Flashcards in Staph and Strep Deck (36)
Common characteristics of Staph and Strep
gram positive cocci
pyogenic- cause suppurative infections
-commensal of mucous membranes and skin
Staph- differentiating characteristics
Opaque, creamy colonies
Cells resemble bunches of grapes
Produce catalase- breaks down H2O2
Resistant to bile salts (grow on MacConkey agar)
Grow on simple media (nutrient agar)
Generally survive well in environment (hospitals)
Pus produced is thick and creamy
Strep- differentiating characteristics
Translucent, greyish colonies
DON'T produce catalase
Sensitive to bile salts (don't grow on MacConkey)
don't grow on simple media (nutrient agar)
generally survive poorly in the environment
Pus produced is serosanguinous
Strategies of extracellular pathogens
S. aureus- main cause of mastitis in cattle, but affects many species
S. pseudintermedius- pyoderma in dogs- skin inflammation
S. hyicus- exudative dermatitis in pigs (also in horses and cattle)- skin infection which allows leakage of serum
S. epidermidis- skin commensal in all species. association of dz less common, although it forms biofilms on plastics--> can cause bloodstream infection.
Staph aureus- cultural characteristics
2 different hemolysins: complete beta hemolysis due to alpha toxin- causes pore formation in cells (outpouring of cell contents); beta toxin- sphingomyelinase (sphingomyelin found in animal cell membranes)--incomplete (weak) B hemolysis.
MacConkey agar- lactose fermenters
Clump together d/t incomplete division along the planes
Differentiating Pathogenic from non-pathogenic Staph
S. aureus and S.pseuditermedius: coagulase, DNAse, hemolysis and catalase positive
S. hyicus: coagulase variable, DNAse and catalase positive, hemolysis negative
Non-pathogenic strains (s. epidermidis): coagulase, DNAse, hemolysis negative, catalase positive.
Coagulase test- used in human testing
Coagulase converts fibrinogen (soluble) to fibrin (insoluble). will get a clump in the plasma if +ve
DNAse test-used in animal testing
DNAse: clearing when organism is producing DNAse. enzyme breaks down DNA in the medium.
Neutrophil extracellular traps (NETS)
Pathogenic staphs make DNAse to escape NETS. NB: so do streps
Neutrophils explode along prolonged contact with extracellular bacteria. Any bacteria in vicinity is engulfed by cytoplasmic contents. If bacteria produce DNAse, can escape nets.
Pathogen associated molecular patterns (PAMP)
recognize bacteria and counteract them. PAMPs secrete cytokines and interleukins to try to recuir neutrophils. Activate complement on the surface of bacteria--> phagocytose. AMP to kill bacteria. Transferrin and lactoferrin to control bacterial growth
Staph virulence factors
Adherence: fibronectin binding protein and other ECM binding proteins
Toxins: exfoliative toxins (skin disease), super antigens (TSS and enterotoxins)
Degradative enzymes: DNAse, lipases, proteases, hyaluronidase
Iron-uptake systems: overcome regulation of low presence of iron. can remove iron bound from transferrin or lactoferrin
Antichemotaxis: chemotaxis inhibitory protein of staph (CHIPs); extracellular adhesion protein (EAP)
ANti-opsonic and anti-phagocytic: staph complement inhibitor (SCIN); protein A; capsule; staphylokinase; fibrinogen binding proteins; hemolysins and leukocidins
Staph resistance to opsonisation and phagocytosis
1. binding of the Fc portion of antibody to protein A instead of the antibody binding portion--WBCs can't latch on--interfere with phagocytosis
2. staph complement inhibitor (SCIN) inhibits complement activation pathways
3. capsule production: resists phagocytosis
4. fibrinogen binding protein-surface bound fibrinogen--inhibits opsonisation
5. hemolycins and leukocidin: inhibit or lyse phagocytes.
