Bacterial Virulence Flashcards
What is the importance of virulence factors?
They contribute to microbes ability to cause pathology
What do adhesins do?
Enable binding of the organism to the host tissue
What does invasion do?
Allows the organism to invade a host cell/tissue
What is the function of impedin?
Lets the organism avoid host defence mechanisms
What does aggressin do?
Causes damage to the cell directly
What is the function of modulin?
Induces damage to the cell indirectly
What are virulence factors?
The factors responsible for variation in virulence within and between species
What does SSTI stand for?
Skin and Soft Tissue Infection
What microbiology causes SSTIs?
Natural flora, gram +/-, Staphylococcus, Streptococcus, Propionibacterium, Corynebacteria, Yeast
What are the two common species of staphylococci involved in skin infections?
S.epidermidis and S.aureus
Where is S. epidermidis found?
Skin and mucous membranes, 100% colonisation (nosocomial infection/immunocompromised)
What is S.epidermidis associated with?
Foreign devices
What is the percentage colonisation of S.aureus?
20-60%
Where is S.aureus found?
Anterior nares and perineum (nasal strain can protect), nosocomial and community
How is MRSA defined?
By resistance to flucloxacillin (mainly nosocomial)
Who gets MRSA?
Elderly and immunocompromised, ICU and burns patients, patients with IV lines and on dialysis
How does S.aureus infection present?
Superficial lesions (boil-abscesses), systemic manifestations (life threatening), toxinoses (toxic shock)
What are some examples of toxinoses?
TSST-1, Staphylococcal food poisoning, Scalded skin syndrome
What are toxinoses?
Illnesses caused by bacterial toxins alone
What are some features of TSST-1?
Rapid progression (48hrs), high fever, vomiting, diarrhoea, sore throat, muscle pain
What are some features of Staphylococcal food poisoning?
Intoxication, 1-5 hrs, vomiting, diarrhoea
What causes Staphylococcal food poisoning?
Enterotoxin SeA, SeB and SeC
What causes Scalded skin syndrome?
Exfoliatin toxins, ETA and ETB toxins target desmoglein-1 (DG-1)
Who gets scalded skin syndrome and where does if occur?
Often neonatal; occurs in face, axilla and groin
How do superantigens work?
Activate 1 in 5 T cells, antigen is processed by PMN and binds directly to MHC II complex, causes massive release of cytokines and inappropriate immune response
What is TSST-1 associated with in particular?
Toxic shock syndrome
What are the diagnostic criteria for toxic shock syndrome?
Fever=39C
Diffuse macular erythroderma and desquamation
Hypotension = 90 mmHg (adults)
>/= 3 organ systems involved (liver, blood, renal etc)
What are adhesins involved in?
Attachment/colonisation
Where are extra cellular matrix molecules present?
Epithelial and endothelial surfaces as well as a component of blood clots
What are some methods that viruses use to evade host defences?
Protein A, Proteases, Superantigens, Lipases, Phospholipases, Esterase, Coagulase
What does PVL stand for?
Panton-Valentine Leukocidin
What are the two bicomponent toxins present in PVL?
lukS and lukF
What does PVL have a specific toxicity for?
Leukocytes
Name some conditions associated with PVL?
Recurrent furunculosis, sepsis/ necrotising fasciitis
What have PVL and the a-toxin linked with CA-MRSA been associated with?
Necrotising pneumonia and contagious severe skin infections
What precedes necrotising pneumonia?
Influenza-like syndrome
Is necrotising pneumonia haemorrhagic?
Yes
How does necrotising pneumonia progress?
Acute respiratory distress, deterioration in pulmonary function, refractory hypoxaemia, multi-organ failure despite antibiotic therapy
What are some ways virulence factors impact on clinical care?
Next generation sequencing, molecular techniques (PCR, antibodies), diagnosis (understanding pathology/risk), epidemiology, vaccines/anti-infectives, novel approaches (e.g replacement therapy)
What are some features of Streptococcus pyogenes?
Gram + cocci, chains, catalase negative, GAS (beta haemolysis)
How is Streptococcus pyogenes classified?
Using the Lancefield system (surface antigen), serotyping of cell wall carbohydrate, C polysaccharides extracted from cell wall
What are the major serotypes of Streptococcus pyogenes?
A-H and K-V (20 types), group A further divided according to M proteins (M1 and M3 are major serotypes, M3 and M18 cause severe invasive diseases)
What are the two kinds of viral capsule?
Mucoid and microcapsule
What are some conditions linked to Streptococcus pyogenes?
Impetigo, Cellulitis, Necrotising fasciitis, Toxic shock like syndrome (TSLS)
Where does the infection of Impetigo take place?
Usually the face, infection is immediately below surface
Is Impetigo contagious?
Yes-highly contagious through contact with discharge on the face
What is cellulitis?
General term for a deeper infection in the dermis that isn’t associated with necrosis, range of spreading subcutaneous skin infections
What is the primary infection/trauma of cellulitis associated with?
Associated with the organism spreading through the blood and seeding cellulitis
What is Erysipelas?
Localised cellulitis-fever, rigors, nausea
What causes necrotising fasciitis?
Invasive Strep.A strains penetrate mucous membrane and develop in lesion, rapidly destroys connective tissue, may have TSLS
What bacteria causes Type 1 necrotising fasciitis?
Clostridia spp.
What does iGAS stand for?
Invasive Group A Strep.
What causes TSLS?
Pyrogenic exotoxins
What are some features of TSLS?
Complication of invasive infections, 30% mortality, hours-days, hypotension to organ failure, SpeA/B/C/F
How do haemolysins cause cell destruction?
Second soluble oxygen labile haemolysin SLO contributes to tissue destruction
What is Streptolysin S (SLS)?
Pore forming cytolysin, toxic to PMN and organelles as well as platelets, causes tissue and cell destruction
What are some of Strep. pyogenes virulence factors?
Superantigenic toxins, capsule, Haemolysins SLO/SLS cause tissue damage and ulcers
What does the M protein in the Strep. pyogenes capsule bind to?
Factor M, fibronectin, fibrinogen, albumin
What are the features of toxic shock caused by S.aureus?
Localised infection, no bacteremia, menstrual TSST-1, non-menstrual SEB/SEC, pyrogenic toxin
What are the features of toxic shock caused by Strep. pyogenes?
Invasive disease (pharyngitis), SpeA/SpeC most common toxin, pyrogenic toxin
What is the virulence factor involved in toxic shock caused by both S.aureus and Strep. pyogenes?
Superantigens
What are the toxic shock toxins of S.aureus?
TSST-1, SEA, SEB
What are the toxic shock toxins of Strep.pyogenes?
SpeA, SpeC
How does virulence vary?
Strain evolution through mobile genetic elements encoding virulence determinants?
What are some mobile genetic elements that encode for virulence determinants?
Plasmids, bacteriophage, transposons and IS, pathogenicity islands (PI)
What do opportunistic infections and toxinoses depend on?
Genotype and expression of virulence proteins
Where is Strep. pyogenes normally found?
In the pharynx (also adheres to skin)
How can toxic shock be produced by more than one organism?
Due to production of similar exo-proteins, common virulence factors and disease mechanisms
Is S.aureus coagulase positive or negative?
Coagulase positive
Is S.epidermidis coagulase positive or negative?
Coagulase negative
What are some examples of adhesins?
Fibrinogen-binding (ClfA/B), Fibronectin-binding (FnbpA/B), Collagen binding (CNA), Elastin binding protein (Ebps)
