Gram-Positive Cocci

Question 1

Staphylococcus: Genus Characteristics

Answer 1

• Gram-positive cocci
• Grape-like clusters
• Catalase positive

Question 2

Staphylococcus Aureus : Species Characteristics

Answer 2

Coagulase positive • Golden colonies on blood agar • β - hemolytic • Ferments mannitol on mannitol salt agar

Question 3

Staphylococcus Aureus: Reservoir

Answer 3

Normal flora, nose and skin

Question 4

Staphylococcus Aureus : Transmission

Answer 4

• Hands • Sneezing • Surgical wounds • Contaminated food

Question 5

Staphylococcus Aureus: Predisposing Factors

Answer 5

• Breaks in skin • Foreign body • Neutropenia • Intravenous drug abuse • Chronic granulomatous disease • Cystic fibrosis

Question 6

Staphylococcus Aureus : Pathogenic Features

Answer 6

• Coagulase: Converts fibrinogen to fibrin • Alpha Toxin : Pore-forming, cytolytic toxin • Protein A: Inhibits IgG opsonization by binding Fc component • Enterotoxins: Fast acting, heat stable • Toxic Shock Syndrome Toxin-1 (TSST-1): Acts as superantigen • Exfoliatins: Proteases specific for cadherin desmoglein 1, promote epidermal blistering of scalded skin syndrome and bullous impetigo

Question 7

Clinical Syndromes of S. aureus: Food poisoning

Answer 7

3-6 hours onset, salty foods, picnics (ham, canned meats, custard pastries, potato salad) Pathogenesis: Enterotoxlns A·E, preformed In food, heat stable

Question 8

Clinical Syndromes of S. aureus: Infective endocarditis

Answer 8

Acute onset, fever. malaise, leukocytosis, heart murmur Pathogenesis: Coagulase, cytolytic toxins

Question 9

Clinical Syndromes of S. aureus: Pneumonia

Answer 9

Typical pneumonia, salmon·colored sputum, nosocomial, ventilator. postinfluenza, high fatality Pathogenesis: Coagulase, cytolytic toxins

Question 10

Clinical Syndromes of S. aureus: Osteomyelitis (No. 1 cause overall)

Answer 10

Bone Pain, fever, swelling, redness, lytic lesions on imaging Pathogenesis: Coagulase, cytolytic toxins

Question 11

Clinical Syndromes of S. aureus: Surgical Infections

Answer 11

Fever. cellulitis, abscess Pathogenesis: Coagulase, oxfollaUns. TSST

Question 12

Clinical Syndromes of S. aureus: Mastitis

Answer 12

Subcutaneous tenderness, heat, redness Pathogenesis: Coagulase cytolyslns

Question 13

Clinical Syndromes of S. aureus: lmpetigo

Answer 13

Erythematous papules and bullae

Pathogenesis: Coagulase, exfollatlns

Question 14

Clinical Syndromes of S. aureus: Scalded skin syndrome

Answer 14

Dlffuse epidermal peeling

Pathogenesis: Coagulase, exfollatlns

Question 15

Clinical Syndromes of S. aureus: Toxic shock syndrome

Answer 15

Scarlatiniform: rash desquamates, involves palms and soles, fever, hypotension, multi-organ failure Pathogenesis: TSST-1 (superantigen)

Question 16

Treatment of S. aureus

Answer 16

Gastroenteritis: Self -limiting

Nafcillin/oxacillin

Methicillin -resistant Staphylococcus aureus (MRSA): vancomycin

Vancomycin-resistant (VRSA) or vancomycin -intermediate (VISA): Qulnupristin / dalfoprlstin

Question 17

Staphylococcus epidermidis: Species Characteristics

Answer 17

Coagulase-negative Staphylococcus

Gamma hemolytic

Novobiocin sensitive

Question 18

Staphylococcus epidermidis: Pathogenic Features

Answer 18

• Biofilm production

Normal flora of skin

Question 19

Staphylococcus epidermidis: Clinical Syndromes

Answer 19

• Subacute endocarditis in IV drug users

Infections of catheters and prosthetic devices

Question 20

Staphylococcus epidermidis: Treatment

Answer 20

Vancomycin with rifampin or an aminoglycoside

Question 21

Staphylococcus saprophyticus: Species Characteristics

Answer 21

Coagulase-negative Staphylococcus

Gamma hemolytic

Novobiocin resistant

Question 22

Staphylococcus saprophyticus: Clinical Syndromes

Answer 22

Honeymoon cystitis

Question 23

Staphylococcus saprophyticus: Treatment

Answer 23

Quinolones

Question 24

Streptococcus: Genus Characteristics

Answer 24

Gram-positive cocci

Chains or pairs

Catalase negative

Question 25

Streptococcus: Further Classification

Answer 25

The genus Streptococcus Is divided into groups by classification of a cell wall carbohydrate (C carbohydrate). Analysis with this technique separates four medically Important groups: A, B, D, and those that are “ non-groupable” because they lack this carbohydrate. In clinical microbiology, we distinguish the streptococci on the basis of their patterns of hemolysis and associate that result with our knowledge of the four Lancefleld groups.

Question 26

β- Hemolytic Streptococci Group A Streptococcus (GAS; Streptococcus pyogenes): Species Characteristics

Answer 26

β-hemolytic

Bacitracin sensitive

Pyrrolidonyl arylamidase (PYR) positive

Type with M protein

Question 27

β- Hemolytic Streptococci Group A Streptococcus (GAS; Streptococcus pyogenes): Reservoir

Answer 27

Throat and skin

Question 28

β- Hemolytic Streptococci Group A Streptococcus (GAS; Streptococcus pyogenes): Transmission

Answer 28

Respiratory droplets, direct contact

Question 29

β- Hemolytic Streptococci Pathogenic Features of S. pyogenes

Surface features: Pili and teichoic acids

Answer 29

Question 30

β- Hemolytic Streptococci Pathogenic Features of S. pyogenes:

Soluble secretions

Answer 30

Question 31

β- Hemolytic Streptococci Pathogenic Features of S. pyogenes:

Spreading factors

Answer 31