysipels

A
  • accute skin infection

- pain infamation, lymph nodes enlarged, systemic signs (fever, chills, leukocytosis)

37
Q

Cellulitis

A
  • skin and deeper subcutaneus tissues
  • hard to tell infected from uninfected skin
  • local inflamation systemic signs
38
Q

Acute stage of eryspelas

A
  • erythma redness

- bullae blisters

39
Q

Necrotizing fasciitis

A
  • deep on subcutaneus tissue
  • extensive destruction of muscle, fat
  • introduced through break in skin
  • toxicity multiorgan failure, death
40
Q

Rheumatic fever

A
  • can occur after pharyngeal strep only
  • inflammatory changes in heart, joints, blood vessels, subcutaneous tissue
  • specific class IM protein types
41
Q

Acute glomerulonephritis

A
  • occur after pharyngeal or pyodermal strep

- acute inflammation of renal glomeruli: edema hypertension, hematuria, protein in both blood and urine

42
Q

Laboratory diagnosis S. pyogenes

A
  • microscopy: Gram + cocci, pairs or chains, associated with leukocytes
  • Antigen detection: group specific carbohydrate in throat swab
43
Q

culture on blood agar + antibiotics PHARYNGITIS

A

swab tonsils

44
Q

culture on blood agar + antibiotics IMPETIGO

A

pus from a closed lesion

45
Q

culture on blood agar + antibiotics NECROTIZING FASCIITIS

A

blood tissues

46
Q

culture on blood agar + antibiotics ERYSIPELAS and CELLULITIS

A

not useful

47
Q

PYR test

A

+: red color

-: white no color change

48
Q

Treatment, prevention control S. pyogenes

A
  • penicillin (oral cephalosporin if allergic to pen)
  • oxacillin or vancomycin id S. aureus is also present
  • can prevent rheumatic fever
  • resistant to tetracyclines, sulfonamides, erythromycin, macrolides
49
Q

S. pneumoniae

A
  • alpha hemolytic
  • pneumolysin (degrades red blood cells under aerobic conditions)
  • grows well on sheep blood agar
  • no group antogen
50
Q

Diagnosis S. pneumoniae

A
  • spinal fluid
  • direct gram stain
  • detection of capsular antigen
  • optochin sensitive
51
Q

Treatment prevention contral S. pneumoniae

A
  • levofloxacin or vancomycin-ceftriaxone
  • resistance to penicillin, erythromycin, tetracycline, cephalosporins
  • anticapsular vaccin prevention
  • 23 different capsule polysaccharies

MICR 3343 (10 decks)

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