Pathology of Infections II

Question 1

describe staphylococci

Answer 1

• G+ve positive cocci in clumps
• normally colonize human skin
• 3 common species:
  
  • S. aureus, S. epidermidis, S. saprophyticus
• can produce 2 types of lesion:
  
  • inflammatory
  • toxin-mediated

Question 2

most infections of the staphylococci species are caused by ___

Answer 2

most infections of the staphylococci species are caused by S. aureus

Question 3

describe inflammatory lesions of staphylococci

Answer 3

• skin:
  
  • folliculitis, furuncle, carbuncle, cellulitis, impetigo, abscess paronychia and surgical wound infection
• postpartum mastitis
• bacteremia
• endocarditis:
  
  • tricuspid valve: common in IV addicts
• osteomyelitis
  
  • organisms reach bone hematogenously or directly from adjacent abscesses or through traumatic implantation
• pneumonia:
  
  • bronchopneumonia, abscess, empyema
• bacteremia abscesses: lung, kidney, brain
• 80% penicillin resistant (MRSA)

Question 4

describe impetigo and risk factors for it

Answer 4

superficial skin infection, highly contagious

• risk factors: crowding, DM, poor nutrition

Question 5

describe etiology of impetigo

Answer 5

• etiology:
  
  • Staph aureus
  • Streptococcus pyogenes

Question 6

describe clinical features of impetigo

Answer 6

• clinical features:
  
  • rash usually begins on face
  • vesicles and pustules rupture to form honey-colored crusted lesions

Question 7

describe complications of impetigo

Answer 7

• cellulitis, septicemia, scarlet fever (rare)

Question 8

describe a furuncle, and risk factors and diagnosis of it

Answer 8

• skin abscess
  
  • common on neck, face, buttocks and armpit
• involve hair follicle and surrounding tissue
• risk factors: diabetes, obesity, immunocompromised, crowding with poor hygiene
• diagnosis: clinical, swab for culture and sensitivity

Question 9

Answer 9

Question 10

describe what is seen in the image

Answer 10

Question 11

describe what is seen in the image

Answer 11

Question 12

describe what is seen in the image

Answer 12

Question 13

describe lung abscesses and risk factors and clinical features

Answer 13

localized area of superficial necrosis within the lung

• risk factor: aspiration of gastric contents, bronchial obstruction, endocarditis, dental extraction
• clinical features: cough productive of foul-smelling sputum, fever and finger clubbing

Question 14

describe a chest x-ray of lung abscesses

Answer 14

• intrapulmonary cavity with irregular air-fluid level

Question 15

describe what is seen in the image

Answer 15

Question 16

describe what is seen in the image

Answer 16

Question 17

describe the toxin-mediated lesions of staphylococci

Answer 17

Question 18

describe the pathogenesis of toxic shock syndrome

Answer 18

• associated with the use of intra-vaginal tampon and other risk factors (skin wound, recent surgery)
• if left longer, leads to growth of Staph → release of exotoxin (super antigen) → stimulate polyclonal T cell activation which induces T cells to release high levels of cyotkines → diffuse rash, vasodilation, hypotension and death

Question 19

describe clinical features and diagnosis of toxic shock syndrome

Answer 19

• clinical features: fever, hypotension, vomiting, diarrhea, skin erythema, confusion, rash resembling a sunburn especially on palms and soles
• diagnosis: blood culture, cervical swabs

Question 20

describe streptococci

Answer 20

• G+ve cocci
• present in pairs or chains
• species: S. pyogenes, S. pneumoniae, S. agalactiae viridans group and enterococcus
• produce hemolysis

Question 21

_____ is the most important human pathogen (streptococci)

Answer 21

Group A beta hemolytic is the most important human pathogen (streptococci)

Question 22

describe direct, exotoxin and indirect damage by streptococci

Answer 22

• direct damage:
  
  • suppurative - cellulitis, abscess, pneumonia
• exotoxin mediated
  
  • Scarlet fever
• indirect damage by immune responses
  
  • Rheumatic heart disease/glomerulonephritis

Question 23

describe streptococcus pneumonia (aka pneumococcal pneumonia) and risk factors, clinical features and investigations of it

Answer 23

• causes lobar pneumonia
• G+ve lancet-shaped diplococci, most common cause of community-acquired pneumonia
• healthy young adults
• risk factors: diabetes, CHF, COPD, absent spleen
• clinical features: fever, productive cough, chest pain, bloody sputum, dullness to percussion (consolidation), bronchial breath sounds, late inspiratory crackles
• investigations: CXR (gold standard), blood/sputum culture, neutrophilic leukocytosis

Question 24

describe the pathology of streptococci pneumonia

Answer 24

• bronchioles and alveolar walls are not damaged
• spreads through the pores of Kohn to involve the entire lobe
• it passes through different stages:
  
  • congestion: exudates rich in fibrin, RBC, a few PMN
  • red hepatization: exudates consist of RBCs, fibrin, more PMNs
    
    • lung loses its spongy consistency, feels solid and red like a liver
  • grey hepatization: congestion and fibrin disappear, PMNs replaced by macrophages
  • resolution: macrophages clear up the debris a few days later

Question 25

describe outcomes of streptococcus pneumonia

Answer 25

• antibiotics alter of halt the typical progression
• most patients show a total resolution in 10 days
• complications are rare and include:
  
  • lung abscesses
  • fibrosis (organization)
  • empyema

Question 26

describe what is seen in the image

Answer 26

Question 27

describe what is seen in the image

Answer 27

Question 28

describe bronchopneumonia

Answer 28

• patchy involvement of lung; usually bilateral
• begins as an acute bronchitis, spreads locally into the lungs
• unlike lobar pneumonia, there is destruction of bronchioles and alveoli
• common in the young, elderly and bed ridden
• caused by: hemophilus influenzae, Klebsiella (alcoholic), Pseudomonas aeruginosa (CF) and staphylococci (post viral URTI), streptococci
• may lead to abscess formation, empyema and bacteremic dissemination

Question 29

Answer 29