Bacteria - Gram positive: Staph and Strep

• 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