Chapter 5: Staphylococci Flashcards
What are the three major pathogenic species of Staphylococci?
Staph aureus, epidermidis, and saprophyticus
What are the three tests that can differentiate Staphylococci from streptococci?
Gram stain
Catalase test
Culture
How does staph compare to strep in a gram stain?
Staph are in clusters with a golden appearance (aureus)
Strep are found in a line like candy buttons
How does staph compare to strep in a catalase test?
All staphylococci have catalase
Rub wire loop across a colony of gram-positive cocci and mix on a slide with H2O2
Bubbles = catalase
Strep does NOT have catalase
How does Staph compare to Strep in a culture?
Staph aureus can be differentiated from other beta-hemolytic strep by its golden pigment on sheep blood agar
What is the ONLY Staphylococcus that is coagulase positive? what does this mean?
Staphylococcus aureus
Activates prothrombin causing blood to clot
Leads to fibrin formation around the bacteria
What proteins of Staphylococcus aureus disable our immune system?
Protein A Coagulase Hemolysins Leukocidins Penicillinase Novel penicillin binding protein/transpeptidase
What does Protein A do?
Site that binds to Fc portion of IgG
May protect the organism from opsonization and phagocytosis
What is the role of hemolysins?
4 types - alpha, beta, gamma and delta
Destroy RBC, neutrophils, Mo and platelets
What is the role of leukocidins?
destroy leukocytes (WBCs)
What particular leukocidin does CA-MRSA produce?
Panton-Valentine Leukocidin (PVL) - associated with a propensity to form abscesses
What is Novel penicillin binding protein?
Necessary for cell wall peptidoglycan formation and is inhibited by penicillin
What proteins released by Staphylococcus aureus tunnel through tissue?
Hyaluronidase: breaks down proteoglycans in CT
Staphylokinase: lyses formed fibrin clots
Lipase: Degrades fats and oils
Protease: destroys tissue proteins
What protein facilitates Staphylococcus aureus’ colonization of sebaceous glands?
Lipase
What is the exotoxin assault weaponry of Staphylococcus aureus?
Exfoliatin
Enterotoxins
TSST-1
What is the role of exfoliatin?
Diffusible exotoxin that causes skin to slough off
Scalded skin syndrome
Toxic Shock Syndrome Toxin
Analogous to the pyrogenic toxin produced by Lancefield Group A beta-hemolytic streptococci, but far more deadly
Bind MHC class II molecules on APCs, causes T cell response and outpouring of cytokines
What are the diseases caused by exotoxin release from Staphylococcus aureus ?
Gastroenteritis (food poisoning): growth in food, peristalsis of the intestine leading to nausea, vomiting, diarrhea, abdominal pain, and fever 12-24 hrs
TSS: tampons, stimulate TNF and IL-1
Scalded skin syndrome: Exfoliative toxin A and B, localized infection and releases diffusible toxin that exerts distant effects,
Who does Scalded Skin Syndrome mostly affect?
Describe what clinically happens
Neonates with local infection of the recently severed umbilicus or older children with skin infections
Causes cleavage of the middle epidermis with fine sheets of skin peeling off to reveal moist red skin beneath
Healing rapid
What are the diseases resulting from direct organ invasion of Staphlycoccus aureus?
Pneumonia Meningitis Osteomyelitis Acute bacterial endocarditis Septic arthritis Skin infections Bacteremia/sepsis Urinary tract infection
Staphylococcus aureus and pneumonia
Rare but severe cause of CA-bacterial pneumonia
More common in hospitalized pts
Usually follows viral flu
Abrupt onset of fever, chills, and lobar consolidation of the lung, rapid destruction of the lung parenchyma
Effusions and empyema
Osteomyelitis
bone infection that usually occurs in boys under 12 yrs of age
Infection spreads to the bone hematogenously,
Warm, swollen tissue over the bone and with systemic fever and shakes
Caused by Staph aureus
What is the most common pathogen causing Septic arthritis in pediatric age group and in adults over the age of 50
Staph Aureus
Minor skin infections are almost exclusively caused by what?
Either Strep pyogenes or Staph aureus