S. aureus disease in animals
mastitis, bumble foot in poultry (foot abscess)
Staph skin diseases
Pyogenic infections following penetration of skin, boils etc
Humans-->s. aureus- scalded skin syndrome
Pigs--> s. hyicus- greasy pig disease
Dogs--> s. pseudintermedius- pyoderma
Exfoliative skin diseases
virulence factor: exfoliative toxin (ET)
staph aureus has at least 4 ET, including protease which cleaves desmogelin in desmosomes (important in cell adhesion- resist shearing forces)--> separation of upper epidermis
S.hyicus - at least 5 ETs
S. pseudintermedius- an ET-like toxin has been described
NB: ETs are specific for species
Tampon Disease- TSS
high fever, hypotension, renal failure. Particular S. aureus strain producing TSS toxin -1 -- superantigen.
tampons absorb Mg2+--> perhaps low [MG2+] acts as a cue for S. aureus to produce TSST-1?
Bacteria/toxin are localized but produce systemic effects.
normal antigen: stimulate massive release of pro-inflammatory CKs--> shock
S. aureus and Strep pyogenes produce many SA. Mitogenic for T-cells, cause cytokine storm.
Community acquired S. aureus
necrotizing pneumonia seems to be hallmark of community acquired S. aureus. Panton-valentine leukocidin kills WBCs of host.
Alpha hemolysis: incomplete breakdown of hemoglobin-- greenish tint
Beta hemolysis: complete destruction of RBCs
Pyogenic strep are beta hemolytic but not ALL pathogenic strep are beta-hemolytic.
Streptococci cultural characteristics
S. equi equi: beta hemolytic
S. equi zooepidemicus: beta hemolytic
S. uberis (cause of mastitis): maybe alpha or non-hemolytic on Edward's medium , grow on sheep blood agar. Splits aesculin--> colonies appear black.
No growth of strep on MacConkey agar (sensitive to bile salts).
S. agalactiae: beta hemolysis, doesn't split aesculin
S. dysgalactiae: alpha hemolysis, doesn't split aesculin
originally discovered when it was found that CHO capsules of strep were antigenically different and that isolates fell into a limited number of antigenic groups.
Virulence factors of pyogenic (Beta-hemolytic) streptococci
Adherence to epithelium: fibronectin binding proteins; lipotechoic acid- bind to upper resp. epithelium
Systemic toxicity: streptococcal superantigens
Degradative enzymes: DNAases, proteases, hyaluronidase, streptokinase, cysteine protease
anti-chemotaxis: C5a peptidase; IL-8 protease (attracts neutrophils)
Anti-opsonic and anti-phagocytic factors: capsule, M protein and M-like proteins, hemolysins (streptolysins O and S)
M-protein: structure and function
Cell membrane, cell wall, factor H-binding region, host cross-reactive epitopes, fibrinogen binding region--different binding sites to different host molecules. Hypervariable region is hydrophobic and resists action of phagocytosis. Hypervariable regions has little variation in S. equi and lots of variation in S. pyogenes.
Basically M-protein allows bacteria to cover itself in host molecule.
If you add M-protein specific antibodies, or mutate it so that it's not on the surface, bacteria is phagocytosed.
S. agalctiae-2 %; S. dysgalactiae- 7%, S. uberis- 28%, Staph aureus- 25%, E.coli 25%
S. uberis and S. dysgalactiae: environmental mastitis
S. agalactiae: contagious mastitis
Peracute mastitis, acute, chronic and subclinical mastitis from all of these bacteria.
Equine group C streptococci
S. equi equi and S. equi zooepidemicus
S. zooepidemicus general characteristics
Opportunistic e.g. secondary resp infections, wound, metritis etc
Infects various host species: cattle, sheep, dogs etc
Can cause zoonotic infection
S. equi equi general characteristics
VERY host specific- only horses
Fever, Swollen LNs (constrict airway), discharge--> strangles
Septicemia (fatal)= bastard strangles
quarantine and ABX treatment