Staphylococcus and Streptococcus

Question 1

Staphylococcus

Answer 1

• 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

Question 2

Pathology depends on

Answer 2

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

Question 3

Alpha toxin

Answer 3

genome and plasmid

Question 4

B toxin

Answer 4

shingomyelinase C

Question 5

Gamma toxin

Answer 5

detergent like action

Question 6

Y toxin

Answer 6

cell lysis

-S and F pore formation

Question 7

Exfoliative toxins

Answer 7

Staphylococcal scalded skin syndrome SSSS

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

Question 8

Enterotoxins

Answer 8

• contaminated food

- stable to healing, gastric enzymes

Question 9

Toxic Shock Syndrome Toxin-1 (TSS-1)

Answer 9

• can penetrate mucosal barriers (systemic infection)

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

Question 10

Staphylococcal enzymes

Answer 10

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

Question 11

Spread

Answer 11

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

Question 12

Staphylococcal Scalded Skin Syndrome SSSS

Answer 12

• 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

Question 13

Staphylococcal food poisoning

Answer 13

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

Question 14

Toxic schock syndrome

Answer 14

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

Question 15

Cutaneous infections (pyogenic)

Answer 15

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

Question 16

Pneumonia

Answer 16

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

Question 17

Osteomyelitis and septic arthritis

Answer 17

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

Question 18

Septic arthritis

Answer 18

-painful, red joints, pus present on aspiration

Question 19

Staphylococcus epidermis

Answer 19

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

Question 20

Staphylococcus saprophyticus

Answer 20

• urinary track infections (UTIs)

- coagulase-negative

Question 21

Identification of S. aureus

Answer 21

B hemolytic: sheep blood agar (rings)

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

Question 22

Identification of S. epidermis

Answer 22

Non-hemolytic: sheep blood agar

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

Question 23

Antibiotic therapy

Answer 23

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

Question 24

Vancomycin resistance

Answer 24

• 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

Question 25

Streptococcus

Answer 25

- gram positive - facultative anaerobes - chains or pairs - catalase negative

Question 26

Hemolysis on sheep blood agar *alpha*

Answer 26

partially hemolysis, green color

Question 27

Hemolysis on sheep blood agar *beta*

Answer 27

complete clearing around the colony

Question 28

Hemolysis on sheep blood agar *gamma*

Answer 28

No color change, no hemolysis

Question 29

Hemolysis and streptococcus

Answer 29

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

Question 30

S. pyogenes

Answer 30

- 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)

Question 31

S. pyogenes toxins and enzymes

Answer 31

- 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

Question 32

Steptokinase (A and B)

Answer 32

- 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

Question 33

DNases A-D

Answer 33

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

Question 34

Pharyngitis (strep throat)

Answer 34

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

Question 35

Pyoderma (impetigo)

Answer 35

- 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

Question 36

Erysipels

Answer 36

- accute skin infection | - pain infamation, lymph nodes enlarged, systemic signs (fever, chills, leukocytosis)

Question 37

Cellulitis

Answer 37

- skin and deeper subcutaneus tissues - hard to tell infected from uninfected skin - local inflamation systemic signs

Question 38

Acute stage of eryspelas

Answer 38

- erythma *redness* | - bullae *blisters*

Question 39

Necrotizing fasciitis

Answer 39

- deep on subcutaneus tissue - extensive destruction of muscle, fat - introduced through break in skin - toxicity multiorgan failure, death

Question 40

Rheumatic fever

Answer 40

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

Question 41

Acute glomerulonephritis

Answer 41

- occur after pharyngeal or pyodermal strep | - acute inflammation of renal glomeruli: edema hypertension, hematuria, protein in both blood and urine

Question 42

Laboratory diagnosis S. pyogenes

Answer 42

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

Question 43

culture on blood agar + antibiotics PHARYNGITIS

Answer 43

swab tonsils

Question 44

culture on blood agar + antibiotics IMPETIGO

Answer 44

pus from a closed lesion

Question 45

culture on blood agar + antibiotics NECROTIZING FASCIITIS

Answer 45

blood tissues

Question 46

culture on blood agar + antibiotics ERYSIPELAS and CELLULITIS

Answer 46

not useful

Question 47

PYR test

Answer 47

+: red color | -: white no color change

Question 48

Treatment, prevention control S. pyogenes

Answer 48

- 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

Question 49

S. pneumoniae

Answer 49

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

Question 50

Diagnosis S. pneumoniae

Answer 50

- spinal fluid - direct gram stain - detection of capsular antigen - optochin sensitive

Question 51

Treatment prevention contral S. pneumoniae

Answer 51

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