2.2 Strep and Staph Flashcards
Streptococcus and Staphylococcus are both gram (+) or (-)
Gram (+)
How do we differentiate Streptococcus and Staphylococcus?
Catalase test
Streptococcus = Catalase (-) Staphylococcus = Catalase (+)
Describe the catalase test
Include the principals behind it and what the results would show
Catalase is an enzyme produced by organisms that live in oxygenated environments to neutralize the toxic oxygen metabolites H2O2 for protection.
Bacteria that are catalase (+) include strict aerobes and facultative anaerobes
Catalase (-) organisms lack the catalase enzyme and include anaerobes and facultative anaerobes
In the test Catalase (+) organisms will show gas bubbles representing the presence of catalase undergoing the following:
2H2O2 → 2H2O+ O2
Compare how Staphylococcus grow vs Streptococcus
Staph = clusters Strep = pairs or chains
What is the most pathogenic species of bacteria
Coagulase (+) Staphylococcus. Aures; capsular polysaccharide, protein A and leukocidin
List 4 virulence factors of Staphylococcus
1) capsule/slime layer: enables biofilm formation
2) adhesions: aid binding
3) Leukocidins: toxic product that allows invasion of WBCs (neutrophils)
4) Secreted factors
How do we differentiate different species of Staphylococci?
Explain this test
Coagulase test:
1) extract bacteria from site of infection
2) plate on solid substance (agar) to allow growth
3) once colony formation is present, extract and add plasma
4) if Coagulase (+) then Fibrinogen → fibrin clot, if Coagulase (-) then there will be no clot formation
What other enzyme is produced alongside coagulase (+) staphylococci?
How to these work together to aid virulence
Coagulase and Kinase are produced and allow bacteria to hide within the body
1) bacteria produce coagulase from within the cell
2) this causes recruitment of clotting factors
3) clot forms around bacteria protecting it
4) eventually when there is a lack of nutrition, bacteria dissolve the clot using kinases
5) bacteria can then enter blood stream and circulate body
Is Staphylococcus harmful under normal circumstances?
If it becomes harmful list 3 conditions a Staph Infection can cause
Bacteria is found as part of normal microbiota in nasal cavity and skin but can become opportunistic and lead to:
Pneumonia, skin infections and endocarditis (due to biofilm formation on stents)
Staph infection can cause osteomyelitis, what is this?
abscess formation on bone that can process to the bone shaft
What is the most common site of Staphylococcus infections
List 3 routes of infection
Skin through:
1) Skin (pores, hair follicles)
2) Wounds (scratches, cuts, burns)
3) Insect and animal bites
Name 4 ways the skin protects the body from pathogens entering
1) Keratinised
2) sebaceous glands produce antibacterial peptides
3) langerhan cells detect pathogens
4) Structure: multilayered, hardened and flattened
Name 3 toxin mediated staphylococcal diseases
1) TSS
2) Staphylococcal scalded skin syndrome
3) Staphyloccocal food poisoning
Name 3 similarities and 2 differences between Strep and Staph
Similarities:
1) gram-positive,
2) non-spore forming
3) non-motile
4) cocci
Differences:
1) Staph is catalase-positive (strep isn't)
2) Staph grows in clusters while strep grows in chains and pairs
What determines the type of skin infection that can occur (staph)?
List 4 skin infections caused by staph
The depth of the infection in the skin layer
1) Folliculitis
2) Boil
3) Cellulitis
4) Cutaneous abscess
What is folliculitis and what layer of the skin does it involve?
Common Staph infection: occurs in superficial hair follicles
causes recruitment of WBCs leading to red nodule formation
What is a Boil and what layer of the skin does it involve?
What are multiple boils known as?
Infection to the epidermis of the skin
Multiple = carbuncle
What is a cutaneous abscess?
What is found in the abscess?
a localized collection of pus in the skin and may occur on any skin surface.
Pus = dead leukocytes
What is Cellulitis?
What commonly causes it?
Who is most at risk?
Where on the body does it most commonly occur in adults and children?
Bacterial infection of the skin and subcutaneous tissue
Commonly caused by strep or staph.
Most at-risk people include those with a weak immune system and those who handle fish/meat/poultry or soil without gloves.
In adults: legs, face and arms
Children: face, anus
List 4 virulence factors of group A Streptococci
1) hyaluronic acid capsule inhibits phagocytosis
2) M protein and lipoteichoic acid for attachment
3) Extracellular products eg. pyrogenic toxin (causing the rash in scarlet fever), streptokinase, streptodornase, streptolysin
What are the 3 (major) classes of strep and what differentiates them?
What is their subsequent classification
Differentiated based on their appearance in sheep agar plate:
1) alpha; surrounded by green -> incomplete hemolysis
2) beta; surrounded by clear -> complete hemolysis
3) gama; red -> non-hemolytic
Subsequent classification is the Lansfield characteristic: study of glycoproteins on the surface
Name 3 most common acute diseases caused by Strep
1) Pharyngitis
2) Scarlet fever
3) Skin infections
What is Necrotizing fasciitis? What bacteria causes this?
How is the prognosis and what does treatment involve?
Trauma inoculates bacteria in fascia of muscles, highly toxic infection. Leads to Rapid necrosis along fascial planes
Most commonly cause Streptococcus pyogenes releasing exotoxin B (can be caused by MRSA)
Since the bacteria rapidly spreads up the fascial planes (not muscles) prognosis is poor without early and aggressive treatment.
Treatment includes antibiotics, surgery and amputation
Name 4 main upper resp tract defence mechanisms
1) mucociliary escalator
2) mechanical barriers: glottis and nasal turbinates
3) Reflexes: cough, sneeze
4) Maintenance of oropharyngeal flora (Saliva, local immunoglobulins, etc)
