26 Staphylocci and Streptococci Flashcards
how many are in the staphylococci genus
approx 50 different species
what is the most common/important species causing human disease -staph
Staphylococcus aureus
what is the second most important species in humans - staph
Staphylococcus epidermidis
what gram is staph
positive
what morphology is staph
cocci form in clusters of cells
examples of staphylococcus aureus infections/syndromes include
- impetigo
- sepsis
- food poisoning
- TSS
- septic arthritis
what are the infections of staph like
Many of these infections are relatively minor and superficial – skin and soft tissue infections
what are some staph infections like
associated with entry into the bloodstream to cause more serious disease in deeper tissues
Some S.aureus diseases are associated with production of specific toxins
where is staph aureus present
Around 50% of population carry it
- permanently
- intermittently in back of nose
Also carried in armpits (axillae), groin and gut
what type of bacteria is staph
usually commensal
when is staph harmful
S. aureus penetrates skin and find way into other body sites can cause disease = opportunistic pathogen
what are endogenous infections
infect self, own S. aureus by transfer from nose, axillae or groin to site of tissue damage e.g. cut, surgery
what are exogenous infections
S. aureus transferred from another infected individual, carrier or from environment to site of tissue damage
how can staph aureus survive in environment
S. aureus resists desiccation = can survive in environment in dust and surfaces
what immune responses are triggered due to S. aureus
Innate and acquired immune responses
phagocytosis
when is phagocytosis triggered in staph infection
Phagocytosis after opsonisation by AB and complement important for controlling infection
what is used to prevent staph aureus infection
no vaccine available
how good is the immune system at removing staph infection
not always able to eliminate infection or prevent re-infection with staphylococci
what are the staph virulence factors associated with
production of a large number of surface proteins, toxins and immune evasion factors
what are the virulence factors - surface proteins
Surface proteins act as adhesins for colonisation, receptors for nutrient uptake and protect against immune responses
how can staph aureus isolates exchange genes
by horizontal gene transfer e.g. on plasmids, transposons, bacteriophage…
Virulence factors promoting invasion and tissue damage include
- enterotoxins
- proteases
- lipases
Virulence factors promoting colonisation include
- clumping factors
- protein A
- adhesins
what is staph aureus adhesins important for
Adhesion important in initial infection stage – colonisation
what does the staph aureus adhere to
mammalian cells e.g. nasal epithelial cells, also biomaterial surfaces e.g. catheters
example of a staph aureus adhesin family
MSCRAMMs
what is MSCRAMMs
Microbial Surface Components Recognising Adhesive Matrix Molecules
what do MSCRAMMs do
Bind to mammalian extracellular matrix (ECM) proteins e.g. fibronectin, fibrinogen collagen etc.
what are MSCRAMMs involved in
Involved in initial tissue colonisation e.g:
- FnbA/B - Fibronectin binding proteins
- Cna - Collagen binding protein
examples of staph aureus toxins
Panton Valentine leucocidin Alpha-hemolysin Phenol soluble modulins Exfoliative toxins A and B Toxic shock syndrome toxin Enterotoxins
what does PVL do
lyses neutrophils
what does alpha-hemolysin do
lyses RBC, inhibits neutrophil chemotaxis
what do phenol soluble modulins do
cytotoxic peptides which are active against leukocytes – induce chemotaxis, induce IL-8 production and cause neutrophil lysis (intracellular)
what do ETA/B do
cause symptoms of scalded skin syndrome by splitting the dermis from the epidermis in skin
what does TSST-1 do
TSS by acting as a superantigen to non-specifically trigger excessive cytokine production by T cells
what do enterotoxins do
cause food poisoning (intoxication) can also act as superantigens causing TSS
Examples of S.aureus virulence factors that affect immune function
Antibody function
Complement activation or function
Antibody and Complement functions
what is the AB function in S.aureus virulence factors that affect immune function
Protein A and Staphylococcal binder of immunoglobulin (Sbi) are proteins that interfere with opsonisation by AB
what is the complement activation in S.aureus virulence factors that affect immune function
staphylococcal complement inhibitor (SCIN) interact with bacterial bound C3 convertases which facilitate C3b binding to bacterial surface – normally promotes opsonisation and phagocytosis
what is the AB and complement functions in S.aureus virulence factors that affect immune function
Staphylokinase activates plasminogen to make active protease – plasmin, can degrade complement opsonin C3b and Fc component of immunoglobulins
where is staphylococcus epidermis found
Member of normal skin flora
what are the Staphylococcus epidermis infection causes
