PMB: Steptoccocus 15 Flashcards
1
Q
What are the characterisitics of streptococcus?
A
- Gram positive
- Catalase negative (Can’t produce catalase)
- Non-motile (doesnt move)
- Non-spore forming
- Faculative anaerobic (can grow aerobically or anarobically)
- Growth in pairs or chains
2
Q
What is classification of species/ chains dependent on?
A
- Colony morphology
- Haemolysis
- Biochemical reactions
- Serological specificity
3
Q
What categories of strepptocoi is there dependent on haemolysis?
A
Divided into groups by the type of haemolysis on blood agar
- a- Haemolysis
- B- Haemolysis
- Y- Haemolysis
4
Q
Describe the effect a-Haemolysis has on blood agar
A
- Green zone around colonies
- Complete lysis of RBC
- Incomplete degradation of Haemoglobin
5
Q
Describe the effect B-Haemolysis has on Blood agar plates
A
- Transparent zone around RBC
- Complete lysis of RBC
- Complete degradation of haemoglobin
6
Q
Describe Y-haemolysis on RBC agar plates
A
NO haemolytic activity
7
Q
Give some examples of a- and y- haemolytic streptococci
A
- •S. pneumoniae: α-haemolytic, airway infections, sepsis, meningitis
- •Oral streptococci: α- or g- haemolytic, caries caused by S. mutans and S. sobrinus
- •S. salivarius
- •S. sanguis
- •S. mutans
- •S. mitis
- •S. sobrinus
- •S. constellatus
- •S. intermedius
- •etc.
8
Q
Desribe streptococcus phenomenia
A
- Also called pneumococcus
- Cause of pneumonia, meningitis, sepsis, otitis media
- Diplococcus (pair cells)
- Surrounded by a dense capsule that makes bacteria resistant to phagocytosis
- More than 90 diffferent capulse varietnts: Serotypes
- Encapsulated strains: COlonies with smooth surfaces
- Non-encapaulsted mutants: colonies with rough surfaces
9
Q
How severe is steptoccous pneuomiea?
A
- Commonly occurs after an airway infection e.g. influenza
- It is common, but life threatening in people with weakened immune systems e.g. Eldery, infants, adults with underlying diseases
10
Q
What are the symptoms of streptococcus phenumoniea
A
- Breathing difficulties
- Chest pains
- High fever
- Reusty red sputum colour
- Can invade blood (sepsis) and meninges (meningitis)
11
Q
What is the diagnosis of S.Phenuomiea?
A
- a-haemolysis on blood agar plate
- Optochin (Antibody) sensitivity test: Zone of inhibitation around disk contain optochin
- Bile solubility test: Autolysis of bacteria upon addition of deoxycholate
12
Q
What treatment/ prevention options are available for S.Penumomenia?
A
- Treatement (After contracting infection)
- Penicillins
- Increasing resistance due to altered transpeptidases
- Macrolides:
- Used as a reserve
- Target bacterial ribosomes
- Penicillins
- Prevention:
- Polycalent polysaccharide vaccine
- ‘Recomenend in immunocompromised
- 2-3 valent vaccine for children <2 years and adults
- 7-calent conjugated vaccine for infants >2months
- Polycalent polysaccharide vaccine
13
Q
What are examples of oral streptococcus?
A
- S. Mutans and S. Sobrinus
- They attach to the teeth (enamal) and in the presence of sugarsb(Sucrose) form a biofilm which leads to plaqu formation
14
Q
How is the dental plauqe formed?
A
- Glycoproteins from saliva form a film on tooth surfaces. ORal streptococci bind to these glycproteins on the enamal and in the presence of sucrose form a biofilm. This leads to plaque formation. In the biofilm sucrose is converted to fructose and glucose.
- Fructose is fermintated to lactic acid and glucose undergoes polymerisation via glucosyl-transferase to polysaccharide occurs (mutan, glycan, dextran)
- The lactic acid in the biofilm begins to interact with the enamal which is made up of hydroxyapatite and is sensitive to low pH
- This leads to regions of the enamal dissolving and generating cavities
- These cavities colonize with streptococci and other bacteria. Bacteria relese protolytic enxymes whihc destroy the dentin
15
Q
What is serological classification of B-haemolytic streptococci/
A
Can be grouped based on 2 different methods:
- Different carbohydrates present on bacterialc cell walls
- Lancefield serogrouips (A-V)
- Subtyping based on proteins in cell wall
- S.Pyrogenes Mtype 1-83
16
Q
What detectio method can be used for B-haemolytic streptococci?
