Session 6 Lecture Notes Flashcards
What is a surface (for infection spread?)
An interface between a solid and either a liquid or gas
What are the 2 surface types on a patient?
- Skin
2. Mucosal surfaces
Give some examples of mucosal surfaces in our body
- Conjunctival (eye)
- GI
- Respiratory
- Genitourinary
What are the viruses that can be found on the skin?
Papilloma
Herpes simplex
What gram positive bacteria are found on the skin? List 3 of the most common types
- Staph aureus
- Coagulate negative staphylcocci
- Cornyebacterium
Name a gram negative bacteria found on the skin
Enterobacteriaceae
What gram positive bacteria is often found in contaminated blood samples?
Coagulase negative staphylococci
What causes tonsillitis?
Invasion of strep pyrogenes pharyngitis into the tonsils
What gram positive bacteria commonly causes infections around artificial joint surfaces?
Coagulase negative staphylococcus
What is a haematogenous spread of infection?
Blood borne spread of infection
What gram positive bacteria commonly cause endocarditis?
Coagulase negative staphylococcus
Give some examples of prosthetic surface infection locations
- Peritoneal dialysis catheter
- IV lines
- Prosthetic joints
- Cardiac valves
When might viridans streptococci cause endocarditis ?
- In a native heart valve
2. In a valve replacement that is less than a year old
When does coagulase negative staphylococci cause endocarditis?
In a heart valve replacement that is over a year old
What 2 bacteria commonly cause infections at prosthetic joint surfaces?
- Coagulase negative staphylococcus
2. Staph aureus
What structures of the bacteria help them to attach and create a biofilm?
Pilli
What are the 3 principles of biofilm formation?
- Autoinducers are secreted
- These bind to receptors on nearby bacteria
- This activates the receptor and causes more release of autoinducers and co-ordinates activity
Streptococci is a gram positive or negative bacteria?
Gram positive cocci
Streptococci can be classified by haemolysis
What are the 3 categories and how do they affect the RBCs on the blood afar plate?
- Gamma (non-haemolytic) - ie no destruction of RBCs
- Alpha haemolysis - partial break down of RBCs
- Beta haemolysis - complete break down of RBCs
What is the class of streptococci that produce alpha haemolysis?
Viridans streptococci
Why do viridans streptococci have a wet appearance on a blood agar plate?
They have a carbohydrate capsule which makes the organism more virulent
What could you expect to see on a blood agar plate of a streptococci that is beta haemolytic?
Clear zones where all that is left is the agar (jelly) - as the RBCs have been completed destroyed
What does the Lancefield classification of streptococci do?
Separate BETA-haemolytic streptococci (fully haemolytic) into groups based upon their cell wall antigens
What does the Sherman classification of streptococci do?
Separate Streptococci into 4 different classes
- Pyogenic (pus forming)
- Viridens
- Enterococcal
- Lactic
What Lancefield group is Streptococcus Pyogenes?
Group A beta-haemolytic streptococci (completely breaks down RBCs)
Streptococcus pyogenes has a number of virulence factors
Name as many as possible
Hyaluronic acid capsule M Protein Adhesins Streptolysins O and S Dnases A-D Hyaluronidase and Streptokinase Streptococcal pyrogenes exotins
What does a hyaluronic acid capsule do? (virulence factor of streptococcus pyogenes)
Inhibits phagocytosis
What does the M protein do? (virulence factor of streptococcus pyogenes)
Prevents phagocytosis by inhibiting activation of alternative complement pathway on bacterial cell surface
What do adhesins do? (virulence factor of streptococcus pyogenes)
Give a couple of examples
Help the bacteria adhere to epithelial surfaces (first step in colonisation/infection)
M proteins and fibronectin binding protein act as adhesins
What do Streptolysins O and S do? (virulence factor of streptococcus pyogenes)
Lysis of RBCs neutrophils and platelets (cause of haemolysis)
What do Dnases A, B, C and D do?
When neutrophils approach a bacteria to neutralise it, they condense their DNA (as they are about to self-destruct) and they expel this as a net to help catch the pathogen
Dnases break down DNA so inactivate this method in neutrophils
What do streptococcal pyrogenic exotoxins do?
They cleave IgG bound to Group A Strep (breaking down the antibody response in the host cell)
What bacteria is the common cause of streptococcal pharyngitis?
Streptococcus pyogenes (Group A beta haemolytic streptococci - which is a gram positive bacteria)
What happens if you don’t treat a patient with streptococcal pharyngitis?
The patient will develop an M protein specific antibody but there are some occasional complications such as scarlet fever
Name 4 complications from streptococcal pharyngitis
- Scarlet fever
- Suppurative complications (pus forming)
- Acute rheumatic fever
- Acute post-streptococcal glomerulonephritis
What skin infections can streptococcus pyogenes cause?
- Impetigo
- Erysipelas
- Cellulitis
- Necrotising fasciitis
What bacteria/s causes impetigo?
What can impetigo lead to?
Streptococcus pyogenes or staph aureus
It can lead to glomeuruonephritis
What are the 4 signs of toxic shock syndrome?
- Deep tissue infection with streptococcus pyogenes
- Bacteraemia (bacteria in the blood)
- Vascular collapse
- Organ failure