tend to be less acute than those caused by S. aureus – infection is subacute or chronic
what is most important about staph epidermis in infections
Most important as cause of biomaterial related infection
- infections associated with medical device use
what makes biofilms
S.epidermidis and S.aureus can both form biofilms on biomaterials such as catheters
how does a biofilm form
Bacteria are encased in a matrix consisting of bacterial polysaccharides and extracellular DNA released from dead bacterial cells
what is a biofilm
Bacteria grow attached to the catheter surface to form a three dimensional aggregate
how are biofilms treated
Bacteria growing in biofilms may be more difficult to treat with antibiotics
are biofilms easy to killl
Bacteria in biofilms are more difficult for phagocytic cells to ingest and kill
how many species does the streptococci genus contain
around 40 species
what are most streptococci like
many Streptococci are commensal bacteria – but may act as opportunistic pathogens
what are some streptococci
Some Streptococci are primary pathogens – able to cause disease in fit, healthy people
what gram are streptococci
Gram positive
what is the morphology of streptococci
cocci which form chains or pairs of cells
Streptococci – main pathogens
Streptococcus pyogenes Streptococcus pneumoniae
Streptococcus mutans, Streptococcus mitior etc
what does Streptococcus pyogenes cause
things including: Sore throat, scarlet fever, skin infection, bacteraemia, toxic shock
what does Streptococcus pneumoniae cause
things including: Pneumonia, sinusitis, meningitis
- A vaccine is available to prevent S.pneumoniae infection
what does Streptococcus mutans, Streptococcus mitior etc cause
things including: Dental caries, Infective endocarditis
what does Streptococcus pyogenes infect
only humans
what is the source of strap pyogenes infection
other infected individuals
what Lancefield Group is strep pyogenes
Group A (Group A Strep – GAS)
what is lancefield grouping
Lancefield typing system differentiates streptococci based on differences in their surface polysaccharide antigens
what is characteristic of strep pyogenes
b- haemolytic makes haemolysin – Streptolysin S – which breaks down red blood cells
what is used to prevent strep pyogenes infections
Currently no vaccines are available to prevent S.pyogenes disease
what are some of the non-invasive diseases that strep pyogenes causes
Pharyngitis
Scarlet Fever
Skin infections
where do non-invasive diseases infect
Upper respiratory tract commonest site of infection and entry to the body
who carries strep pyogenes
People recovering from infection may carry S.pyogenes in the throat
Few healthy adults carry S.pyogenes but in young school children >10% may carry the organism
what does pharyngitis cause
- Sore throat, fever, malaise and headache
- Enlarged tonsils
what is pharyngitis known as
“Strep sore throat”
what does scarlet fever cause
- Causes a diffuse rash on the skin and mucous membranes
- Eventually the tongue goes red - “Strawberry tongue”
what causes scarlet fever
Follows throat infection by some strains of S.pyogenes that produce erythrogenic toxins
examples of skin infections
- Impetigo
- Erysipelas
what is erysipelas
more serious –affects superficial skin layers – may lead to cellulitis and spread to bloodstream to cause bacteraemia
what is sequalae of S.pyogenes infections
In some people, additional symptoms develop 1-5 weeks after the initial infection
“sequalae” are thought to be due to immune reactions to S.pyogenes which induce an autoimmune response against host tissues
what is an example of sequale - strep pyogenes
e.g Rheumatic fever after Strep sore throat
what is acute post-Strep glomerulonephritis
Immune complex mediated disease affecting the kidneys
what is an Invasive S.pyogenes disease
Infection spreads into deeper soft tissues
what are invasive S.pyogenes diseases associated with
These infections are frequently associated with bacteraemia
who is at risk to invasive diseases
Invasive disease may occur in healthy people but people with chronic illnesses are at increased risk
e.g patients with cancer, diabetes, dialysis patients, patients on steroids
examples of invasive diseases - strep pyogenes
Necrotising fasciitis
Strep TSS
bacteraemia
what does Necrotising fasciitis cause
- Infection destroys fat and muscle fascia – skin may not be affected
- Infection is progressive, and bacteraemia leads to systemic shock
what causes Strep TSS
by release of streptococcal toxins into the bloodstream
what causes bacteraemia
S.pyogenes grows very rapidly in the bloodstream
what can bacteraemia cause
acute endocarditis
what is the mortality rate for bacteraemia
40%
what allows S.pyogenes to cause infection - disease
Disease causation involves adhesion, avoidance of components of the immune system and toxin production
why is s. pyogenes able to cause range of diseases
S.pyogenes produces a range of virulence factors which contribute to these functions
how can genes encoding virulence factors for S. pyogenes by transferred