A
- Latex Agglutination tesr
- POstive response - clumping
- Negative response - no clumping
17
Q
- What group does Streptococcus pyrogens belong too?
- What does it cause
- What is the treatment?
A
- Only species in group A of lancefield serogroup A
- Causes:
- Skin infections e.g. Necrotizinf fasciitis
- Sore throat
- Toxigenic infections
- Immunological diseases
18
Q
What is the treatment for streptococcus Pyrogenes?
A
B-lactams ABs
19
Q
Describe skin infections caused by streptococcus pyrogenes
A
- Necrotizing Fascitis
- Agressive skin infection
- Multiple pathogenic factors involved e.g. proteases, toxins, super antigens.
- Bacterial toxins interfere with blood flow to tissues - this can lead to infection in these tissues
- Digestion of tissue proteins by proteases - allows spread of bacteria
- Can cause systemic effects like septic shock
20
Q
What are other disease caused by S.Pyrogenes?
A
- Pyrogenic infections of throat: tonsilitis
- Toxinogenic fevers: scarlet fever
- Immunological diseases: Rheumatic fever a post-streptococcal disease
21
Q
What is tonsilitis
A
- Severe sore throat
- sore or difficulty swallowing
- headache
- fever and chills
- changes or loss in ones voice
22
Q
What are your tonsils and what happens to them during tonisilits?
A
- pair of speicalised lymph nodes behind the tounge
- Store white blood cells to engulf bacteria and viruses which enter the nose or mouth
- When overwhelmed by bacteria, they becoe swollen and inflammed
23
Q
What is scarlet fever cause by and what are the symptoms?
A
- Cause: Rare form of S.Pyrogenes infection. Caused by a lysogenized strain of S.Pyrogenes: a phage codes for an erythrogenic toxin
- Symptoms:
- Red rash on body that feels like sand paper
- Strawberry tougne: Red tounge with prominant piapillae
- Sore throat
- fatigue
24
Q
What are the complicaitons of scarlet fever for children?
A
- Serious complicatinose.g. rheumatic fever and acute glomerulonephritis
25
Q
What is rheuam
A
- Occurs after a streptococcus pyrogene infection e.g. strept throat or scarlrt fever
- It is an immune response which causes inflammation and damge to certain organs, particularly the heart.
- The ABs prodcues by the body against the intital streptococcus (M protein) infection cross-react with the heart and attack the bodies own cells
26
Q
Rheumatic fever symptoms
A
- Fever
- Wekaness
- Abdominal pain
27
Q
What is glomerulonephritis?
Symptoms
A
- •Acute glomerulonephritis:
- •blockage of glomeruli by streptococcal immuno-complexes
- •Symptoms of the disease:
- •blood in the urine
- •high blood pressure
- •decreased or increased urine output
28
Q
What makes combating S.Pyrogenes difficult?
A
- M protein receptors on bacterial cell wall bind to fibrinogen and prevent acess for ABs to bind
- S.Pyrogenes produces peptidase C5a peptidase which cleaves immune component C5a. This prevents the migration and movement of macrophages which would normally attack S.pyrogenes
- The capsule surface of S.Pyrogenes contains Hyaluronic acid. This is specific to eukaroytes and can mean immune cells don’t recoginize the bacteria as forgin and produce ABs
- May over stimulate T cells and AB by B lymphocytes. This can lead to toxic shock and organ failure (more info next slide)
29
Q
Superanitgen notes
A
- Uptake of antigen by antigen presenting cell; processing and presentation in major histocompatibility complex (MHC II)
- Recognition of antigen by T helper cell with suitable receptor (0.01%)
- Cytokine production; antibody production by B lymphocytes
- Superantigen links MHC II receptor to any T helper cell
- overstimulation of T helper cells; overproduction of cytokines
- may result in toxic shock: organ failure
30
Q
Describe adhesion an dinvasion
A
- Adhesion mediated by protein F
- isolated protein in the bacterial cell wall binding to fibronection on host cell surface
- Invasion of the body mediated by
- Streptolysin, a hemolysin
- Streptokinase and Hyaluronidase,
spreading factors
