micro 2

Question 1

s. aureus history

Answer 1

b hemolysis , catalse +, coagulase +, protein A virulance factor
colonize the nares, ears, axilla groin

Question 2

s. aureus infections

Answer 2

1. Localized skin infections: The most common S. aureus infections are small, superficial abscesses involving hair follicles (folliculitis) or sweat or sebaceous glands, Furuncles, carbuncles Wound infection (traumatic, surgical) Cellulitis Impetig
2. . Deep, localized infections: These may be metastatic from superficial infections or skin carriage or may result from trauma. S. aureus is the most common cause of acute and chronic infection of bone marrow. S. aureus is also the most common cause of acute infection of joint space in children (septic joint)
3. Acute endocarditis: Generally associated with intravenous drug abuse
4. Septicemia is a generalized infection with sepsis or bacteremia that may be associated with a known focus (for example, a septic joint) or not (an occult focus).
5. Pneumonia: S. aureus is a cause of severe, necrotizing pneumonia.
6. Nosocomial infections: S. aureus is one of the most common causes of hospital-associated infections, often of wounds (surgical, decubital) or bacteremia associated with catheters (see Figure 8.10). Progression to septicemia is often a terminal event.

Question 3

S. Aureus Toxinoses

Answer 3

a. Toxic shock syndrome: TSS results in high fever, rash (resembling a sunburn, with diffuse erythema followed by desquamation), vomiting, diarrhea, hypotension, and multiorgan involvement (especially GI, renal, and/or hepatic damage
b. Staphylococcal gastroenteritis: This is caused by ingestion of food contaminated with enterotoxin-producing S. aureus.
c. Scalded skin syndrome: This involves the appearance of superficial bullae resulting from the action of an exfoliative toxin that attacks the intercellular adhesive of the stratum granulosum, causing marked epithelial desquamation (see Figure 8.12). The bullae may be infected or may result from toxin produced by organisms infecting a different site.

Question 4

s. epidermidis

Answer 4

• flora of the skin
• causes contamination of specimens
• invade the prosthetic devices and joint
• form bio-film adhere to the surfaces and shelter the bacteria from the antibiotics

Question 5

Staphylococcus saprophyticus

Answer 5

Gram ⊕, catalase ⊕, coagulase ⊝, urease ⊕ cocci in clusters. Novobiocin resistant. Normal flora of female genital tract and perineum. Second most common cause of uncomplicated UTI in young women (most common is E coli).

Question 6

Streptococcus pneumoniae

Answer 6

Gram ⊕ , lancet-shaped diplococci A . Encapsulated. IgA protease. Optochin sensitive. Most common cause of:

ƒ .Meningitis ƒ
.Otitis media (in children) ƒ
.Pneumonia ƒ
.Sinusitis

Pneumococcus is associated with “rusty” sputum, sepsis in patients with sickle cell disease, and asplenic patients.

No virulence without capsule.

MOPS commonly spread pneumonia.

Question 7

Viridans group streptococci

Answer 7

Normal flora of the oropharynx.

Streptococcus mutans and S mitis cause dental caries.

S sanguinis makes dextrans that bind to fibrin-platelet aggregates on damaged heart valves, causing subacute bacterial endocarditis.

Question 8

Streptococcus pyogenes (group A streptococci)
Disease

Answer 8

cause:

ƒ 😗Pyogenic—pharyngitis, cellulitis, impetigo (“honey-crusted” lesions), erysipelas ƒ
😗Toxigenic—scarlet fever, toxic shock–like syndrome, necrotizing fasciitis ƒ
😗Immunologic—rheumatic fever, glomerulonephritis

Question 9

Streptococcus pyogenes (group A streptococci)

Answer 9

Pharyngitis can result in rheumatic “phever” and glomerulonephritis.

Strains causing impetigo can induce glomerulonephritis.

Scarlet fever—blanching, sandpaper-like body rash, strawberry tongue, and circumoral pallor in the setting of group A streptococcal pharyngitis (erythrogenic toxin ⊕ ).