Staphylococci Flashcards
Staphylococcus is a Gram _____ organism
Gram positive
What test is used to differentiate staph. from strep.?
Catalase test
Stain –> Gram + –> Catalase test –> Positive –> Staph
Species of staph are differentiated based on their production of _____
Coagulase
What is/are the coagulase positive staph(?) The coagulase negatives?
Positive: Staph aureus
Negative: Staph epidermidis/saprophyticus
T/F: S. aureus ferments mannitol
TRUE
On mannitol salt agar, S. aureus ferments mannitol, turning it red to yellow.
Which virulence factor of S. aureus binds the Fc region of IgG, preventing opsonization/phagocytosis. Which other factor aids in immunoevasion?
Protein A binds Fc of IgG
Microcapsule also helps in immunoevasion
Which virulence factor of S. aureus helps it to invade/spread?
Invasins (hyaluronidase, staphylysin, leukocidin, leukotoxin, coagulase, staphylokinase)
Which virulence factor(s) of S. aureus functions as fibronectin adhesins? As vitronectin adhesins? As collagen adhesins?
Fibronectin adhesins: Fb3 and Embp
Vitronectin adhesins: AtlE
Collagen adhesins: GehD
What virulence factors of S. aureus are superantigens?
TSST, EFT, & SE A-G (enterotoxin)
What happens after S. aureus adherence?
Replication/secretion of exotoxins (TSST, EFT, SE-AG)
What are the hemolysins secreted by S. aureus?
Alpha-toxin, gamma-toxin, phenol soluble modulins
Which two virulence factors of S. aureus aid in biofilm formation?
PIA (polysaccharide interellular adhesin) & Aap (Accumulated associated protein)
A _____ is a collection of pus usually around a hair follicle. Tx?
Abscess
Tx: Incise, drain, surgically remove foreign body. Usually no abx given.
A _____ is an abscess into subQ tissue. Tx?
Furuncle
Incise, drain, DOXYCYCLINE, mupirocin to nares, bleach baths
A _____ consists of multiple contiguous furuncles. Tx?
Carbuncle
Drainage +/- abx therapy depending on severity
On blood agar, S. aureus forms a _____ colony, with possible hemolysis.
Grey/gold colony
Which S. aureus virulence factor causes tissue damage @ the site of infection?
Hemolysins
Alpha-toxin, e.g. is the major pore forming toxin that causes skin necrosis during S. aureus infection
Staph aureus is the lading cause of _____ wound infections
Nosocomial wound infections (particularly coronary bypass wounds)
Which two products of S. aureus help it spread along fascial planes, causing cellulitis?
Staphylokinase + hyaluronidase
What is the opthalmologic emergency staph aureus can cause? What is its clinical presentation?
Corneal ulceration (via alpha/beta/delta/gamma toxins, coagulase, nuclease, lipase, hyaluronidase)
Presentation: Stromal cellular infiltration (pus) + anterior chamber reaction
_____ is a skin disorder caused by S. aureus that appears as honey-colored/flaky lesions on the face and around the mouth.
Impetigo
Staph aureus can cause food poisoning after consumption of _____ products.
Dairy products/mayo.
In Staph aureus food poisoning, staph enterotoxin stimulates _____ in the stomach.
Vagus nerve endings
_____ is a condition caused by S. aureus where the skin is lifted and filled with fluid. What is the pathogenesis of this condition?
Scalded Skin Syndrome
S. aureus secretes epidermolytic exotoxins (exfoliatin A and B), proteases that destroy desmoglein-1. This causes detachment within the epidermal layer.
Scalded Skin Syndrome is characterized by what three clinical symptoms?
Fever, large bullae, erythematous macular rash.
What are two potential complications of Scalded Skin Syndrome?
Secondary infection due to large areas of exposed flesh
Electrolyte imbalance from exudation of serous fluid
_____ is a condition caused when S. aureus colonize a tampon, sponge or wound and secrete large amounts of TSST-1. This compound is absorbed and acts as a super-antigen. What are some symptoms of this condition?
Toxic Shock Syndrome
Sx: Fever, nausea, vomiting, diarrhea followed by rash and exfoliation. May progress to multiple organ system failure like septic shock.
Describe the “Trojan Horse” mechanism of dissemination of S. aureus.
S. aureus hijacks a neutrophil during phagocytosis. Inside, it won’t be effectively killed by abx.
After hijacking a neutrophil, S. aureus can move to the heart or bone and cause what two conditions?
Heart: Infective endocarditis (inflammation of valves/congenital defects)
Bone: Osteomyelitis
Which Staphylococci cause acute infective endocarditis? Chronic?
Acute: S. aureus
Chronic: Coagulase negative staph
Which toxin secreted by S. aureus forms pores in cells that line the alveolar space, allowing fluid to accumulate inside of the tissue?
Panton Valentine Leukocidin (PVL)
PVL activates _____, causing _____ release. What do these activated cells do?
PVL activates PMNs and macrophages causing IL-8 release.
Activated cells go on to destroy the cells lining the alveolar space –> hemorrhage
Reminder: IL-8 (CXCL8) is a chemokine that recruits neutrophils to the tissue.
T/F S. epidermidis is coagulase-negative and ferments mannitol.
FALSE
While S. epidermidis is coagulase negative, is does NOT ferment mannitol.
T/F S. saprophyticus is not known to cause any human disease.
FALSE
S. saprophyticus is the second most common cause of UTI
How is S. saprophyticus UTI treated?
Amoxicillin or Bactrim/sulfa-trimethoprim
Which species of Staphylococcus is known for its resistance to Novobiocin?
S. saprophyticus
Which species of Staphylococcus are coagulase negative and do not ferment mannitol?
S. epidermidis & S. saprophyticus
S. epidermidis produces a lot of adhesins and proteins that make it stick to plastic. What kind of patients are susceptible to eperdimidis because of this feature?
Patients in the ICU (lots of lines, plastic, etc.)
