Staphylococcus & Streptococcus Flashcards
What kind of bacteria are Staph and Strept?
- Gram positive cocci
- Facultative Anaerobes
- Non spore forming (v. Bacillus/ Clostridia)
- Non motile
- Commensal of mucuous membranes and skin
- Pyogenic- suppurative infections. (pus)
Differentiation characteristics of Staph?
- Opaque creamy colonies.
- Grape like clusters
- Produce catalase- this breaks down H202 (used to kill bacteria) into H20 and water.
- Resistant to bile salts therefore they grow on MacConkey Agar.
**–> MacConkey Agar contains bile salts and is used to grow Gram Negative bacteria to different between lactose/ non lactose fermenters. However since Staph is resistant to bile salts which are used to prohibit growth of said Gram positive bacteria, Staph will go ahead and grow on this medium. **
- Grow on simple media (nutrient agar)
- Survive well in the environment.
Differentiation Characteristics of Strept?
- Translucent, grey colonies
- **Do not produce catalase **
- Sensitive to bile salts therefore will NOT grow on Macconkey agar
- Won’t grow on simple nutritent agar either.
- Poor survival in the environment.
Staph and Strept are extracellular pathogens:
What are the strategies of extracellular pathogens for survival?
- Counteract complement
- counteract phagocytes
- Acquire nutritens.
Which species does S. aureus mainly effect and what disease does it cause?
Cattle- Mastitis.
Which species does S. pseudintermedius mainly effect and what disease does it cause?
Dogs- pyoderma (skin pustules and inflammation)
Which species does S. hyicus mainly effect and what disease does it cause?
PIgs- exudative epidermitis (Greasy Pig Disease)
Which species does S. epidermitis mainly effect and what disease does it cause?
All species- skin commensal (causes infection in hospitals found on plastics)
Culture Characteristics of S. aureus.
Beta Hemolysis
Alpha Hemolysis
Hemolysins involved in each.
- Staph cultures wil show creamy, opaque culturs.
- They are resistant to bile salts therefore they are lactose fermenters on MacConkey agar (will grow)
- Produces hemolysins:
1. Alpha
2. Beta - Alpha and Beta hemolysins are both shown in **Beta- Hemolysis. **
- Alpha hemolysin will show complete hemolysis surrounding the culture (Clear)
- Beta hemolysis will show incomplete hemolysis surround the culture. (Yellow and fuzzy)
- However, even though one is complete and other is incomplete, both are showing Beta hemolysis.
- Alpha hemolysis DOES NOT show clear (complete) or somewhat clear (incomplete) zones of hemolysis surrounding the culture. Rather it shows up darker (greenish color). The mechanism as to why this happens is unknown but possibly due to conversion of released Hemoglobin to Methemoglobin.
- Alpha hemolysis does not contain alpha hemolysin.
Which test is best used in Veterinary Medicine to different from pathogenic and non pathogenic Staphylococcus?
- DNAase test.
- Will show positive for S. aureus, S. pseudintermedius, S. hyicus.
- Will show negative for non pathogen strains (S. epidermidis)
- To differentiate between pathogenic v. non-pathogenic, DNAase found in pathogenic staph breaks down DNA in the medium, flood it with HCl which will precipiate unharmed DNA in the medium and leave clear areas around the colonies which are DNAase positive since they destroyed the DNA in the medium.
What test is best to use when differentiating between pathogenic Staphylococcus strains?
API. Analytical Profile Index.
A numerical profile is generated for each organism tested. The ogranism is identified by consulting a manual of numerical profiles or computer database.
The numbers can range from +3 to 0.
What are Neutrophil extracellular traps? NETS
- These are networks of extracellular fibers, composed of DNA from neutrophils used to bind pathogens.
- Pathogenic Staphs will produce DNAase to escape NETS. (Strept will also produce DNAase)
- The DNAase will externalize the internal compartments of the NET therefore allowing the bacteria to escape and survive.
What are Staphylococcus Virulence factors?
-
Adherance
a. Fibronectin binding protein -
Toxins
a. Superantigens-Enterotoxins
b. Exfoliatve Superantigen -
Degradative Enzymes
a. DNAase - Iron-uptake systems
-
Anti-opsonic & anti-phagocytic
a. Staphylococcal complement inhibitor
b. Protein A.
c. Capsule
d. Fibrinogen binding proteins.
e. Hemolysins -
Anti chemotactic
a. Chemotaxis inihibitory proteins.
Staphylococcal Resistance to opsonization and phagocytosis.
- Binding of the Fc portion of the antibody to protein A (outer surface of bacteria) rather than the appropriate antigen binding site of the antibody Fab. IgG is bound the wrong way and this interferes with phagocytosis.
- **Staphylococcal complement inhibitor (SCIN) inhibits complement activation. **
- **Capsule production: **
Activates and binds complement but doesn’t allow opsonization or phagocytozing. -
Fibrinogen binding protein
Fibrinogen is a host molecule, its binds to proteins on the bacteria and disguises it as own. -
Hemolysins and leukocidin:
Inhibit or lyse phagocytes
Staphylococcal associated skin diseases:
- S. aureus (humans) scalded skin syndrome
- S. hyicus (pigs): Greasy pig syndrome
- S. pseudintermedius (dogs): pyoderma
Pyogenic infections will ensue once bacteria has penetrated the skin.
- Exfoliative skin conditions
Exfoliative conditions skin Disease:
What strains are involved from what bacteria?
What are the virulence factors (toxins) involved?
what is the mechanism of destruction
Prevalent Staphylococcus strains on the skin of the host.
- S. aureus (humans)
- S. hyicus (pigs)
- S. pseudintermedius (dogs)
The toxin associated with exfoliative skin conditions is the Exfoliative Toxin (ET) which acts as a protease to separate the epidermis from the dermis.
Tampon Disease:
How does this occur?
What are the symptoms associated?
What bacteria/ strain is the cause?
What is the cue for this process to occur?
- Staphylococcal toxic shock sydrome (TSS)
- Increase in TSS in menstruating women. This was associated with superabsorbant tampons.
- Causes hypotension, renal failure, high fever.
- S. aureus producing toxic shock syndrome toxin-1 (TSST-1) is a SUPERANTIGEN.
- Low Mg++ acts as a cue for S. aureus to produce TSST-1.
Antigen v. Superantigen
Antigens stimulate <.01% of T cells and assoicated cytokines.
Superantigens stimulate 2-20% of T cells causing a massive release of pro inflammatory cytokines inducing SHOCK.
The CYTOKINE STORM is reponsible for the massive shock.
What kind of hemolysis does S. equi show?
Complete B- hemolysis
What kind of hemolysis does S. zooepidemicus show?
Beta hemolysis.
What kind of hemolysis does S.uberis show?
Alpha hemolysis.
What Steptococci strains are of importance in horses?
S. equi subsp. equi– causes strangles
S. equi subsp. zooepidemicus
In cattle, what are the important Strept strains and what disease do they cause? Which strains are enviromental and which strains are contagious?
- S. agalactiae **(contagious) **
- S. uberis (environmental)
- S. dysgalactiae (environemental)
All three cause mastitis in cattle.
What Strept species is of importance in dogs and what disease does it cause?
S. canis causing septicemia.
