Bacteria - Gram positive: Staph and Strep

Cards (73)

  • What is cocci
    Round bacteria
  • What is Bacilli
    Rods
  • When gram stained what colour does gram positive bacteria go
    purple
  • When gram strained what colour does gram negative bacteria go
    Pink
  • What are the 4 stages of gram staining
    1 - application of crystal violet
    2 - Application of iodine
    3 - application of alcohol wash - to decolourise
    4 - application of Safranin - which is a counterstain
  • What are the major differences between gram positive and gram negative bacteria
    Gram positive has a thick proteoglycan layer
    Gram negative has an outer membrane - which makes it more resistant to antibodies
  • What category of bacteria does Stpahylococcus and streptococcus fall into
    Gram positive cocci
  • What are the traditional methods of identification between staph and strep
    Ability to digest different sugars, enzymes and blood etc
  • What is the most modern method for bacteria identification
    MALDI-TOF
    'bacterial fingerprint'
    Specific to each species - can differentiate from ones that look physically similar
    The laser breaks down bacteria into protein fragments separated by their mass: charge ration
  • What are the pros and cons of using Maldi-toff for identification of bacteria
    Pros -
    rapid, high throughput, broad application, low running costs, direct from culture plates
    cons -
    Machine is VERY expensive, ongoing servicing costs
  • What are the 3 bacterial species that are gram positive cocci
    Staph
    Strep
    Enterococci
  • What are the 9 species of gram positive bacilli and which two are spore formers
    Spore formers - clostridium and bacillus
    Listeria
    Erysipelothrix
    Corynebacterium
    Rhodococcus
    Trueperella
    Actinimyces / norcardia
    Mycobacterium!
    + anaerobes
  • What test is used to differentiate between Staphylococcus and streptococcus, enterococci
    Catalase test
  • What does a catalase positive tests result mean
    Staphylococcus
  • What does a catalase negative test result mean
    Streptococci or enterococci
  • What is the catalase test and how does it work
    3% hydrogen peroxide - to see if the bacteria can break it down into hydrogen and oxygen - phagocyte produce H2O2
    Seeing bubbles in the the tube = positive so likely staph
  • What type of species of bacteria is it likely to be if you see clumps
    Staphylococcus
  • What type of plate do you get staph growth on
    Mannitol slat agar
  • What happens with staph on a blood agar plate
    Haemolysis - this varies by species and the type of blood in the agar - may indicate pathogenic potential
  • What test differentiates between different species of staphylococcus
    Coagulase test
  • What types of haemolysis are there
    Beta - complete
    Alpha - incomplete
    gamma - basically none
  • Is coagulase positive or coagulase negative more pathogenic
    Coagulase positive
  • Which 3 species of staph are coagulase positive
    Staph Aureus
    Staph Pseudintermedius - dogs
    Staph Hyicus - pigs
  • What 3 species are coagulase negative
    staph epidermis
    staph xylosus
    Staph capitis
  • How does the slide coagulase test work
    Fibrinogen binding protein is bound on the bacterial surface
    When plasma is added, clumping is visible
  • How does the tube coagulase test work
    The coagulase enzyme converts pro-thrombin to thrombin which converts fibrinogen to fibrin which is insoluble and so clotting occurs
    THIS TAKES 24 HOURS!!
  • Is staphylococcus a normal commensal and if so is it opportunistic
    Yes and yes
    However it is very resistant to drying out
  • Staphylococcus adheres to squames but different species have host preferences: Which host does aureus, pseudintermedius and hyicus like
    Aureus - humans
    Pseudintermedius - dogs
    Hyicus - pigs
    Good at staying on the skin but can bind to others
  • How does adhering to squames lead to a transmission issue
    Because they are shed and can survive in the environment
  • Give examples of diseases that S. aureus and S. pseudintermedius cause
    Wound infections
    abcesses
    Canine pyoderma
    Otitis externa
    Cellulitis
    Tick pyaemia
    Ascending bovine Mastitis
    Urinary tract infections
    Osteomyelitis - joint infections that can be found after surgery
  • What are the 3 different pathogencity factors of S. aureus and S. pseudintermedius
    Secreted exotoxins
    Evasion of the immune system
    Cell surface - bound
  • What are the different secreted exotoxins from staphylococcus

    Haemolysins - a/b
    Leucocidins - b / pvl
    TSST-1 - aureus only
    Hyaluronidase - aureus
  • How does staphylococcus evade the immune system
    Facultative intracellular pathogen
  • What is cell surface bound by staphylococcus
    Fibrinogen binding
    Protein A
    Capsule - aureus
  • Which species of staphylococcus produce alpha toxin
    Aureus and pseudintermedius
  • What does alpha toxin do
    Haemolytic
    Results in B-haemolysis on blood agar
    Necrotising
    Cell damage - mostly mast cells and platelets
  • What does beta toxin do
    Sphingomyelinase enzyme
    Destabilising - not full rupture - becomes deeper over time
    Membrane damage and fragile red blood cells
    Necrosis
    Lyses proliferating lymphocytes - effects long term immune response
  • Which species of staph is Leukocidins described in
    Aureus
  • How do leukocidins work
    They create pores in the membrane
    Lead to leukocyte destruction especially neutrophils
    Necrotising pneumonia
    NOT OF VETERINARY IMPORTANCE
  • What species of staph is TSST-1 described in
    Aureus