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Staphylococcus and Streptococcus. Nightmare bacteria. Super bugs. Flesh eating bacteria. Streptococcal necrotizing fasciitis. MRSA. Common characteristics. Staphylococcus. Streptococcus. Gram positive cocci Facultative anaerobes Non-sporing, non-motile Important pathogens

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nightmare bacteria
Nightmare bacteria

Super bugs

Flesh eating bacteria

Streptococcal necrotizing



common characteristics
Common characteristics



  • Gram positive cocci
  • Facultative anaerobes
  • Non-sporing, non-motile
  • Important pathogens
  • Pyogenic –suppurative infections
  • Commensals of mucous membranes and skin
differentiating characteristics


  • Opaque, creamy colonies
  • Produce catalase
  • Resistant to bile salts (grow on MacConkey agar)
  • Grow on simple media (Nutrient agar)
  • Generally survive well in the environment


  • Translucent, greyish colonies
  • Don’t produce catalase
  • Sensitive to bile salts (don’t grow on MacConkey agar)
  • Don’t grow on simple media (Nutrient agar)
  • Generally survive poorly in the environment
Differentiating characteristics
laboratory diagnosis
Laboratory diagnosis
  • Specimens:
    • May include exudates, pus, mastatic milk, skin scraping, etc
  • Direct microscopy:
    • To examine gram stained smears (pus/exudates)
  • Isolation:
    • Routine medium is blood agar (24 hours).
    • MacConkey agar in parallel, to detect any gram negative bacteria.
differentiating pathogenic from non pathogenic staphylococci
Differentiating pathogenic from non pathogenic Staphylococci
  • Coagulase correlates with pathogenecity.
  • Micrococci are O-F positive, Streptococci & enterococci are … negative?
coagulase and dna tests
Coagulase and DNA tests

DNAse agar. Not definitive



“flesh eating”




Endocarditis &



Scalded Skin

S. aureus Infections

Toxic Shock




Impetigo: A contagious skin infection that is characterized by the eruption of superficial pustules and the formation of thick yellow crusts, commonly on the face.

Septicaemia: blood poisoning caused by pathogenic microorganisms and their toxic products in the bloodstream

Osteomyelitis: infection of bone and bone marrow in which the resulting inflammation can lead to a reduction of blood supply to the bone


Strategies of extracellular pathogens

Counteract complement

Counteract phagocytes

Acquire nutrients

staphylococcus virulence factors


  • Fibronectin-binding protein
  • Extracellular adhesion
  • protein (Eap)
  • Anti-chemotaxis
  • Chemotaxis inhibitory protein
  • of staphylococci (CHIPS)
  • Toxins
  • Exfoliative toxins
  • Superantigens
  • -Toxic shock toxins
  • - Enterotoxins
  • Degradative enzymes
  • DNAse
  • Lipases
  • Proteases
  • Hyaluronidase
Staphylococcus virulence factors
  • Anti-opsonic & anti-phagocytic
  • Staphylococcal complement
  • inhibitor (SCIN)
  • Protein A
  • Capsule
  • Staphylokinase
  • Fibrinogen-binding proteins
  • Haemolysins + Leukocidins

Iron-uptake systems

Staphyloferrin B

staphylococcal resistance to phagocytosis

1. Binding of the Fc portion of antibody to protein A

Interferes with phagocytosis

2. Staphylococcal complement inhibitor (SCIN) inhibits complement activation -

3. Capsule production

Inhibits all complement (C’)

activation pathways



Activates and binds complement, but not opsonised or phagocytosed

4. Fibrinogen binding protein -surface bound fibrinogen

Inhibits opsonisation

5. Haemolysins and leukocidin

Inhibit or lyse phagocytes

Staphylococcal resistance to phagocytosis
s aureus disease in animals
S.aureus disease in animals


Bumble foot

staphylococcal skin diseases
Staphylococcal skin diseases

Pyogenic infections following penetration of skin, boils etc –many species.

Exfoliative skin diseases.







Scalded skin syndrome

Greasy pig disease


exfoliative conditions skin diseases
Exfoliative conditions skin diseases
  • Prevalent Staph on skin of particular host
    • Humans = S.aureus
    • Pigs = S.hyicus
    • Dogs = S.intermedius
  • Virulence factors: Exfoliative toxin (ET).
  • S.aureus – at least 4 ET
    • Protease – cleaves desmoglein 1 in desmosomes
    • Separation of the upper epidermis
  • S.hyicus
    • At least 5 ET
  • S.intermedius
    • An ET-like toxin has been described
tampon disease
“Tampon disease”
  • Staphylococcal toxic shock syndrome (TSS): high fever, hypotension, renal failure
  • Increase in staphylococcal TSS in menstruating women in early 1980’s in USA
  • Particular S.aureus strains producing toxic shock syndrome toxin-1 (TSST-1) is a SUPERANTIGEN
  • Associated with super absorbent tampons
  • ? Absorb Mg++ low [Mg++] act as cue for S.aureus to produce TTST-1.
superantigens sa



Stimulate 2-20 % of T cells

Stimulate < 0.01% of T cells

Massive release of pro-inflammatory cytokines


Superantigens (SA)

Superantigens (SAgs) are a class of antigens which cause non-specific activation of T-cells resulting in polyclonal T cell activation and massive cytokine release. SAgs can be produced by pathogenic microbes as a defense mechanism against the immune system.

