Staphylococcus Flashcards
What are the 6 major characteristics of species in the genus Staphylococcus?
- G+ cocci arranged in grape-like clusters
- facultative anaerobe
- non-motile (non-flagellated)
- non-spore forming
- catalase positive (can break down and detoxify H2O2)
- grow on media containing high salt
What are the 2 widely used culture media for Staphylococcus?
- Mannitol salt agar containing high salt concentrations (6.5-10%)
- Blood agar
What 4 Gram-positive bacteria are able to grow on Mannitol salt agar? What 2 bacteria are selected against?
- Staphylococcus
- Enterococcus
- Listeria
- Micrococcaceae
- Gram-negative bacteria
- Streptococcus
What 2 species of Staphylococcus can be differentiated on Mannitol salt agar?
- S. aureus is able to ferment the mannitol, which causes the agar to change from a red to yellow color
- S. epidermidis is not able to ferment mannitol, so there is no color change
Staphylococcus on purple agar base:
What is the purpose of blood agar in Staphylococcus identification? What 3 classifications can be made?
differentiates between the type of hemolysis toxin produced
- α = incomplete hemolysis, gree
- β = complete hemolysis, clear
- γ = no hemolysis, no change in media
What causes β-hemolyzing Staphylococcus to turn blood agar yellow? Give an example of a β-hemolyzing and and γ-hemolyzing Staphylococcus species.
the presence/production of the golden-colored carotenoid, staphyloxanthin (antioxidant)
β = S. aureus
γ = S. epidermidis
What 3 ways should Staphylococcus infections be diagnosed?
- Gram stain: shape/stain color
- biochemical tests: hemolysis, catalase, coagulase
- molecular biology: PCR of nuc gene
How should Staphylococcus test in catalase tests?
positive - they have catalase that is able to break down H2O2
What tests aid in genus identification of Staphylococcus? Species/pathogenicity?
- Gram stain
- catalase test
- coagulase test
- blood agar growth
Coagulase test:
Which strains of Staphylococcus are most pathogenic? Why?
coagulase-positive, especially those with β-hemolysis
can clot hosts serum and lyse RBCs
(S. aureus, S. schleiferi, S. pseudointermedius, S. delphini)
Staphylococcus can be found in the normal microflora of many species. When do they become dangerous?
OPPORTUNISTIC PATHOGEN - if the host is in unfavorable circumstances causing stress or depression of the immune system, the bacteria is able to cause disease
In what 2 places are Staphylococcus normally found in animals?
- skin
- tubular orifices (nasal cavity, buccal cavity, nasopharynx, mammary glands, groin)
What are the 3 major risk factors of Staphylococcal diseases?
- linked to parasitic (tick, sarcoptic mange, lice), fungi (Mycotoxin), and viral (Parvovirus, Poxvirus) infections
- shearing sheep/grooming damages skin and can disrupt the normal barriers that keep Staphylococcus out
- nutritional imbalances, like zinc and vitamin deficiencies
What are the 3 broad virulence factors for pathogenicity in Staphylococcus?
- body structures for adhesion and binding
- enzymes
- toxins
What are the 4 body structures for adhesion and binding in Staphylococcus?
- cell wall - bacterial viability, homeostasis, protection from attack by host lysozyme
- protein A - binds Fc of IgG to block immune response and opsonization
- binding or clamping factors - attachment to host proteins
- capsule (slime layer) - useful for adhesion, preventing chemotaxis, and inhibiting phagocytosis by polymorphonuclear leukocytes
What 7 enzymes are present in Staphylococcus to increase their virulence?
- hyaluronidase - breaks down connective tissue between adjacent cells to let the bacteria dig deeper between cells
- catalase - protects against host reactive oxygen species
- coagulase - clots blood to hide in it
- staphylokinase - lyses clots to come out and disperse itself
- lipase - digests lipids, allowing it to colonize skin surface and sebaceous glands
- protease - destroys tissue proteins
- β-lactamase - inactivates β-lactams to survive treatment
What 5 toxins contribute to Staphylococcus virulence?
- hemolysin - destroys RBCs, neutrophils, macrophages, and platelets
- cytolytic toxins (leukocidin) - destroy cell membranes of host cells (leukocytes)
- exfoliative toxin - separates skin layers, resulting in impetigo and peeling
- toxic shock syndrome (TSS) toxin - causes shock and superantigens (mass T cell activation)
- enterotoxins - cause food poisoning by stimulating gut motility and superantigens
What are the 6 steps in Staphylococcal pathogenesis?
- entry of 100s of Staphylococci by breaching body barriers
- adhesion and attachment on the host cell surface or to a matrix between each cell
- biofilm formation on the host cell surface for persistence
- advance into intracellular invasion, multiplication, and persistence within host cells
- elicit inflammation, abscess formation, necrosis, and bacterial encapsulation
- bacteria will either hide in dormant small colony variants (SCVs) or the abscess containing them will mature, rupture, and cause bacterial spread
What does abscess rupture tend to lead to? What organs are most affected?
bacteremia, followed by diverse organ infection
those with high cardiac output - endocardium, lung, meninges, liver, kidney, uterus, bones, joints
Metastasis of Staphylococcus in the blood is dependent on what 2 things?
- serotype of Staphylococcus
- immune status
What are 4 coagulase-positive species of Staphylococcus? 3 coagulase-negative?
- S. aureus —> mammals and birds
- S. hyicus —> pigs
- S. pseudointermedius —> pigs
- S. schleiferi —> pets
- S. chromogenes —> mammals
- S. felis —> pets
- S. epidermidis —> humans
How does S. epidermidis cause foot odor in humans?
isovaleric acid production following degradation of leucine in sweat by bacterial leucine dehydrogenase
