bacterial pathogenesis and infectious disease Flashcards
what are the different shapes of bacteria?
- cocci- round
- bacilli- rods
- spirals
- vibrio
what do gram positive bacteria stain?
purple
what do gram negative bacteria stain?
pink
what is the cell wall of gram positive bacteria like?
- thick peptidoglycan layer
- lipoteichoic and teichoic acid layer
what is the cell wall of gram negative bacteria like?
- thin peptidoglycan layer
- outer and inner membrane
- lipopolysacharides (lps)
- proteins ad pores
What is an example of an obligate aerobe?
clostridium
what is an example of an anaerobe?
s.aureus
what are the different types of haemolytic streptococci?
- α haemolytic ‘viridans’ streptococci
These cause partial haemolysis of blood agar and a greenish colour - β haemolytic streptococci
These cause complete haemolysis making the blood agar translucent - γ (non)- haemolytic streptococci
what are the different things that confer virulence of the s.aureus infection?
Coagulase
Stimulates clotting
Role in immune evasion
Not expressed by less virulent ‘coagulase negative’ staphs
Adhesins: bind host proteins
- elastin binding protein, collagen protein, fibronectin binding protein
cytotoxins- including cytotoxins, exfoliative toxins and super antigens
what is an example of a facultative anaerobe?
e.coli
what are the 4 different ways of describing bacteria?
- staining
- growth- aerobes vs anaerobes
- morphology
- microscopic
- macroscopic- on agar - typing
- related species
primary serology
- correlating genotypes
what is a commensal bacteria?
- bacteria which is probably not causing disease when taken from a clinical sample
what is a pathogen?
- a bacteria that is probably causing disease when identified from a clinical sample
what are the 3 things that make bacteria pathogenic rather than commensal?
- The immune status of the patient.
- The site / sample in question.
- The disease causing properties of the bacteria (virulence).
what type of bacteria are streptococcus pyogenes and streptococcus aureus?
gram positive cocci
what type of bacteria is e.coli?
gram negative rods
when are surface proteins most responsible for virulence in s.aureus?
the exponential phase
when are secreted proteins most responsible for virulence in s.aureus?
the stationary phase
- secreted proteins include toxins
what does protein A do in s.aureus?
- binds the FC portion of IGg
- involved in immune cloaking
what are the actions of adhesin in s.aures?
- tussle addrehence
- for colonisation
- allows deeper infections
- allows immune evasion by cloaking
what are the 4 main types of staphylococcal toxin and what are they involved in?
- cytotoxin
- PVL lyses polymorphs and has a role in MRSA - exfoliative toxins
- proteases
- target epidermal structural proteins - exotoxins
- superantigens
- cause massive Tcell response in toxic shock syndrome - enterotoxin
- ingestion leads to vomiting and diarrhoea
what is ritter’s syndrome?
- caused by exfoliative toxin
- serine proteases specific fro desmoglein 1
- causes sheet-like desquamation
what are the different ways that s. aureus infections can manifest?
- normal comensal
- soft tissue infection
- vascular line related infection
- bacteremia
- surgical site infections
- toxin mediated infections
what are some s.aureus bacteraemia?
- endocarditis
- osteomyelitis
- septic arthritis
what type of bacteria is s.epidermsis?
- coagulase negative gram poitive staph
- found normally on skin surface
what things can s.epidermis cause when it becomes pathogenic?
- Central venous line infection
- Endocarditis (prosthetic valve)
- Orthopaedic surgical infections
- Foreign material in a ‘sterile’ place
grafts, implants etc
where do streptococci colonise?
a huge family of Gram positive bacteria which colonise the GI tract and skin
what are the 3 ways to classify streptococci?
- Appearance on blood agar (haemolysis)
e. g ‘beta haemolytic strep’ - Lancefield groups (A, B, C etc)
Surface carbohydrate antigens
e.g. ‘group A strep’ - True species names (S. pyogenes, S. pneumoniae etc) e.g.
how is s.pyogenis classified?
S. pyogenes = group A strep and is a beta haemolytic strep
what are superficial infections caused by strep. pyogenes?
Pharyngitis
Cellulitis
what are deep infections caused by s.pyoges?
- myositis
- necrotising faciatis
what are 2 common autoimmune sequelae of s.pyogenes?
Rheumatic fever – a major cause of heart disease
glomerulonephritis
what are the virulence factors in s.pyogenes?
M PROTEIN
- Fibronectin binding protein
- collagen binding protein
- c5a peptidase
how is streptococcal M protein involved in pathogenesis of S.pyogenes?
- Binds serum factor H – regulator of complement activation
- Prevents opsonisation
2.Has an alpha-helical ‘coiled-coil’ protein
Molecular mimickry
how can molecular mimicry lead to post strep heart disease?
- M protein is a a helical coiled coil structure
- has homology to cardiac myosin and tropomyosin
- recurrent childhood infection can cause cross reactive anti self response which damages the heart
occurs after rheumatic fever
how can molecular mimicry lead to post strep glomerular nephritis?
- M protein has alpha helical coiled coil structure
- which has homology with glomerular basement membrane
- after recurrent childhood infection a cross reactive anti self response can occur
what type of bacteria are enterococcus?
gram positive coccus
what are examples of gram negative rods?
Klebsiella
Enterobacter
Citrobacter
what can occur when opportunistic infections gain access to sterile sites?
- wound infections
- HAP
what are 3 main diseases caused by E.coli?
UTI
Enteric
Meningitis (Neonatal, elderly, immunocompromised)
what are 4 main virulence mechanisms of e.coli?
- adhesins
- p. fimbria= pyelonephritis associated
- non fimrial= GI Adhesin causing diarrhoea - sidephores
- enterobactin
- powerful iron chelators
- essential for survival in tissues - capsule
- protects against complement
- K1 serotype allows crossing the BBB to cause meningitis in neonates - toxins
- enterotoxin- cause GI leak
- verotoxin- disrupt ribosomal protein synthesis
which pathogen is the biggest cause of urosepsis?
e. coli
