Staphylo'cocc'us and Strepto'cocc'us Flashcards
Staph and Strep share some common characteristics: Gram + or -? Aerobic or anaerobic? Spore-forming? Motile? What kind of infections do they cause? Where are they commensals on the body?
Gram positive Facultative Anaerobes Non spore-forming Non motile Cause supparative, pyogenic infections Commensals of mucous membranes and skin
How would you describe the texture of their magical pus?
Staph- thick and CREAMY
Strep- thin and serous
Describe staph/strep colonies
Staph- Opaque, creamy colonies
Strep- Translucent, greyish colonies
Which of staph/strep will produce catalase?
STAPH WOOO!
Which of staph/strep will grow on both MacConkey and Nutrient agar?
Staph, he survives well in the environment and is resistant to bile salts- STAPHIA MAFIA
Strep is sensitive to bile salts and won’t grow on Nutrient agar- Strep is a pussy.
Which of staph/strep form grape-like colonies, clusters due to incomplete divisions?
Staph- he is cool and mafia so he keeps his friends close
Strep form long chains. Awkward strep chains. His main strategy for life is to avoid phagocytosis because he does not like personal contact.
Give 3 strategies of extracellular pathogens
Counteract complement
Counteract phagocytes
Acquire nutrients
Name 4 staphylococci of veterinary importance
S. aureus
S. pseudintermedius
S. hyicus
S. epidermidis
Which of the 4 staphylococci of veterinary importance is this?
Golden colonies
Lactose Fermenter
Alpha and Beta toxins- haemolysis
S. aureus
Which 4 tests would you carry out to differentiate pathogenic from non pathogenic Staphylococci ?
Which two species are positive for all 4 tests?
Coagulase
Catalase
DNAase
Haemolysis
S.aureus and S. pseudintermedius are positive for everything (sluts)
Non- pathogenic strains are only positive for catalase
Does Alpha toxin cause complete or incomplete haemolysis?
Complete
Beta causes incomplete
To differentiate between pathogenic strains of Staph, use biochemistry, API Staph. What does API stand for?
Analytical Profile Index
Describe the Coagulase Test
Fibrinogen (soluble) + coagulase –> fibrin clot (insoluble)
Clot formation= POSITIVE
Describe the DNAase Test
DNA is impregnated into the medium, it shows as a white precipitate. If DNAase is present in the sample, the medium will turn clear around the colonies
Neutrophil extracellular traps (NETs)
Neutrophils explode upon prolonged contact with bacteria, in order to externalise their contents and engulf the surrounding bacteria. Pathogenic staphs (and streps) make DNAase to stop this from harming them- they can escape NETs
Staph Virulence Factors (6)
Adherence Anti-chemotaxis Anti-opsonic & anti-phagocytic Iron-uptake systems Degradative enzymes Toxins
Staphylococcal resistance to phagocytosis, what mechanism is used?
- Binding of the Fc portion of antibody to Protein A
- Staphylococcal complement inhibitor (SCIN) inhibits all complement (C’) ativation pathways
- Capsule production- the capsule activates and binds complement, but it is not opsonised or phagocytosed
- Fibrinogen binding protein- surface bound fibrinogen. Inhibits opsonisation
- Haemolysins and leukocidin- Inhibit or lyse phagocytes
ET COME HOOOOME! What does ET stand for?
Exfoliative toxin S.aureus – at least 4 ET Protease – cleaves desmoglein 1 in desmosomes Separation of the upper epidermis S.hyicus At least 5 ET S.pseudintermedius A ET-like toxin has been described
Antigens stimulate < 0.01% of T cells
How much do SuperAntigens stimulate?
Stimulate 2-20 % of T cells, leads to
Massive release of pro-inflammatory cytokines then shock
S.aureus and Streptococcus pyogenes produce many SA
Streptococci- two types of haemolysis Alpha and Beta- appearance?
Alpha- If zone is darker than the media/ green. This leaves the RBCs intact but causes the Hb to change colour. More pronounced on heated blood agar plates.
Beta- clear, yellow zone around the colonies of the bacterium, due to the action of haemolysins that lyse the RBCs, liberating the Hb which can then diffuse away from the area.
Complete- clear
Incomplete- opaque and fuzzy
How do you type Strep?
Lancefield typing – place streptococci in (Lancefield) groups –A, B, C etc
Based on differences in carbohydrate antigen in cell wall.
Use antisera against different antigens to type
Pathogenicity Factors of Pyogenic B-haemolytic streptococci
Adherence to epithelium Anti-chemotaxis Systemic Toxicity- super antigens Anti-opsonic and anti-phagocytic factors Degradative Enzymes
What are the 3 most common causes of Bovine Mastitis?
S. uberis 28%
Staphylococcus aureus 25%
E. coli 25%
S. uberis, S. agalactiae, S. dysgalactiae- Three streps that cause mastitis. Which are environmental and which is contagious?
S. agalactiae is contagious, the others are environmental.
