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Bacteria - Gram positive: Staph and Strep
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Created by
Kirsty Doughty
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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
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