Lec4 Staphylococci Flashcards
What is shape of staphylococci?
- pram positive
- cocci
What distinguishes streptococci from staphylococci?
- staphylococci are catalase positive
- staph grows in clusters, strep grows in pairs/chains
How can staphylococcus aureus be distinguished?
- gram positive coccus
- forms clusters [rather than chains]
- coagulase positive
Is staphylococcus aureus coagulase negative or positive?
positive
What are the virulence factors of staphylococcus aureus?
- growth as biofilm
- surface factors
- secreted proteins [exotoxins]
What is action of surface factors of staphylococcus aureus?
- 6 surface proteins
- facilitate binding to collagen, fibronectin, ferritin
- they are adhesion factors
What is action of secreted proteins of staphylococcus aureus?
- 5 cytotoxins and 12 enzymes
- facilitate hemolysis and spread of infection
What is the role of protein A in staphylococcus aureus?
- protein A is a virulence factor present in most strains, correlated with virulence
- bind Fc terminal of IgG –> inhibits complement and phagocytosis
- increases ability to cause inflammatory diseases [skin infection, organ abscess, pneumonia, endocarditis
What is role of capsule in staphylococcus aureus?
- polysaccharide capsule surrounds organism
- prevent opsonization
What are two staphylococal proteins that act as superantigens?
- staphylococcal enterotoxin
- TSST-1
lead to toxic shock
What does staphylococcal release of alpha toxin do?
cause septic shock
Are staphylocci typically pyogenic or non-pyogenic?
pyogenic - means they form lots of pus
Are coagulase positive or coagulase negative strains of staphylococci more virulent?
coagulase positive [s. aureus] are more virulent
What are 3 toxin mediated mechanisms of staph aureus [including disease and which related toxin]?
toxic shock syndrome [TSST-1 toxin]
scalded skin syndrome [exfoliative toxin]
rapid onset food poisoning [preformed enterotoxin]
What are the 4 stages of bacterial adherence and what drives each step?
- attachment: mediated by non-specific forces
- adhesion: driven by specific adhesion-receptor interactions
- aggregation: bacterial macrocolony formed imprved nutritional microenvironment and protects bacteria from host defenses
- dispersion
What are 4 potential sources for bacterial contamination of intravascular catheters?
- contamination of catheter hub
- contamination of infusate
- transcutaneous migration
- hematogenous seeding from different site
What is “slime layer”
staph aureus and epidermis both form slime layer around foregin body
What are the host immune responses to staph aureus infection?
- primarily mechanical by epidermis [if dont have portal of entry can’t get through epidermis]
- opsonization
- neutrophill phagocytosis
What are the clinical manifestations [disease] associated with staph aureus?
- skin and soft tissue infection [most common]
- vascular infection [endocarditis]
- metastatic infection [septic arthritis]
- osteomyelitis
- hospital acquired infection
- toxic shock
- food poisoning [toxin mediated]
What are the two non-suppurative complications of staph aureus
- toxic shock [tsst-1/enterotoxin mediated]
- food poisoning [toxin mediated]
What is the difference staph and strep vascular infection?
- staph can land anywhere, does not require damaged surface or molecular mimicry
- strep requires previous damage to cause endocarditis or works by molecular mimicry in rheumatic fever
S aureus buttock abscess - treat?
- growing vertically into bigger puss
- need to treat by drainage and antibiotics
why are diabetics prone to infection [and s aureus in particular]?
high blood sugars paralyze hemotaxis–> blunt immune response
What two things can commonly cause impetigo?
strep pyogenes
staph aureus
How do you determine staphylococcoal from streptococcal cellulitis?
- strep pyogenes and staph aureus both pus-formers
- BUT –> staph produces microabscesses with visible exudation of pus. staph cellulitis can also be subtle and barely noticeable
What is chalazion?
- infected meibomian gland in eye
- due to colonizationo f conjunctiva by staph
Why might staph endocarditis require emergency valve replacement?
bacterial vegetations on the valve might embolize to other parts of the body
true or false: s. aureus can only infect previously damaged valve
false – staph aureus can infect any valve normal or damaged
by contrast, strep can only infect previously damaged valves
What are roth spots?
- retinal hemorrhages caused by septic microemboli from bacterial endoccarditis
What is MRSA?
- methicillin-resistant staphylococcus aureus
- very limited therapeutic options
- formerly almost exclusively hospital-acquired, no more common in community
What is staphyloccocal food poinsoning?
- common cause of acute food poisoning
- asocated with unrefrigerated dairy
- ingestion of preformed toxin causes vomitting and diarrhea
- no invasion by organism or superantigen involved
Treatment of staph infections?
- cell wall active semisynthetic penicillins [oxacillin, nafcillin]
- certain cephalosporins [cefazolin]
What is treatment of MRSA and other resistant strains?
vancomycin
Is staphylococcus epidermidis coagulase positive or negative?
negative
What are general features of staph epidermidis?
- coagulase negative
- normal inhabitant of skin
- rarely causes disease in normal host in absence of foreign bodies
- associated with infections related to medical devices
- relatively resistant to common antibiotics
What is mech of s epidermidis as a pathogen of medical devices?
- forms biofilm [slime layer] = colonizes polymer surface of intravascular catheter with thick slime multilayer containing exopolysaccharide and organisms embedded within it to keep making more exopolysaccharide
- microcolonies resistant to antibiotics
Two types of clinical syndromes assocated with Staph epidermidis?
- infection associated with intravascular device
2. central nervous system infection associated with foreign bodies
What is main clinical syndrome of saphylococcus saprophyticus?
- causes UTIs
- has receptor that allows it to bind mucosal receptors in GU tract and cause ascending infection
Is staphylococcus saprophyticus resistant or sensitive to antibiotics?
- highly sensitive to all antibiotics