Genes encoding virulence factors may be transferred horizontally by bacteriophage
where does S.pyogenes binds to
connective tissue protein fibronectin in the pharynx and on the skin
where do the adhesins anchor - s. pyogenes
anchors the bacterium into that location so it is able to persist
what mediates s. pyogenes adhesins
Adhesion is mediated by the F protein which also mediates internalisation of S.pyogenes into cells
what is involved in adhesion
M protein
lipoteichoic acid
what do M proteins form
fibrillar structures on the bacterial surface
how many M proteins are there
over 80
why is recurrence of strep pyogenes common
Antibody against one M protein won’t affect function of a different type
what is the effect of M protein presence
prevent phagocytosis
what do M proteins bind to
host proteins such as fibrinogen, plasminogen and IgG and IgA to their surfaces which can mask the bacterium from immune system
what is factor H
causes destabilisation of major complement opsonin C3b = bacterium may not be recognised by phagocytic cells so is able to persist in the tissues
what does s. pyogenes make
makes C5a peptidase
what does C5a peptidase do
degrades C5a, a product of the complement system
what do some s. pyogenes strains contain
capsule – made of hyaluronic acid
what is the effect of hyaluronic acid capsule of s. pyogenes
Capsule is anti-phagocytic because it is made of the same hyaluronic acid polymer which forms part of the connective tissue in humans
= immune system does not recognise the capsule as “foreign” no immune response is induced
what are the s. pyogenes toxins
Streptolysins
Pyrogenic exotoxins
what are the streptolysin toxins
Streptolysin O
Streptolysin S
what is streptolysin O
secreted exotoxin
what does streptolysin O cause
acute effects on heart muscle – lethal in animals
what is streptolysin s
surface bound
what does streptolysin S cause
beta-haemolysis
what are the pyrogenic exotoxins
SPEA, SPEB, SPEC and others
what is the effect of pyrogenic exotoxins
lethal in animals
what do the pyrogenic toxins cause
rash seen in scarlet fever
what are pyrogenic toxins known as
superantigens
what does a superantigen cause
antigen-independent activation of T cells
what is the result of superantigen
- over production of pro-inflammatory cytokines such as IL-1 and TNF – a
- inflammation, tissue damage, shock and organ failure – may be lethal
what does hyaluronidase do
S.pyogenes virulence factors
enzyme degrades hyaluronic acid in connective tissue
what is streptokinase
S.pyogenes virulence factors
enzyme activates a host protease precursor (plasminogen) to produce an active protease called plasmin
what does the plasmin do made from streptokinase
degrades fibrin clots which may form around the site of tissue damage and infection
what does the streptokinase allow
S.pyogenes to escape and spread into surrounding tissue
what is streptokinase used to treat
used therapeutically in patients who have had heart attacks to break down fibrin clots
what is Streptococcus pneumoniae
member of the normal oropharyngeal flora of between 5 and 70% of the human population
what can Streptococcus pneumoniae cause
e.g influenza, bronchitis, diabetes
what is streptococcus pneumoniae
a - haemolytic Streptococcus
what does streptococcus pneumoniae make
produces hydrogen peroxide which reacts with haemoglobin to produce methaemoglobin resulting in a characteristic greening around bacterial growth on blood agar
what is S.pneumoniae meningitis
Among the leading causes of bacterial meningitis
where does the S.pneumoniae move in infection
Bacterium moves from the pharynx into the bloodstream and crosses blood-brain barrier to reach meninges
what can s. pneumoniae cause
sepsis
what does s. pneumoniae make
polysaccharide capsule which is a major virulence determinant
what is the effect of S.pneumoniae virulence factors - anti-phagocytic
inhibits complement deposition and phagocytosis in the absence of type specific antibody
what is the effect of S.pneumoniae producing a capsule
produce particular capsule type will induce antibody production against the capsule, but this antibody will not protect against re-infection with S.pneumoniae carrying a different capsule type
what vaccine is there for s. pneumoniae
vaccine based on the polysaccharide capsule antigens from 23 different serotypes has been used for a number of years
what does IgA1 protease do
Cleaves IgA1 – the main antibody type found in the upper respiratory tract mucosa
Prevents the antibody from binding to the bacterium
what is Pneumolysin
intracellular, membrane damaging toxin which is released from S.pneumoniae when it undergoes autolysis
what does pneumolysin cause
Inhibits neutrophil chemotaxis, phagocytosis and the respiratory burst involved in killing of phagocytosed bacteria
what is autolysin
enzyme produced by S.pneumoniae which breaks down the bacterial peptidoglycan in the cell wall
what does autolysin release
pneumolysin and fragments of peptidoglycan from the bacterial cells
