Streptococcus Flashcards
Is streptococcus gram positive or gram negative?
Gram positive
Which type of haemolysis does streptococci group have?
Most oral streptococci and Strep pneumonia are alpha hemolytic- this means they cause partial hemolysis of blood agar plates.
Strep Anginosus and strep pyogenes is beta haemolytic so they cause complete hemolysis of blood agar plates.
Enteroccocus faecelis- is gamma hemolytic- doesn’t cause any hemolysis of blood agar plates
Group A streptococcus
These are groups like the strep anginosus which are beta haemolytic- the associated diseases from this pathogen ranges from scarlet fever to necrotising fascitis.
How can you differentiate between strep pyogenes or strep pneumonia?
This is done by viewing the sensitivity reaction to an antibiotic called bacitracin. Strep pyogenes has a sensitivity reaction towards this antibiotic.
What is the pathology of strep pyogenes?
From sore throat- scarlet fever- It causes skin infections, upper respiratory tract infections, rheumatic fever or gloommerulanepitis.
What are the virulence factors that strep pyogenes has?
1) superantigens- just like the staphylococcus one, it causes overstimulation of T cells that leads to the massive production of cytokines causing toxic shock that is induced by streptococci.
2) haemolysis- destruction of tissue
3) M protein- attachment- binds to fibronectin (factors that support the cells of the body)
4) destroy DNA, destroy peptidase and destroy hyaluronic acid.
What skin diseases do group A streptococci produce?
Impetigo- usually on the face- most common presentation in children and is highly contagious
cellulitis- deeper infection of the dermis that is not associated with nercosis
erysipelas- localised fever, nausea- this involves the lymphatic system- causes edema and associated chills.
Invasive GAS strains
Impetigo, cellulitis
Necrotising fascilits
These can penetrate mucus membranes and develop in lesion.
Acute streptococcal gingivitis
Acute streptoccocal gingivitis
This cause swelling of the gingiva, red and oedematous (swelling with excessive amounts of fluid)
often follows sore throat
Sore throat (pharyngitis in a disease state)-
how would you distinguish a viral or bacterial
Most cases of strep throat are likely to be viral but 15% are bacterial.
Bacterial- you see a sudden onset from mild to bad- you have fever, disruption of tissue. Strep pyogenes- very sudden onset- it goes from mild to aggressive quickly- you tend to get fever, tiny spots on the palate, red swelling.
Viral- you don’t get fever- you get a runny nose, cough and you have other type of eye and GI disturbances.
This can even progress to tonsilitis- inflammation of the nasal mucous membrane.
Group A streptoccoci- Strep pyogenes- Specific disease- Scarlet fever
severe form of strep throat- associated with a rash-
oral presentation- causes a red colouration of the tongue- it destroys peripheral vascular tissue so red blood cells leak out
Has superantigenicity capacity- chills, fever and can be life threatening.
Rheumatic fever (autoimmune disease)
This causes more systemic effects- joint pain, nose bleeds, inflammation of the joints and heart, Infection of the myocardium
What are the treatments for GAS?
Penicillin or erythromycin
Amoxicillin- Acceptable to children
CoAmoxy Clav-
What innate factors does the respiratory tract have to limit colonisation?
Upper respiratory tract- mechanical washing, cough response, mucocillary response,
Non-ciliated cells have mucus
What are the key surface components that support colonisation of the pharynx?
M protein- binding to fibronectin. Involved in adhesion and evading the immune response
Hyaluronic acid- this is a capsule that surrounds the bacteria and looks like the host- it can hide from the immune response and attach to keratinocytes.
