Exam2Lec2StaphandStrep Flashcards
What are the microbiological properties of Staphylocci
gram positive cocci
single, pairs, short chains
most common: clusters
Facultative anaerobes
What are the three major species of Staphylocci?
Staphylococcus aureus
Staphylococcus epidermis
Staphylococcus saphrophyticus
What does protein A do?
binds FC region of IgG molecule
What do Teichoic acids do?
binds fibronectin on mucosal surfaces
What does leukocidin cause?
Call lysis then tissue destruction and abscess formation
What are the 5 virulence factors of S. aureus?
- Leukocidin
- Protein A
- Teichoic Acids
- Coagulase
- Hemolysins
What are the virulence factors of s. aureus that causes toxin-mediated disease? (and be specific as to what they cause)
Enterotoxins cause food poisoning
Exfoliative toxin causes SSSS
Toxic Shock Syndrome Toxin 1 causes Toxic Shock Syndrome
Panton Valentine Leukocidin (PVL) causes Necrotic Lesions involving skin and mucosa
What exactly are enterotoxins?
acid and heat resistant toxins that causes food poisoning
occurs 1-8 hours after toxin ingestion
short < 24 hours
What exactly are exfoliative toxin (exfoliatin) unique to s aureus?
toxin which causes staphylococcal scalded skin syndrome
erythema followed by desquamation
sloughing of outermost layer of skin
primarily occurs in infants
What exactly is toxic shock syndrome toxin (TSST1)
Toxin which causes hypotension, rash, desquamation, production of cytokines. Primarily occurs in women. Originally associated with tampon use.
What exactly is Penton-Valetine Leukocidin(PVL)?
PVL positive strains of S. aures are being found in increasing prevalence in community acquired MRSA.
Begins as skin infection and progresses toward a systemic infection w/ high mortality
severe soft bone and tissue infection, high chance of sepsis
Typically spread skin-to-skin contact and fomites
What are the two mechanisms of PVL?
- Opens up pores in cell membranes and leads to cell lysis
- entering cell and inducing apoptosis via capase cascade which leads to apoptosis
How can we distinguish between Staph and Strep?
Catalase test
Staph: catalase positive
Strep: catalase negative
How can we distinguish between the three major species of staph?
- Coagulase test
S. aureus= coagulase positive
S. epidermidis and S. saprophyticus= coagulase negative - Blood Agar Plate (BAP)
S. aureus= beta-hemolytic
S. epidermidis= non-hemolytic (gamma) - Mannitol Agar Culture
yellow: S. aureus
What does alpha, beta, and gamma hemolysis show? And what colors would they be?
Alpha: partial hemolysis (green/brown)
Beta: total hemolysis (clear)
Gamma: no hemolysis (no change)
How does mannitol salt agar work?
salt in agar kills off other types of bacteria except for staph
In mannitol salt agar, which type of staph will change color from pink to yellow via pH change?
s. aureus
What is the treatment for staph infections?
drainage of lesions
antibiotics (oxacillin, cephalosporin)
vancomycin for MRSA
note plasmid encoded beta lactamases common
What antibiotic is specifically used for MRSA?
Vancomycin
What are the microbiological properties of Streptococci?
gram positive cocci
pairs, short chains, long chains
NO CLUSTERS (this is staph)
Facultative Anaerobes
What are the three major species of Streptococci?
Streptococcus pyogenes
Streptococcus pneumoniae
Streptococcus agalactiae
Does Streptococcocus pnemoniae have a lancefield classification?
NO
What is the lancefield classifications? And which strep species is group a/b
It’s a classification system based on the carbohydrate composition of bacterial antigens found on their cell walls.
Group A= streptococcus pyogenes
Group B= streptococcus agalactiae
What are the Strep. pyogenes virulence factors?
- Streptolysins (hemolysins)
- Erthrogenic Toxin
- Exotoxin A
- Exotoxin B
- Capsule (some)
- M protein (all)
- Protein F
- Protein G (equivalent of protein A)
- C-Polysaccharide
What is the typical age range and asymptomatic carrier rate for respiratory infections for strep pyogenes?
5-15 years old, 5% (usually adults)
The epidemiology of group A infections of strep include skin infections which is contamination of abrasion. How is this spread and what is the age range of patients?
direct contact or shared fomites
patients 2-5 years old.
What is the pathogenesis of respiratory infections for strep pyogenes?
- Organisms inhaled (aerosols) and binds to epithelium via F protein
- Produces M protein: inhibits phagocytosis and complement
- Steptolyosin damages epithelial tissue
What are the suppurative (pus-producing) diseases of Strep pyogenes?
Pharyngitis, scarlet fever, streptococcal toxic shock, cellulitis, necrotizing fascitis
What are the non- suppurative (non-pus producing) diseases of Strep pyogenes?
rheumatic fever
glomerulonephrils