MIDTERM 2 - Staphylococcus Flashcards
most important & most commonly encountered organism in medical practice
Genus Staphylococcus
used to distinguish among Gram-positive cocci
Catalase Test
ubiquitous human parasite
Genus Staphylococcus
genus Staphylococcus is catalase-_______-
catalase-positive
30 – 50% colonize skin & mucous membrane of healthy adult & children
Genus Staphylococcus
all pathogenic strains of S. aureus are coagulase _____; whereas nonpathogenic species are coagulase _______
pathogenic= positive
nonpathogenic= negative
genus Streptococcus is catalase-_______
catalase-negative
enzymes that clot blood by a mechanism that is similar to normal clotting
Coagulase Test
also known as clumping factor
bound coagulase - Slide Test
lead to fibrin formation around bacteria, protecting it from phagocytosis
Coagulase
used to distinguish between pathogenic and nonpathogenic members of the genus
Staphylococcus
Coagulase Test
cross-links of fibrinogen in plasma to form fibrin clot that deposits on the cell wall
bound coagulase - Slide Test
individual coccus stick to each other and clumping is observed
bound coagulase - Slide Test
secreted form of beta lactamase; disrupts the beta-lactam portion of penicillin molecule, thereby inactivating the antibiotic
Penicillinase
________ are peptides that are mostly secreted by Gram-positive bacteria.
Exotoxins
= major protein component of cell wall
= major antigenic determinant unique to S. aureus
= protect organism from opsonization and phagocytosis
Protein A
_______ are lipopolysaccharides (LPS) and is secreted by Gram-negative bacteria
Endotoxins
_____ is an extracellular enzyme
free coagulase
Proteins that Disable Host Immune Defenses
Coagulase & Protein A
______ secreted by S.aureus reacts with coagulase reacting factor (CRF) in plasma to form thrombin; converts fibrinogen to fibrin resulting in clotting of plasma
free coagulase
= gram + cocci
= arranged in grape-like clusters
= nonmotile, noncapsulated (mutant strain have capsule & more pathogenic)
= produce lipochrome →golden yellow colonies on blood agar
Staphylococcus aureus
usually affects neonates with local infection of
recently severed umbilicus or older children with skin
infections.
Staphylococcal Scalded Skin Syndrome
also called transpeptidase; necessary for cell wall peptidoglycan formation and is inhibited by penicillin
Penicillin binding protein
diffuse erythematous skin rashes involving entire
body with sloughing off epidermal layer of skin; healing is rapid and mortality low
Staphylococcal Scalded Skin Syndrome
protein that breaks down proteoglycans in connective tissue
Hyaluronidase (“Spreading Factor”)
S. aureus establishes a local infection and releases
Exfoliatin toxin that exerts distant effects
Staphylococcal Scalded Skin Syndrome
enzyme which degrades fats and oils that often accumulate on the surface of our body. This degradation facilitates Staphylococcus aureus’ colonization of sebaceous glands
Lipase
protein that lyses formed fibrin clots
Staphylokinase
destroys tissue proteins
Protease
anti-phagocyti; damage cell membrane of neutrophil & macrophages causing them to lyze; probably help incapacitate the phagocytic line of defense of the host
Leucocidin
no hemolysis; no zones around the colonies
gamma | δ
produce incomplete hemolysis in blood agar; colonies surrounded by a green, opaque zone
alpha | α
causes skin to slough off
(scalded skin syndrome)
Exfoliatin | epidermolytic
produce complete hemolysis in blood agar; clear (transparent) zone surrounding the
colonies
beta | β
cause food poisoning, resulting in vomiting & diarrhea
Enterotoxins (heat stable)
causes toxic shock syndrome; pyrogenic toxins called superantigens and bind to
antigen presenting cells (such as macrophages) causing a massive T cell response and outpouring of cytokines, resulting in the toxic shock syndrome
Toxic Shock Syndrome toxin (TSST-1)
____ is a collection of pus
abscess
deeper infection; tissue becomes hot, red, shiny and
swollen
Cellulitis
2nd leading cause of UTI in sexually active young women
Staphylococcus saprophyticus
S. aureus in food produces ________ not inactivated by cooking
Pre-formed, heat resistant toxin
penetrates vaginal mucosa & is a potent stimulator of tumor necrosis factor (TNF) & interleukin-1
Toxic Shock Syndrome
contagious, occurs on the face honey-colored & wet
Impetigo
_____ is an infection deep into the subcutaneous tissue
furuncle
______ are multiple contiguous, painful lesions
communicating under the skin
carbuncles
most commonly acquired by females (95%) in the
community (NOT in the hospital)
Staphylococcus saprophyticus
white colonies on blood agar; nosocomial & opportunistic infections
Staphylococcus epidermidis
compromised hospital patients with Foley catheters or IV
lines can become infected; frequent skin contaminant of blood cultures
Staphylococcus epidermidis