S.aureus and Streptococcus pyogenes produce many SA

pattern recognition receptors





Pattern-recognition receptors

Toll-like receptors (TLRs)



Toll-like receptors (TLRs) are a class of proteins that play a key role in the innate immune system. They recognize structurally conserved molecules derived from microbes. Once these microbes have breached physical barriers such as the skin or intestinal tract mucosa, they are recognized by TLRs which activates immune cell responses.

LPS, lipid A


Bacterial DNA

host defence against staphylococcus aureus infection require recognition of bacterial lipoproteins
Host defence against Staphylococcus aureus infection require recognition of bacterial lipoproteins

Juliane Bubeck Wardenburg, Wade A. Williams, and Dominique MissiakasHost defenses against Staphylococcus aureus infection require recognition of bacterial lipoproteinsPNAS 2006 103: 13831-13836

S.aureus mutant can not make lipoproteins

Infection of mice


S.aureus 90%

S.aureus mut 20%

streptococi cultural characteristics
Streptococi cultural characteristics





No growth

typing of streptococci
Typing of Streptococci

Superficially grouped based on their growth on blood agar plates into:

  • Alpha haemolytic: produce green discoloration around the colonies, but RBCs are intact.
  • Beta haemolytic: lyse RBCs and produce clear zone around the colonies.
  • Gamma haemolytic: non-haemolytic. Most are not pathogenic.
laboratory diagnosis1
Laboratory diagnosis
  • Specimens:
    • May include exudates, pus, mastatic milk, skin scraping, etc
  • Direct microscopy:
    • Smears (pus/exudates) are fixed and gram stained.
  • Isolation:
    • Routine medium is blood agar (18-24 hours).
    • MacConkey agar as a selective media (to distinguish from Staph).
  • Identification:
    • Colonial appearance, G-stained smears, Catalase, Lansfield grouping, etc.
camp test
CAMP test
  • Based on the haemolytic synergism between S. aureus toxins and group B Streptococci.
  • A culture of Staph aureus is streaked across the centre of a blood agar plate.
  • A streak of the suspect of group B Streptococci is streaked at right angle (90 degree).
  • After 24 hour incubation, a positive CAMP test is indicated by an arrow-head of complete haemolysis.
typing of streptococci1
Typing of Streptococci

Lansfield serologic typing – place streptococci in 22 (Lansfield) groups (A-V), based on differences in carbohydrate antigen in cell wall. Use antisera against different antigens to type.

pathogenicity factors of pyogenic haemolytic streptococci
Pathogenicity factors of pyogenic (-haemolytic) streptococci)
  • Adherence to epithelium etc:
  • Fibronectin binding proteins
  • Facilitate internalisation and subsequent localisation in the sub-epithelial space
  • Anti-chemotaxis:
  • C5a peptidase
  • IL-8 protease (ScpC)

Systemic toxicity

Streptococcal superantigens

  • Anti-opsonic &
  • anti-phagocytic factors:
  • Capsule
  • M-protein + M-like proteins
  • Haemolysins
  • (Streptolysins O & S)
  • Degradative enzymes:
  • DNAases
  • Proteases
  • Hyaluronidase
  • Streptokinase
  • Cysteine protease
m protein structure function1
M-protein - structure & function





Fibrinogen binding



Host cross-reactive epitopes

Factor H binding

(destroy C3 convertase and preventing opsonization)

bovine mastitis
Bovine mastitis

incidence (2004)

S. agalactiae 2%

S. dysgalactiae 7%

S. uberis 28%

Staphylococcus aureus 25%

E. coli 25%

equine group c streptococci
Equine Group C streptococci

S. equisimilis

Nasopharyngeal commensal

Opportunistic sepsis

e.g. wound

S. zooepidemicus

Nasopharyngeal commensal

Opportunistic e.g. 2° respiratory infections; wound; metritis; etc.

Infects various host species: cattle, sheep, dogs, etc.

S. equi

[carrier animals?]



Fever, swollen lymph nodes, discharge - STRANGLES

Septicaemia (fatal) - BASTARD STRANGLES

Highly contagious:

Quarantine & antibiotic treatment


Two fibronectin binding proteins- Adhesion

Two M-like proteins-SeM, SzPSe

Anti-phagocytic, anti-opsonic.

SzPSe present in S.zooepidemicus

SeM more important

Hyaluronic acid capsule




Streptolysin S (SLS)-like toxin, anti-phagocytic

Virulence factors of S.equi

strangles vaccine
Strangles vaccine

Intervet Equilis StrepE.

Live genetically modified S.equi vaccine, S.equi aro mutant

Administer inside upper lip.

s canis toxic shock syndrome
S.canis: toxic-shock syndrome

Canine toxic-shock syndrome. An emerging disease?

Symptoms of toxic shock syndrome vary depending on the underlying cause. Typically characterized by high fever, accompanied by low blood pressure, malaise and confusion, which can rapidly progress to coma, and multi-organ failure.

enterococci in veterinary medicine
Enterococci In Veterinary Medicine
  • Commensals in gut of humans and animals
  • Referred as group D Streptococci
  • Resistant to Bile Salts
  • Grow on MacConkey agar
  • Grow on 6.5% NaCl
  • Opportunist pathogens in all species
  • Bacteraemias in immunosuppressed animals and people
  • Often very resistant to antibiotics