Bacterial pathogenesis and infectious disease Flashcards
Gram staining
Form of staining that identifies if bacteria has peptidoglycan in their cell wall.
Positive= Purple= has it Negative= pink= does not have
Some bacteria do not stain well
- Mycobateria
- Mycoplasma
- Chlamydia
Bacterial shapes
Cocci
- Spherical
- Examples: staphylococcus, streptococcus
Rods/ Bacilli
- Examples: E.coli, Neisseria
Spirals
Vibrio
Aerobe bacteria
Use O2 as a final electron acceptor (aerobic respiration)
Example:
- S.aureus
Anaerobe (obligate) bacteria
In respiration, organic molecule is final electron acceptor.
Example
- Clostridium
Facultative anaerobic bacteria
Bacteria that has the ability to switch between aerobic and anaerobic metabolism
Example
- E coli.
Haemolytic streptococci classification
Alpha haemolytic (veridans_
- Cause partial haemolysis of blood agar
- Greenish colour
Beta- haemolytic
- Causes complete haemolysis
- Translucent agar
Gamma-Haemolytic
- No haemolysis
- Blood agar stays brown
Factors that affect the pathogenicity of a bacteria
The immune status of the patient
The site of the infection.
The virulence of the bacteria.
Examples of gram positive cocci
S. Aureus
Coagulase negative Staphylococcus
Streptococci
- Group A (S.pyogenes), B, C, G
- D= enterococcus
- S. pneumoniae
- Viridians
Peptococus/ Peptostreptococcus
Exams of gram positive rods
B. cerus
B.anthracis
Corynebacterium
Listeria monocytogenes
Clostridium
Gram negative cocci
Neisseria
- N. meningitidis
- N gonorrhoea
Moraxella catarrhalis
Gram negative rods
Haemophilius influenzae
Enterobacteriaciae
- Salmonella and Shigella
- E.Coli
- Klebsiella
- Enterobacter
- Proteus
Pseudomonas
Bacteroides
Campylobacter
Helicobacter
Vibrio cholerae
Bordetella pertussis
Legionella
Secretory proteins from S.aureus
Superantigens
- TSST-1
- SEA
- SEB
Exfoliative toxins
- Proteases
- Target epidermal proteins
Cytolysins
- Alpha-toxins
- PVL
Surface proteins from S.aureus that increase its virulence
Coagulase
-Stimulates clotting allowing immune invasion
Protein A
- Binds to Fc portion of IgG
- immune cloaking
Adhesins: Allow tissue adherence and colonisation. Mechanism in deep infections, allows immune cloaking
- Elastin binding protein
- Collagen binding protein
- Fibronectin binding protein
Staphylcoccal toxins
Cytotoxins
- Pore forming toxins
Example
- Panton-valentine leukocidin (PVL) lyses polymorphs (associated with MRSA in USA)
Enterotoxins
Superantigens
- Targets the gut
- Causes
diarrhoea
Scalded skin syndrome
Also known as Ritter’s disease
Exfoliative toxin A,B
- Serine protease for desmoglein 1
Toxic shock syndrome
Caused by release of super antigen TSST
Signs and symptoms
- Characteristic rash
- High fever
- Hypotension–> septic shock
- Multiorgan failure
S.aureus food poisoning
Cause by enterotoxins
Ingestion causes violent vomiting
S. aureus bacteremia
Causes
- Endocarditis
- Osteromyelitis
- Septic arthritis
Coagulase negative staphylococcus
Less virus Staph
Commonly infects central venous line infections
- Endocarditis
- Orthopaedic surgical
- Graft, implants
Example
- S.epidermis
Examples of alpha haemolyin strep
S. milleri
S. mites
S. sangria
S.pneumoniae
E.coli virulence
Adhesins
Siderophores
Capsule
Toxins
- Endotoxin
- Exotoxins (entero, vero)
E coli adhesins
P fimbria
- Binds to RBC p antigen
- Also binds to uroepithelial antigen
- Associated with pyelonephritis
Non fimbral GI adhesins
- EPEC (enteropathogenic)
- EIEC (enteroinvasive)
Siderophores
Enterobactin
- Iron chelator
Allows servival in environments with low Fe3+
E coli capsule
Protect E coli from complement mediated response
K1 capsular serotype associated with neonatal meningitis
E coli toxins
Endotoxins
Cytolysin
Enterotoxins
- Causes fluid leak in GI tract (diarrhoea)
Verotoxins
- Disrupts ribosomal protein synthesis= haemorrhage diarrhoea (Enterohaemorrhagic E coli)
- Associated with haemolytic uraemia syndrome
E coli disease
Commonest cause of UTI/ urosepsis
GI and biliary sepsis
Nosocomial (Hospital acquired) infection
- Wounds
- Devices
- Pneumonia
Lancefield groups
Classification of Strep via surface antigens
- Carbohydrate antigens
Groups A,B, C etc
Examples of beta-haemolytic strep
Lancefield groups A-C, G.
S. pyogenes (Group A)
S. dysgalactidae (Group G)
S. equi (Group C)
S. agalactidae (Group B)
S pyogenes exotoxins[4]
Superantigen (SpeA, SpeC)
- Causes toxic shock like syndrome.
Causes rash and fever through overstimulation of T cell response.
Hyaluronidase
- Breaks down hyaluronic acid, which facilitates spread by destroying cohesiveness of connective tissue.
Streptokinase
- Activates plasminogen into plasmin which breaks down fibrin and prevents blood clotting
Streptolysin
- Causes complete lysis of red blood cells.
M protein
Endotoxin on S. pyogenes
- alpha helical coiled coil structure
Binds to serum factor H, preventing opsonization
C5a peptidase
Endotoxin on S pyogenes
- Inhibits cleaving of C5a= less chemotaxis of neutrophils
Molecular mimicry of strep infections
M protein is homologous with cardiac myosin/ trophomyosin and glomerular basement membrane proteins.
Strep infection can lead to cross-reactive anti-self responses
Leads to post-strep
- Rheumatic fever
- Glomerulonephritis
- Guillain Barre
- HLA B27 spondyloarthropathies.
